ladybird/Libraries/LibJS/Rust/src/bytecode_cache.rs

/*
 * Copyright (c) 2026-present, the Ladybird developers.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

//! Versioned serialization for fully compiled JavaScript bytecode cache blobs.
//!
//! The format is expressed as small record types with `Encode`
//! implementations. The matching decoder should mirror these records instead
//! of growing a separate procedural parser.

use std::collections::HashMap;
use std::ffi::c_void;
use std::ops::Range;
use std::rc::Rc;

use crate::bytecode::basic_block::SourceMapEntry;
use crate::bytecode::ffi::{
    AbstractOperationKind, ConstantTag, FFISharedFunctionData, FFIUtf16Slice, WellKnownSymbolKind,
};
use crate::bytecode::generator::{
    AssembledBytecode, ConstantValue, ExceptionHandler, FunctionSfdMetadata, Generator, LocalVariable,
    PendingClassBlueprint, PendingClassElement, PendingLiteralValueKind, PendingSharedFunctionData,
    PrecompiledFunction,
};
use crate::bytecode::operand::PropertyKeyTableIndex;
use crate::bytecode::validator::{
    FFIExceptionHandlerOffsets, FFIValidatorBounds, ValidationErrorKind, validate_bytecode,
};
use crate::{CompiledProgram, CompiledProgramBytecode, ModuleCallbacks, ast, u32_from_usize};

const MAGIC: &[u8; 8] = b"LBJSBC\0\0";
const FORMAT_VERSION: u32 = 10;
const SOURCE_HASH_SIZE: usize = 32;
const BYTECODE_ALIGNMENT: usize = 8;
const COMPLETION_TYPE_VARIANT_COUNT: u32 = 6;
const ITERATOR_HINT_VARIANT_COUNT: u32 = 2;
const ENVIRONMENT_MODE_VARIANT_COUNT: u32 = 2;
const PUT_KIND_VARIANT_COUNT: u32 = 5;
const ARGUMENTS_KIND_VARIANT_COUNT: u32 = 2;

fn source_span_is_valid(start: u32, end: u32, source_len: usize) -> bool {
    let start = start as usize;
    let end = end as usize;
    start <= end && end <= source_len
}

fn source_range_is_valid(offset: usize, length: usize, source_len: usize) -> bool {
    offset <= source_len && length <= source_len - offset
}

pub fn serialize_compiled_program(
    compiled: &CompiledProgram,
    program_type: ast::ProgramType,
    source_hash: &[u8; SOURCE_HASH_SIZE],
) -> Vec<u8> {
    let mut encoder = Encoder::new();
    CacheBlob {
        compiled,
        program_type,
        source_hash,
    }
    .encode(&mut encoder);
    encoder.finish()
}

pub(crate) fn decode_blob(
    bytes: &[u8],
    expected_program_type: ast::ProgramType,
    expected_source_hash: &[u8; SOURCE_HASH_SIZE],
) -> Option<DecodedCacheBlob> {
    decode_blob_impl(bytes, expected_program_type, expected_source_hash, None)
}

pub(crate) type FreeBytecodeCacheBlobOwner = unsafe extern "C" fn(*mut c_void);
pub(crate) type CloneBytecodeCacheBlobOwner = unsafe extern "C" fn(*const c_void) -> *mut c_void;

pub(crate) struct ForeignBytecodeCacheBlobOwner {
    pub(crate) owner: *mut c_void,
    pub(crate) clone_owner: CloneBytecodeCacheBlobOwner,
    pub(crate) free_owner: FreeBytecodeCacheBlobOwner,
}

pub(crate) fn decode_blob_with_foreign_owner(
    bytes: &[u8],
    expected_program_type: ast::ProgramType,
    expected_source_hash: &[u8; SOURCE_HASH_SIZE],
    owner: ForeignBytecodeCacheBlobOwner,
) -> Option<DecodedCacheBlob> {
    decode_blob_impl(bytes, expected_program_type, expected_source_hash, Some(owner))
}

fn decode_blob_impl(
    bytes: &[u8],
    expected_program_type: ast::ProgramType,
    expected_source_hash: &[u8; SOURCE_HASH_SIZE],
    owner: Option<ForeignBytecodeCacheBlobOwner>,
) -> Option<DecodedCacheBlob> {
    let mut decoder = Decoder::new(bytes, owner);
    let blob = CacheBlob::decode(&mut decoder, expected_program_type, expected_source_hash)?;
    if !decoder.is_empty() {
        return None;
    }
    blob.validate();
    Some(blob)
}

struct Encoder {
    bytes: Vec<u8>,
}

impl Encoder {
    fn new() -> Self {
        Self { bytes: Vec::new() }
    }

    fn finish(self) -> Vec<u8> {
        self.bytes
    }

    fn byte(&mut self, value: u8) {
        self.bytes.push(value);
    }

    fn bytes(&mut self, bytes: &[u8]) {
        self.bytes.extend_from_slice(bytes);
    }

    fn align_to(&mut self, alignment: usize) {
        let padding = self.bytes.len().next_multiple_of(alignment) - self.bytes.len();
        self.bytes.extend(std::iter::repeat_n(0, padding));
    }

    fn align_bytes_payload_to(&mut self, alignment: usize) {
        let payload_offset = self.bytes.len() + size_of::<u32>();
        let padding = payload_offset.next_multiple_of(alignment) - payload_offset;
        self.bytes.extend(std::iter::repeat_n(0, padding));
    }

    fn sequence<T>(&mut self, items: &[T], mut encode_item: impl FnMut(&T, &mut Self)) {
        u32_from_usize(items.len()).encode(self);
        for item in items {
            encode_item(item, self);
        }
    }
}

struct ForeignBytecodeCacheBlob {
    data: *const u8,
    length: usize,
    owner: *mut c_void,
    clone_owner: CloneBytecodeCacheBlobOwner,
    free_owner: FreeBytecodeCacheBlobOwner,
}

impl Drop for ForeignBytecodeCacheBlob {
    fn drop(&mut self) {
        unsafe {
            (self.free_owner)(self.owner);
        }
    }
}

struct Decoder<'a> {
    bytes: &'a [u8],
    offset: usize,
    foreign_blob: Option<Rc<ForeignBytecodeCacheBlob>>,
}

impl<'a> Decoder<'a> {
    fn new(bytes: &'a [u8], owner: Option<ForeignBytecodeCacheBlobOwner>) -> Self {
        let foreign_blob = owner.map(|owner| {
            Rc::new(ForeignBytecodeCacheBlob {
                data: bytes.as_ptr(),
                length: bytes.len(),
                owner: owner.owner,
                clone_owner: owner.clone_owner,
                free_owner: owner.free_owner,
            })
        });
        Self {
            bytes,
            offset: 0,
            foreign_blob,
        }
    }

    fn is_empty(&self) -> bool {
        self.bytes.is_empty()
    }

    fn bytes(&mut self, length: usize) -> Option<&'a [u8]> {
        if self.bytes.len() < length {
            return None;
        }

        let (bytes, rest) = self.bytes.split_at(length);
        self.bytes = rest;
        self.offset = self.offset.checked_add(length)?;
        Some(bytes)
    }

    fn align_to(&mut self, alignment: usize) -> Option<()> {
        let padding = self.offset.next_multiple_of(alignment) - self.offset;
        self.bytes(padding)?;
        Some(())
    }

    fn align_bytes_payload_to(&mut self, alignment: usize) -> Option<()> {
        let payload_offset = self.offset.checked_add(size_of::<u32>())?;
        let padding = payload_offset.next_multiple_of(alignment) - payload_offset;
        self.bytes(padding)?;
        Some(())
    }

    fn bytecode_bytes(&mut self, length: usize) -> Option<DecodedBytecodeBytes> {
        let offset = self.offset;
        let bytes = self.bytes(length)?;
        if let Some(foreign_blob) = &self.foreign_blob {
            return Some(DecodedBytecodeBytes::Foreign {
                blob: foreign_blob.clone(),
                range: offset..offset + length,
            });
        }

        Some(DecodedBytecodeBytes::Owned(bytes.to_vec()))
    }

    fn expect_bytes(&mut self, expected: &[u8]) -> Option<()> {
        (self.bytes(expected.len())? == expected).then_some(())
    }

    fn sequence_values<T>(&mut self, mut decode_item: impl FnMut(&mut Self) -> Option<T>) -> Option<Vec<T>> {
        let length: usize = u32::decode(self)?.try_into().ok()?;
        // Reject lengths that cannot fit in the remaining blob even for one-byte items, so a
        // malformed sidecar with a four-billion element header cannot drag the allocator down.
        if length > self.bytes.len() {
            return None;
        }

        let mut values = Vec::with_capacity(length);
        for _ in 0..length {
            values.push(decode_item(self)?);
        }
        Some(values)
    }
}

trait Encode {
    fn encode(&self, encoder: &mut Encoder);
}

trait Decode: Sized {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self>;
}

impl Encode for bool {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.byte(*self as u8);
    }
}

impl Decode for bool {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(false),
            1 => Some(true),
            _ => None,
        }
    }
}

impl Encode for u8 {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.byte(*self);
    }
}

impl Decode for u8 {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        decoder.bytes(1)?.first().copied()
    }
}

impl Encode for u32 {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.bytes(&self.to_le_bytes());
    }
}

impl Decode for u32 {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(u32::from_le_bytes(decoder.bytes(4)?.try_into().ok()?))
    }
}

impl Encode for i32 {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.bytes(&self.to_le_bytes());
    }
}

impl Decode for i32 {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(i32::from_le_bytes(decoder.bytes(4)?.try_into().ok()?))
    }
}

impl Encode for u64 {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.bytes(&self.to_le_bytes());
    }
}

impl Decode for u64 {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(u64::from_le_bytes(decoder.bytes(8)?.try_into().ok()?))
    }
}

impl Encode for usize {
    fn encode(&self, encoder: &mut Encoder) {
        u64::try_from(*self).expect("usize does not fit in u64").encode(encoder);
    }
}

impl Decode for usize {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        u64::decode(decoder)?.try_into().ok()
    }
}

impl Encode for f64 {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.bytes(&self.to_le_bytes());
    }
}

impl Decode for f64 {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(f64::from_le_bytes(decoder.bytes(8)?.try_into().ok()?))
    }
}

impl Decode for ast::Position {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(Self {
            line: u32::decode(decoder)?,
            column: u32::decode(decoder)?,
            offset: u32::decode(decoder)?,
        })
    }
}

impl<T: Encode> Encode for Option<T> {
    fn encode(&self, encoder: &mut Encoder) {
        self.is_some().encode(encoder);
        if let Some(value) = self {
            value.encode(encoder);
        }
    }
}

impl<T: Decode> Decode for Option<T> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        if bool::decode(decoder)? {
            Some(Some(T::decode(decoder)?))
        } else {
            Some(None)
        }
    }
}

impl Decode for ast::Utf16String {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        decoder.align_to(align_of::<u16>())?;
        let length: usize = u32::decode(decoder)?.try_into().ok()?;
        let bytes = decoder.bytes(length.checked_mul(size_of::<u16>())?)?;
        let mut code_units = Vec::with_capacity(length);
        for chunk in bytes.chunks_exact(size_of::<u16>()) {
            code_units.push(u16::from_le_bytes(chunk.try_into().ok()?));
        }
        Some(code_units.into())
    }
}

enum DecodedUtf16String {
    Owned(ast::Utf16String),
    // The surrounding decoded executable keeps the mapped blob alive through its
    // DecodedBytecodeBytes. Store only the payload pointer here so large string
    // tables do not clone an owner handle for every string.
    Foreign { data: *const u16, length: usize },
}

impl Decode for DecodedUtf16String {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        decoder.align_to(align_of::<u16>())?;
        let length: usize = u32::decode(decoder)?.try_into().ok()?;
        let byte_length = length.checked_mul(size_of::<u16>())?;
        let bytes = decoder.bytes(byte_length)?;
        if decoder.foreign_blob.is_some() {
            debug_assert_eq!((bytes.as_ptr() as usize) % align_of::<u16>(), 0);
            return Some(Self::Foreign {
                data: bytes.as_ptr().cast(),
                length,
            });
        }

        let mut code_units = Vec::with_capacity(length);
        for chunk in bytes.chunks_exact(size_of::<u16>()) {
            code_units.push(u16::from_le_bytes(chunk.try_into().ok()?));
        }
        Some(Self::Owned(code_units.into()))
    }
}

impl From<ast::Utf16String> for DecodedUtf16String {
    fn from(value: ast::Utf16String) -> Self {
        Self::Owned(value)
    }
}

impl DecodedUtf16String {
    fn len(&self) -> usize {
        match self {
            Self::Owned(value) => value.len(),
            Self::Foreign { length, .. } => *length,
        }
    }

    fn to_vec(&self) -> Vec<u16> {
        match self {
            Self::Owned(value) => value.to_vec(),
            Self::Foreign { data, length } => unsafe {
                std::slice::from_raw_parts(*data, *length)
                    .iter()
                    .map(|code_unit| u16::from_le(*code_unit))
                    .collect()
            },
        }
    }

    fn to_utf16_string(&self) -> ast::Utf16String {
        self.to_vec().into()
    }
}

struct PreparedUtf16Slice {
    _storage: Option<Vec<u16>>,
    slice: FFIUtf16Slice,
}

impl PreparedUtf16Slice {
    fn new(value: &DecodedUtf16String) -> Self {
        match value {
            DecodedUtf16String::Owned(value) => Self {
                _storage: None,
                slice: FFIUtf16Slice::from(value.as_ref()),
            },
            DecodedUtf16String::Foreign { data, length } => {
                #[cfg(target_endian = "little")]
                {
                    Self {
                        _storage: None,
                        slice: FFIUtf16Slice {
                            data: *data,
                            length: *length,
                        },
                    }
                }
                #[cfg(not(target_endian = "little"))]
                {
                    let storage = value.to_vec();
                    let slice = FFIUtf16Slice::from(storage.as_slice());
                    Self {
                        _storage: Some(storage),
                        slice,
                    }
                }
            }
        }
    }

    fn as_ptr_len(&self) -> (*const u16, usize) {
        (self.slice.data, self.slice.length)
    }
}

fn utf16_slice_storage(strings: &[DecodedUtf16String]) -> (Vec<Vec<u16>>, Vec<FFIUtf16Slice>) {
    #[cfg(target_endian = "little")]
    let storage = Vec::new();
    #[cfg(not(target_endian = "little"))]
    let mut storage = Vec::new();
    let mut slices = Vec::with_capacity(strings.len());
    for string in strings {
        match string {
            DecodedUtf16String::Owned(value) => slices.push(FFIUtf16Slice::from(value.as_ref())),
            DecodedUtf16String::Foreign { data, length } => {
                #[cfg(target_endian = "little")]
                {
                    slices.push(FFIUtf16Slice {
                        data: *data,
                        length: *length,
                    });
                }
                #[cfg(not(target_endian = "little"))]
                {
                    storage.push(string.to_vec());
                    slices.push(FFIUtf16Slice::from(storage.last().unwrap().as_slice()));
                }
            }
        }
    }
    (storage, slices)
}

struct Bytes<'a>(&'a [u8]);

impl Encode for Bytes<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        u32_from_usize(self.0.len()).encode(encoder);
        encoder.bytes(self.0);
    }
}

struct ByteVector;

impl ByteVector {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<u8>> {
        let length: usize = u32::decode(decoder)?.try_into().ok()?;
        Some(decoder.bytes(length)?.to_vec())
    }
}

enum DecodedBytecodeBytes {
    Owned(Vec<u8>),
    Foreign {
        blob: Rc<ForeignBytecodeCacheBlob>,
        range: Range<usize>,
    },
}

impl DecodedBytecodeBytes {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        let length: usize = u32::decode(decoder)?.try_into().ok()?;
        decoder.bytecode_bytes(length)
    }

    fn as_slice(&self) -> &[u8] {
        match self {
            Self::Owned(bytes) => bytes,
            Self::Foreign { blob, range } => {
                debug_assert!(range.end <= blob.length);
                unsafe { std::slice::from_raw_parts(blob.data.add(range.start), range.len()) }
            }
        }
    }

    fn owner_for_ffi(&self) -> *mut c_void {
        match self {
            Self::Owned(_) => std::ptr::null_mut(),
            // The C++ executable retains the immutable blob so the hot
            // instruction stream can point directly into the cache file. Clone
            // the small owner wrapper here; the original decoded blob still
            // owns its copy until materialization finishes.
            Self::Foreign { blob, .. } => unsafe { (blob.clone_owner)(blob.owner.cast_const()) },
        }
    }

    fn len(&self) -> usize {
        self.as_slice().len()
    }

    fn decoder(&self) -> Decoder<'_> {
        match self {
            Self::Owned(bytes) => Decoder {
                bytes,
                offset: 0,
                foreign_blob: None,
            },
            Self::Foreign { blob, range } => Decoder {
                bytes: self.as_slice(),
                offset: range.start,
                foreign_blob: Some(blob.clone()),
            },
        }
    }
}

struct DecodedRecordSequence {
    count: usize,
    bytes: DecodedBytecodeBytes,
}

impl DecodedRecordSequence {
    fn encode<T>(encoder: &mut Encoder, items: &[T], mut encode_item: impl FnMut(&T, &mut Encoder)) {
        Self::encode_with_alignment(encoder, items, align_of::<u16>(), |item, encoder| {
            encode_item(item, encoder);
        });
    }

    fn encode_with_alignment<T>(
        encoder: &mut Encoder,
        items: &[T],
        alignment: usize,
        mut encode_item: impl FnMut(&T, &mut Encoder),
    ) {
        u32_from_usize(items.len()).encode(encoder);

        let mut payload_encoder = Encoder::new();
        for item in items {
            encode_item(item, &mut payload_encoder);
        }

        encoder.align_bytes_payload_to(alignment);
        Bytes(&payload_encoder.finish()).encode(encoder);
    }

    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Self::decode_with_alignment(decoder, align_of::<u16>())
    }

    fn decode_with_alignment(decoder: &mut Decoder<'_>, alignment: usize) -> Option<Self> {
        let count: usize = u32::decode(decoder)?.try_into().ok()?;
        decoder.align_bytes_payload_to(alignment)?;
        let byte_length: usize = u32::decode(decoder)?.try_into().ok()?;
        // Every record currently has at least one byte in the payload. Reject
        // impossible counts up front so corrupt cache files cannot ask later
        // materialization to reserve huge vectors for tiny payloads.
        if count > byte_length {
            return None;
        }
        Some(Self {
            count,
            bytes: decoder.bytecode_bytes(byte_length)?,
        })
    }

    fn len(&self) -> usize {
        self.count
    }

    fn decoder(&self) -> Decoder<'_> {
        self.bytes.decoder()
    }
}

struct Utf16<'a>(&'a [u16]);

impl Encode for Utf16<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.align_to(align_of::<u16>());
        u32_from_usize(self.0.len()).encode(encoder);
        for code_unit in self.0 {
            encoder.bytes(&code_unit.to_le_bytes());
        }
    }
}

struct CacheBlob<'a> {
    compiled: &'a CompiledProgram,
    program_type: ast::ProgramType,
    // Fingerprint of the decoded source text the blob was generated from. Cache writes happen asynchronously after the
    // HTTP response has been served, so the entry on disk may have been replaced for the same (URL, vary key) by the
    // time we go to attach the sidecar. Embedding the source hash makes a stale write harmless: a later read whose
    // source no longer matches will reject the blob and fall through to source compilation.
    source_hash: &'a [u8; SOURCE_HASH_SIZE],
}

impl Encode for CacheBlob<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.bytes(MAGIC);
        FORMAT_VERSION.encode(encoder);
        self.program_type.encode(encoder);
        encoder.bytes(self.source_hash);
        self.compiled.parsed.has_top_level_await.encode(encoder);
        self.compiled.parsed.is_strict_mode.encode(encoder);
        DeclarationMetadataRecord {
            compiled: self.compiled,
            program_type: self.program_type,
        }
        .encode(encoder);
        ProgramRecord::from(self.compiled).encode(encoder);
    }
}

impl CacheBlob<'_> {
    fn decode(
        decoder: &mut Decoder<'_>,
        expected_program_type: ast::ProgramType,
        expected_source_hash: &[u8; SOURCE_HASH_SIZE],
    ) -> Option<DecodedCacheBlob> {
        decoder.expect_bytes(MAGIC)?;
        (u32::decode(decoder)? == FORMAT_VERSION).then_some(())?;
        let program_type = ast::ProgramType::decode(decoder)?;
        (program_type == expected_program_type).then_some(())?;
        (decoder.bytes(SOURCE_HASH_SIZE)? == expected_source_hash).then_some(())?;
        Some(DecodedCacheBlob {
            program_type,
            has_top_level_await: bool::decode(decoder)?,
            is_strict_mode: bool::decode(decoder)?,
            metadata: DeclarationMetadataRecord::decode(decoder)?,
            program: ProgramRecord::decode(decoder)?,
        })
    }
}

pub(crate) struct DecodedCacheBlob {
    program_type: ast::ProgramType,
    has_top_level_await: bool,
    is_strict_mode: bool,
    metadata: DecodedDeclarationMetadata,
    program: DecodedProgramRecord,
}

impl DecodedCacheBlob {
    fn validate(&self) {
        let _ = self.program_type as u8;
        let _ = self.has_top_level_await || self.is_strict_mode;
        self.metadata.validate();
        self.program.validate();
    }

    pub(crate) fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.metadata.source_ranges_are_valid(source_len)
            && self.metadata.indices_are_valid()
            && self.program.source_ranges_are_valid(source_len)
            && self.program.indices_are_valid()
    }

    pub(crate) unsafe fn materialize_script(
        self,
        vm_ptr: *mut c_void,
        source_code_ptr: *const c_void,
        gdi_context: *mut c_void,
    ) -> *mut c_void {
        unsafe {
            let Self {
                program_type,
                is_strict_mode,
                metadata,
                program,
                ..
            } = self;
            if program_type != ast::ProgramType::Script {
                return std::ptr::null_mut();
            }
            let DecodedDeclarationMetadata::Script {
                metadata,
                declaration_functions,
            } = metadata
            else {
                return std::ptr::null_mut();
            };
            let ProgramKind::ScriptOrModule = program.kind else {
                return std::ptr::null_mut();
            };
            if declaration_functions.len() != metadata.function_names.len() {
                return std::ptr::null_mut();
            }

            if !materialize_script_declaration_metadata(
                metadata,
                declaration_functions,
                is_strict_mode,
                vm_ptr,
                source_code_ptr,
                gdi_context,
            ) {
                return std::ptr::null_mut();
            }
            materialize_executable(program.executable, vm_ptr, source_code_ptr)
        }
    }

    pub(crate) unsafe fn materialize_module(
        self,
        vm_ptr: *mut c_void,
        source_code_ptr: *const c_void,
        module_context: *mut c_void,
        callbacks: *const ModuleCallbacks,
        tla_executable_out: *mut *mut c_void,
    ) -> *mut c_void {
        unsafe {
            if callbacks.is_null() {
                return std::ptr::null_mut();
            }
            let cb = &*callbacks;
            let Self {
                program_type,
                has_top_level_await,
                metadata,
                program,
                ..
            } = self;
            if program_type != ast::ProgramType::Module {
                return std::ptr::null_mut();
            }
            let DecodedDeclarationMetadata::Module {
                metadata,
                declaration_functions,
            } = metadata
            else {
                return std::ptr::null_mut();
            };
            if declaration_functions.len() != metadata.function_names.len() {
                return std::ptr::null_mut();
            }

            (cb.set_has_top_level_await)(module_context, has_top_level_await);
            if !materialize_module_declaration_metadata(
                metadata,
                declaration_functions,
                vm_ptr,
                source_code_ptr,
                module_context,
                cb,
            ) {
                return std::ptr::null_mut();
            }

            match program.kind {
                ProgramKind::AsyncModule => {
                    let exec_ptr = materialize_executable(program.executable, vm_ptr, source_code_ptr);
                    if !tla_executable_out.is_null() {
                        *tla_executable_out = exec_ptr;
                    }
                    std::ptr::null_mut()
                }
                ProgramKind::ScriptOrModule => {
                    if !tla_executable_out.is_null() {
                        *tla_executable_out = std::ptr::null_mut();
                    }
                    materialize_executable(program.executable, vm_ptr, source_code_ptr)
                }
            }
        }
    }
}

unsafe fn materialize_script_declaration_metadata(
    metadata: ScriptDeclarationMetadata,
    declaration_functions: Vec<DecodedFunctionRecord>,
    is_strict_mode: bool,
    vm_ptr: *mut c_void,
    source_code_ptr: *const c_void,
    gdi_context: *mut c_void,
) -> bool {
    unsafe {
        use crate::bytecode::ffi::{
            script_gdi_push_annex_b_name, script_gdi_push_function, script_gdi_push_lexical_binding,
            script_gdi_push_lexical_name, script_gdi_push_var_name, script_gdi_push_var_scoped_name,
        };

        for name in &metadata.lexical_names {
            script_gdi_push_lexical_name(gdi_context, name.as_ptr(), name.len());
        }
        for name in &metadata.var_names {
            script_gdi_push_var_name(gdi_context, name.as_ptr(), name.len());
        }
        for (function, name) in declaration_functions.into_iter().zip(metadata.function_names.iter()) {
            let sfd_ptr = materialize_function(function, is_strict_mode, vm_ptr, source_code_ptr);
            if sfd_ptr.is_null() {
                return false;
            }
            script_gdi_push_function(gdi_context, sfd_ptr, name.as_ptr(), name.len());
        }
        for name in &metadata.var_scoped_names {
            script_gdi_push_var_scoped_name(gdi_context, name.as_ptr(), name.len());
        }
        for name in &metadata.annex_b_candidate_names {
            script_gdi_push_annex_b_name(gdi_context, name.as_ptr(), name.len());
        }
        for binding in &metadata.lexical_bindings {
            script_gdi_push_lexical_binding(
                gdi_context,
                binding.name.as_ptr(),
                binding.name.len(),
                binding.is_constant,
            );
        }

        true
    }
}

unsafe fn materialize_module_declaration_metadata(
    metadata: ModuleDeclarationMetadata,
    declaration_functions: Vec<DecodedFunctionRecord>,
    vm_ptr: *mut c_void,
    source_code_ptr: *const c_void,
    module_context: *mut c_void,
    cb: &ModuleCallbacks,
) -> bool {
    unsafe {
        for entry in &metadata.import_entries {
            let (import_name, import_name_len, is_namespace) = entry
                .import_name
                .as_ref()
                .map(|name| (name.as_ptr(), name.len(), false))
                .unwrap_or((std::ptr::null(), 0, true));
            let attributes = import_attributes_to_ffi(&entry.module_request.attributes);
            (cb.push_import_entry)(
                module_context,
                import_name,
                import_name_len,
                is_namespace,
                entry.local_name.as_ptr(),
                entry.local_name.len(),
                entry.module_request.specifier.as_ptr(),
                entry.module_request.specifier.len(),
                attributes.keys.as_ptr(),
                attributes.values.as_ptr(),
                attributes.keys.len(),
            );
        }

        for entry in &metadata.local_exports {
            push_module_export_entry(module_context, cb.push_local_export, entry);
        }
        for entry in &metadata.indirect_exports {
            push_module_export_entry(module_context, cb.push_indirect_export, entry);
        }
        for entry in &metadata.star_exports {
            push_module_export_entry(module_context, cb.push_star_export, entry);
        }
        for request in &metadata.requested_modules {
            let attributes = import_attributes_to_ffi(&request.attributes);
            (cb.push_requested_module)(
                module_context,
                request.specifier.as_ptr(),
                request.specifier.len(),
                attributes.keys.as_ptr(),
                attributes.values.as_ptr(),
                attributes.keys.len(),
            );
        }
        if let Some(name) = &metadata.default_export_binding_name {
            (cb.set_default_export_binding)(module_context, name.as_ptr(), name.len());
        }
        for name in &metadata.var_declared_names {
            (cb.push_var_name)(module_context, name.as_ptr(), name.len());
        }
        for (function, name) in declaration_functions.into_iter().zip(metadata.function_names.iter()) {
            let sfd_ptr = materialize_function(function, true, vm_ptr, source_code_ptr);
            if sfd_ptr.is_null() {
                return false;
            }
            (cb.push_function)(module_context, sfd_ptr, name.as_ptr(), name.len());
        }
        for binding in &metadata.lexical_bindings {
            (cb.push_lexical_binding)(
                module_context,
                binding.name.as_ptr(),
                binding.name.len(),
                binding.is_constant,
                binding.function_index,
            );
        }

        true
    }
}

struct ImportAttributesFfi {
    keys: Vec<FFIUtf16Slice>,
    values: Vec<FFIUtf16Slice>,
}

fn import_attributes_to_ffi(attributes: &[ast::ImportAttribute]) -> ImportAttributesFfi {
    ImportAttributesFfi {
        keys: attributes
            .iter()
            .map(|attribute| FFIUtf16Slice::from(attribute.key.as_ref()))
            .collect(),
        values: attributes
            .iter()
            .map(|attribute| FFIUtf16Slice::from(attribute.value.as_ref()))
            .collect(),
    }
}

unsafe fn push_module_export_entry(
    module_context: *mut c_void,
    callback: crate::ModuleExportEntryCallback,
    entry: &ModuleExportEntryRecord,
) {
    unsafe {
        let (export_name, export_name_len) = entry
            .export_name
            .as_ref()
            .map(|name| (name.as_ptr(), name.len()))
            .unwrap_or((std::ptr::null(), 0));
        let (local_or_import_name, local_or_import_name_len) = entry
            .local_or_import_name
            .as_ref()
            .map(|name| (name.as_ptr(), name.len()))
            .unwrap_or((std::ptr::null(), 0));
        let (module_specifier, module_specifier_len, attributes) = entry
            .module_request
            .as_ref()
            .map(|request| {
                (
                    request.specifier.as_ptr(),
                    request.specifier.len(),
                    import_attributes_to_ffi(&request.attributes),
                )
            })
            .unwrap_or((
                std::ptr::null(),
                0,
                ImportAttributesFfi {
                    keys: Vec::new(),
                    values: Vec::new(),
                },
            ));

        callback(
            module_context,
            entry.kind as u8,
            export_name,
            export_name_len,
            local_or_import_name,
            local_or_import_name_len,
            module_specifier,
            module_specifier_len,
            attributes.keys.as_ptr(),
            attributes.values.as_ptr(),
            attributes.keys.len(),
        );
    }
}

unsafe fn materialize_function(
    function: DecodedFunctionRecord,
    outer_strict: bool,
    vm_ptr: *mut c_void,
    source_code_ptr: *const c_void,
) -> *mut c_void {
    unsafe {
        if function.precompiled.validate_cached_bytecode().is_err() {
            return std::ptr::null_mut();
        }

        let (_parameter_name_storage, parameter_names): (Vec<Vec<u16>>, Vec<FFIUtf16Slice>) = function
            .parameter_names
            .as_ref()
            .map(|names| utf16_slice_storage(names))
            .unwrap_or_default();
        let name_storage = function.name.as_ref().map(PreparedUtf16Slice::new);
        let (name, name_len) = name_storage
            .as_ref()
            .map(PreparedUtf16Slice::as_ptr_len)
            .unwrap_or((std::ptr::null(), 0));
        let source_text_offset = function.source_text_start as usize;
        let source_text_length = function
            .source_text_end
            .checked_sub(function.source_text_start)
            .map(|length| length as usize)
            .unwrap_or(0);

        let data = FFISharedFunctionData {
            name,
            name_len,
            function_kind: function.kind as u8,
            function_length: function.function_length,
            formal_parameter_count: function.formal_parameter_count,
            strict: function.is_strict_mode || outer_strict,
            is_arrow: function.is_arrow_function,
            has_simple_parameter_list: function.parameter_names.is_some(),
            parameter_names: parameter_names.as_ptr(),
            parameter_name_count: parameter_names.len(),
            source_text_offset,
            source_text_length,
            rust_function_ast: std::ptr::null_mut(),
            uses_this: function.uses_this,
            uses_this_from_environment: function.uses_this_from_environment,
        };

        let sfd_ptr = crate::bytecode::ffi::rust_create_sfd(vm_ptr, source_code_ptr, &raw const data);
        if sfd_ptr.is_null() {
            return std::ptr::null_mut();
        }

        if let Some((name, is_private)) = &function.class_field_initializer_name {
            let name_storage = PreparedUtf16Slice::new(name);
            let (name, name_len) = name_storage.as_ptr_len();
            crate::bytecode::ffi::rust_sfd_set_class_field_initializer_name(sfd_ptr, name, name_len, *is_private);
        }

        let cached_executable_ptr = Box::into_raw(Box::new(function.precompiled)) as *mut c_void;
        crate::bytecode::ffi::rust_sfd_set_cached_bytecode_executable(
            sfd_ptr,
            cached_executable_ptr,
            function.metadata.uses_this,
            function.metadata.this_value_needs_environment_resolution,
            function.metadata.function_environment_needed,
            function.metadata.function_environment_bindings_count,
            function.metadata.var_environment_bindings_count,
            function.metadata.might_need_arguments,
            function.metadata.contains_eval,
        );

        sfd_ptr
    }
}

pub(crate) unsafe fn materialize_cached_function(
    cached_executable_ptr: *mut c_void,
    vm_ptr: *mut c_void,
    source_code_ptr: *const c_void,
) -> *mut c_void {
    unsafe {
        if cached_executable_ptr.is_null() {
            return std::ptr::null_mut();
        }
        let cached_executable = Box::from_raw(cached_executable_ptr as *mut DecodedCachedExecutableRecord);
        let Some(executable) = cached_executable.decode_executable() else {
            return std::ptr::null_mut();
        };
        if executable.validate_cached_bytecode().is_err() {
            return std::ptr::null_mut();
        }
        materialize_executable(executable, vm_ptr, source_code_ptr)
    }
}

pub(crate) unsafe fn free_cached_function(cached_executable_ptr: *mut c_void) {
    unsafe {
        if !cached_executable_ptr.is_null() {
            drop(Box::from_raw(
                cached_executable_ptr as *mut DecodedCachedExecutableRecord,
            ));
        }
    }
}

unsafe fn materialize_executable(
    executable: DecodedExecutableRecord,
    vm_ptr: *mut c_void,
    source_code_ptr: *const c_void,
) -> *mut c_void {
    unsafe {
        let DecodedExecutableRecord {
            strict,
            number_of_registers,
            number_of_arguments,
            cache_counters,
            this_value_needs_environment_resolution,
            length_identifier,
            bytecode,
            identifier_table,
            property_key_table,
            string_table,
            constants,
            exception_handlers,
            source_map,
            local_variables,
            shared_functions,
            class_blueprints,
        } = executable;

        let mut generator = Generator::new();
        generator.strict = strict;
        generator.this_value_needs_environment_resolution = this_value_needs_environment_resolution;
        generator.next_property_lookup_cache = cache_counters.property_lookup_cache_count;
        generator.next_global_variable_cache = cache_counters.global_variable_cache_count;
        generator.next_template_object_cache = cache_counters.template_object_cache_count;
        generator.next_object_shape_cache = cache_counters.object_shape_cache_count;
        generator.next_object_property_iterator_cache = cache_counters.object_property_iterator_cache_count;
        let Some(identifier_table) = identifier_table.into_values() else {
            return std::ptr::null_mut();
        };
        generator.identifier_table = identifier_table
            .into_iter()
            .map(|value| value.to_utf16_string())
            .collect();
        let Some(property_key_table) = property_key_table.into_values() else {
            return std::ptr::null_mut();
        };
        generator.property_key_table = property_key_table
            .into_iter()
            .map(|value| value.to_utf16_string())
            .collect();
        let Some(string_table) = string_table.into_values() else {
            return std::ptr::null_mut();
        };
        generator.string_table = string_table.into_iter().map(|value| value.to_utf16_string()).collect();
        let Some(constants) = constants.into_constant_values() else {
            return std::ptr::null_mut();
        };
        generator.constants = constants;
        let Some(local_variables) = local_variables.into_values() else {
            return std::ptr::null_mut();
        };
        generator.local_variables = local_variables
            .into_iter()
            .map(DecodedLocalVariable::into_local_variable)
            .collect();
        generator.length_identifier = length_identifier.map(PropertyKeyTableIndex);

        let Some(shared_functions) = shared_functions.into_values() else {
            return std::ptr::null_mut();
        };
        let sfd_ptrs: Vec<*const c_void> = shared_functions
            .into_iter()
            .map(|function| materialize_function(function, generator.strict, vm_ptr, source_code_ptr) as *const c_void)
            .collect();
        if sfd_ptrs.iter().any(|ptr| ptr.is_null()) {
            return std::ptr::null_mut();
        }

        let Some(class_blueprints) = class_blueprints.into_values() else {
            return std::ptr::null_mut();
        };
        let class_blueprints: Vec<PendingClassBlueprint> =
            class_blueprints.into_iter().map(PendingClassBlueprint::from).collect();
        let bp_ptrs: Vec<*mut c_void> = class_blueprints
            .iter()
            .map(|blueprint| crate::bytecode::ffi::materialize_class_blueprint(blueprint, vm_ptr, source_code_ptr))
            .collect();
        if bp_ptrs.iter().any(|ptr| ptr.is_null()) {
            return std::ptr::null_mut();
        }
        let Some(exception_handlers) = exception_handlers.into_values() else {
            return std::ptr::null_mut();
        };
        let Some(source_map) = source_map.into_values() else {
            return std::ptr::null_mut();
        };

        crate::bytecode::ffi::create_executable_with_dependencies_from_parts(
            &generator,
            crate::bytecode::ffi::ExecutableParts {
                bytecode: bytecode.as_slice(),
                bytecode_owner: bytecode.owner_for_ffi(),
                exception_handlers: &exception_handlers,
                source_map: &source_map,
                basic_block_start_offsets: &[],
                number_of_registers,
                number_of_arguments,
            },
            vm_ptr,
            source_code_ptr,
            &sfd_ptrs,
            &bp_ptrs,
        )
    }
}

impl Encode for ast::ProgramType {
    fn encode(&self, encoder: &mut Encoder) {
        (*self as u8).encode(encoder);
    }
}

impl Decode for ast::ProgramType {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::Script),
            1 => Some(Self::Module),
            _ => None,
        }
    }
}

impl Decode for ast::ExportEntryKind {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::NamedExport),
            1 => Some(Self::ModuleRequestAll),
            2 => Some(Self::ModuleRequestAllButDefault),
            _ => None,
        }
    }
}

impl Decode for ast::FunctionKind {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::Normal),
            1 => Some(Self::Generator),
            2 => Some(Self::Async),
            3 => Some(Self::AsyncGenerator),
            _ => None,
        }
    }
}

struct DeclarationMetadataRecord<'a> {
    compiled: &'a CompiledProgram,
    program_type: ast::ProgramType,
}

impl Encode for DeclarationMetadataRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        let ast::StatementKind::Program(program) = &self.compiled.parsed.program.inner else {
            unreachable!("bytecode cache expects a parsed program root");
        };
        let arena = &self.compiled.parsed.arena;
        let scope = &arena.scopes[program.scope];
        match self.program_type {
            ast::ProgramType::Script => ScriptDeclarationMetadata::from_scope(scope, arena).encode(encoder),
            ast::ProgramType::Module => ModuleDeclarationMetadata::from_scope(scope, arena).encode(encoder),
        }
        DeclarationFunctionTable(&self.compiled.declaration_functions).encode(encoder);
    }
}

impl DeclarationMetadataRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedDeclarationMetadata> {
        match MetadataKind::decode(decoder)? {
            MetadataKind::Script => Some(DecodedDeclarationMetadata::Script {
                metadata: ScriptDeclarationMetadata::decode_payload(decoder)?,
                declaration_functions: DeclarationFunctionTable::decode(decoder)?,
            }),
            MetadataKind::Module => Some(DecodedDeclarationMetadata::Module {
                metadata: ModuleDeclarationMetadata::decode_payload(decoder)?,
                declaration_functions: DeclarationFunctionTable::decode(decoder)?,
            }),
        }
    }
}

enum DecodedDeclarationMetadata {
    Script {
        metadata: ScriptDeclarationMetadata,
        declaration_functions: Vec<DecodedFunctionRecord>,
    },
    Module {
        metadata: ModuleDeclarationMetadata,
        declaration_functions: Vec<DecodedFunctionRecord>,
    },
}

impl DecodedDeclarationMetadata {
    fn validate(&self) {
        match self {
            Self::Script {
                metadata,
                declaration_functions,
            } => {
                metadata.validate();
                for function in declaration_functions {
                    function.validate();
                }
            }
            Self::Module {
                metadata,
                declaration_functions,
            } => {
                metadata.validate();
                for function in declaration_functions {
                    function.validate();
                }
            }
        }
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        match self {
            Self::Script {
                declaration_functions, ..
            }
            | Self::Module {
                declaration_functions, ..
            } => declaration_functions
                .iter()
                .all(|function| function.source_ranges_are_valid(source_len)),
        }
    }

    fn indices_are_valid(&self) -> bool {
        match self {
            Self::Script { .. } => true,
            Self::Module {
                metadata,
                declaration_functions,
            } => {
                declaration_functions.len() == metadata.function_names.len()
                    && metadata.lexical_bindings.iter().all(|binding| {
                        binding.function_index < 0
                            || usize::try_from(binding.function_index)
                                .is_ok_and(|index| index < declaration_functions.len())
                    })
            }
        }
    }
}

#[repr(u8)]
#[derive(Clone, Copy)]
enum MetadataKind {
    Script = 0,
    Module = 1,
}

impl Encode for MetadataKind {
    fn encode(&self, encoder: &mut Encoder) {
        (*self as u8).encode(encoder);
    }
}

impl Decode for MetadataKind {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::Script),
            1 => Some(Self::Module),
            _ => None,
        }
    }
}

struct ScriptDeclarationMetadata {
    lexical_names: Vec<ast::Utf16String>,
    var_names: Vec<ast::Utf16String>,
    function_names: Vec<ast::Utf16String>,
    var_scoped_names: Vec<ast::Utf16String>,
    annex_b_candidate_names: Vec<ast::Utf16String>,
    lexical_bindings: Vec<LexicalBindingRecord>,
}

impl ScriptDeclarationMetadata {
    fn from_scope(scope: &ast::ScopeData, arena: &ast::AstArena) -> Self {
        let mut metadata = Self {
            lexical_names: Vec::new(),
            var_names: Vec::new(),
            function_names: script_function_names(scope, arena),
            var_scoped_names: Vec::new(),
            annex_b_candidate_names: scope.annexb_function_names.to_vec(),
            lexical_bindings: Vec::new(),
        };

        for child in &scope.children {
            collect_var_names_recursive(&child.inner, arena, &mut metadata.var_names);
            if let ast::StatementKind::FunctionDeclaration(ref function) = child.inner
                && let Some(name) = function.name
            {
                metadata.var_names.push(arena.name_of(name).clone());
            }
            collect_script_lexical_names(&child.inner, arena, &mut metadata.lexical_names);
            collect_script_lexical_bindings(&child.inner, arena, &mut metadata.lexical_bindings);
            collect_var_names_recursive(&child.inner, arena, &mut metadata.var_scoped_names);
        }

        metadata
    }

    fn decode_payload(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(Self {
            lexical_names: Utf16Vector::decode(decoder)?,
            var_names: Utf16Vector::decode(decoder)?,
            function_names: Utf16Vector::decode(decoder)?,
            var_scoped_names: Utf16Vector::decode(decoder)?,
            annex_b_candidate_names: Utf16Vector::decode(decoder)?,
            lexical_bindings: LexicalBindingTable::decode(decoder)?,
        })
    }

    fn validate(&self) {
        let _ = self.lexical_names.len()
            + self.var_names.len()
            + self.function_names.len()
            + self.var_scoped_names.len()
            + self.annex_b_candidate_names.len()
            + self.lexical_bindings.len();
    }
}

impl Encode for ScriptDeclarationMetadata {
    fn encode(&self, encoder: &mut Encoder) {
        MetadataKind::Script.encode(encoder);
        Utf16Vector(&self.lexical_names).encode(encoder);
        Utf16Vector(&self.var_names).encode(encoder);
        Utf16Vector(&self.function_names).encode(encoder);
        Utf16Vector(&self.var_scoped_names).encode(encoder);
        Utf16Vector(&self.annex_b_candidate_names).encode(encoder);
        LexicalBindingTable(&self.lexical_bindings).encode(encoder);
    }
}

struct ModuleDeclarationMetadata {
    import_entries: Vec<ModuleImportEntryRecord>,
    local_exports: Vec<ModuleExportEntryRecord>,
    indirect_exports: Vec<ModuleExportEntryRecord>,
    star_exports: Vec<ModuleExportEntryRecord>,
    requested_modules: Vec<ModuleRequestRecord>,
    default_export_binding_name: Option<ast::Utf16String>,
    var_declared_names: Vec<ast::Utf16String>,
    function_names: Vec<ast::Utf16String>,
    lexical_bindings: Vec<ModuleLexicalBindingRecord>,
}

impl ModuleDeclarationMetadata {
    fn from_scope(scope: &ast::ScopeData, arena: &ast::AstArena) -> Self {
        let mut metadata = Self {
            import_entries: Vec::new(),
            local_exports: Vec::new(),
            indirect_exports: Vec::new(),
            star_exports: Vec::new(),
            requested_modules: requested_modules(scope),
            default_export_binding_name: None,
            var_declared_names: Vec::new(),
            function_names: Vec::new(),
            lexical_bindings: Vec::new(),
        };

        collect_module_imports_and_exports(scope, &mut metadata);

        let mut function_index = 0;
        for child in &scope.children {
            collect_module_var_names(&child.inner, arena, &mut metadata.var_declared_names);

            let (declaration, is_exported) = match &child.inner {
                ast::StatementKind::Export(export_data) => {
                    if let Some(ref statement) = export_data.statement {
                        (&statement.inner, true)
                    } else {
                        continue;
                    }
                }
                other => (other, false),
            };
            collect_module_declaration(declaration, is_exported, function_index, arena, &mut metadata);
            if matches!(declaration, ast::StatementKind::FunctionDeclaration(_)) {
                function_index += 1;
            }
        }

        metadata
    }

    fn decode_payload(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(Self {
            import_entries: ModuleImportEntryTable::decode(decoder)?,
            local_exports: ModuleExportEntryTable::decode(decoder)?,
            indirect_exports: ModuleExportEntryTable::decode(decoder)?,
            star_exports: ModuleExportEntryTable::decode(decoder)?,
            requested_modules: ModuleRequestTable::decode(decoder)?,
            default_export_binding_name: Option::<ast::Utf16String>::decode(decoder)?,
            var_declared_names: Utf16Vector::decode(decoder)?,
            function_names: Utf16Vector::decode(decoder)?,
            lexical_bindings: ModuleLexicalBindingTable::decode(decoder)?,
        })
    }

    fn validate(&self) {
        let _ = self.import_entries.len()
            + self.local_exports.len()
            + self.indirect_exports.len()
            + self.star_exports.len()
            + self.requested_modules.len()
            + self.var_declared_names.len()
            + self.function_names.len()
            + self.lexical_bindings.len();
        let _ = self
            .default_export_binding_name
            .as_ref()
            .map(|name| name.as_slice().len());
    }
}

impl Encode for ModuleDeclarationMetadata {
    fn encode(&self, encoder: &mut Encoder) {
        MetadataKind::Module.encode(encoder);
        ModuleImportEntryTable(&self.import_entries).encode(encoder);
        ModuleExportEntryTable(&self.local_exports).encode(encoder);
        ModuleExportEntryTable(&self.indirect_exports).encode(encoder);
        ModuleExportEntryTable(&self.star_exports).encode(encoder);
        ModuleRequestTable(&self.requested_modules).encode(encoder);
        self.default_export_binding_name
            .as_ref()
            .map(|name| Utf16(name))
            .encode(encoder);
        Utf16Vector(&self.var_declared_names).encode(encoder);
        Utf16Vector(&self.function_names).encode(encoder);
        ModuleLexicalBindingTable(&self.lexical_bindings).encode(encoder);
    }
}

struct Utf16Vector<'a>(&'a [ast::Utf16String]);

impl Encode for Utf16Vector<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |value, encoder| Utf16(value).encode(encoder));
    }
}

impl Utf16Vector<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ast::Utf16String>> {
        decoder.sequence_values(ast::Utf16String::decode)
    }
}

struct LexicalBindingRecord {
    name: ast::Utf16String,
    is_constant: bool,
}

impl Encode for LexicalBindingRecord {
    fn encode(&self, encoder: &mut Encoder) {
        Utf16(&self.name).encode(encoder);
        self.is_constant.encode(encoder);
    }
}

struct LexicalBindingTable<'a>(&'a [LexicalBindingRecord]);

impl Encode for LexicalBindingTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |binding, encoder| binding.encode(encoder));
    }
}

impl LexicalBindingTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<LexicalBindingRecord>> {
        decoder.sequence_values(|decoder| {
            Some(LexicalBindingRecord {
                name: ast::Utf16String::decode(decoder)?,
                is_constant: bool::decode(decoder)?,
            })
        })
    }
}

struct ModuleLexicalBindingRecord {
    name: ast::Utf16String,
    is_constant: bool,
    function_index: i32,
}

impl Encode for ModuleLexicalBindingRecord {
    fn encode(&self, encoder: &mut Encoder) {
        Utf16(&self.name).encode(encoder);
        self.is_constant.encode(encoder);
        self.function_index.encode(encoder);
    }
}

struct ModuleLexicalBindingTable<'a>(&'a [ModuleLexicalBindingRecord]);

impl Encode for ModuleLexicalBindingTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |binding, encoder| binding.encode(encoder));
    }
}

impl ModuleLexicalBindingTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ModuleLexicalBindingRecord>> {
        decoder.sequence_values(|decoder| {
            Some(ModuleLexicalBindingRecord {
                name: ast::Utf16String::decode(decoder)?,
                is_constant: bool::decode(decoder)?,
                function_index: i32::decode(decoder)?,
            })
        })
    }
}

#[derive(Clone)]
struct ModuleRequestRecord {
    specifier: ast::Utf16String,
    attributes: Vec<ast::ImportAttribute>,
}

impl From<&ast::ModuleRequest> for ModuleRequestRecord {
    fn from(request: &ast::ModuleRequest) -> Self {
        Self {
            specifier: request.module_specifier.clone(),
            attributes: request.attributes.clone(),
        }
    }
}

impl Encode for ModuleRequestRecord {
    fn encode(&self, encoder: &mut Encoder) {
        Utf16(&self.specifier).encode(encoder);
        ImportAttributeTable(&self.attributes).encode(encoder);
    }
}

impl Decode for ModuleRequestRecord {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(Self {
            specifier: ast::Utf16String::decode(decoder)?,
            attributes: ImportAttributeTable::decode(decoder)?,
        })
    }
}

struct ModuleRequestTable<'a>(&'a [ModuleRequestRecord]);

impl Encode for ModuleRequestTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |request, encoder| request.encode(encoder));
    }
}

impl ModuleRequestTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ModuleRequestRecord>> {
        decoder.sequence_values(ModuleRequestRecord::decode)
    }
}

struct ImportAttributeTable<'a>(&'a [ast::ImportAttribute]);

impl Encode for ImportAttributeTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |attribute, encoder| {
            Utf16(&attribute.key).encode(encoder);
            Utf16(&attribute.value).encode(encoder);
        });
    }
}

impl ImportAttributeTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ast::ImportAttribute>> {
        decoder.sequence_values(|decoder| {
            Some(ast::ImportAttribute {
                key: ast::Utf16String::decode(decoder)?,
                value: ast::Utf16String::decode(decoder)?,
            })
        })
    }
}

struct ModuleImportEntryRecord {
    import_name: Option<ast::Utf16String>,
    local_name: ast::Utf16String,
    module_request: ModuleRequestRecord,
}

impl Encode for ModuleImportEntryRecord {
    fn encode(&self, encoder: &mut Encoder) {
        self.import_name.as_ref().map(|name| Utf16(name)).encode(encoder);
        Utf16(&self.local_name).encode(encoder);
        self.module_request.encode(encoder);
    }
}

struct ModuleImportEntryTable<'a>(&'a [ModuleImportEntryRecord]);

impl Encode for ModuleImportEntryTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |entry, encoder| entry.encode(encoder));
    }
}

impl ModuleImportEntryTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ModuleImportEntryRecord>> {
        decoder.sequence_values(|decoder| {
            Some(ModuleImportEntryRecord {
                import_name: Option::<ast::Utf16String>::decode(decoder)?,
                local_name: ast::Utf16String::decode(decoder)?,
                module_request: ModuleRequestRecord::decode(decoder)?,
            })
        })
    }
}

struct ModuleExportEntryRecord {
    kind: ast::ExportEntryKind,
    export_name: Option<ast::Utf16String>,
    local_or_import_name: Option<ast::Utf16String>,
    module_request: Option<ModuleRequestRecord>,
}

impl Encode for ModuleExportEntryRecord {
    fn encode(&self, encoder: &mut Encoder) {
        (self.kind as u8).encode(encoder);
        self.export_name.as_ref().map(|name| Utf16(name)).encode(encoder);
        self.local_or_import_name
            .as_ref()
            .map(|name| Utf16(name))
            .encode(encoder);
        self.module_request.encode(encoder);
    }
}

struct ModuleExportEntryTable<'a>(&'a [ModuleExportEntryRecord]);

impl Encode for ModuleExportEntryTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        encoder.sequence(self.0, |entry, encoder| entry.encode(encoder));
    }
}

impl ModuleExportEntryTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<ModuleExportEntryRecord>> {
        decoder.sequence_values(|decoder| {
            Some(ModuleExportEntryRecord {
                kind: ast::ExportEntryKind::decode(decoder)?,
                export_name: Option::<ast::Utf16String>::decode(decoder)?,
                local_or_import_name: Option::<ast::Utf16String>::decode(decoder)?,
                module_request: Option::<ModuleRequestRecord>::decode(decoder)?,
            })
        })
    }
}

fn collect_script_lexical_names(
    statement: &ast::StatementKind,
    arena: &ast::AstArena,
    names: &mut Vec<ast::Utf16String>,
) {
    match statement {
        ast::StatementKind::VariableDeclaration(declaration) if declaration.kind != ast::DeclarationKind::Var => {
            for declarator in &declaration.declarations {
                for_each_bound_name(&declarator.target, arena, &mut |name| names.push(name.to_vec().into()));
            }
        }
        ast::StatementKind::UsingDeclaration(declarations) => {
            for declarator in declarations.iter() {
                for_each_bound_name(&declarator.target, arena, &mut |name| names.push(name.to_vec().into()));
            }
        }
        ast::StatementKind::ClassDeclaration(class_data) => {
            if let Some(name) = class_data.name {
                names.push(arena.name_of(name).clone());
            }
        }
        _ => {}
    }
}

fn collect_script_lexical_bindings(
    statement: &ast::StatementKind,
    arena: &ast::AstArena,
    bindings: &mut Vec<LexicalBindingRecord>,
) {
    match statement {
        ast::StatementKind::VariableDeclaration(declaration) if declaration.kind != ast::DeclarationKind::Var => {
            let is_constant = declaration.kind == ast::DeclarationKind::Const;
            for declarator in &declaration.declarations {
                for_each_bound_name(&declarator.target, arena, &mut |name| {
                    bindings.push(LexicalBindingRecord {
                        name: name.to_vec().into(),
                        is_constant,
                    });
                });
            }
        }
        ast::StatementKind::UsingDeclaration(declarations) => {
            for declarator in declarations.iter() {
                for_each_bound_name(&declarator.target, arena, &mut |name| {
                    bindings.push(LexicalBindingRecord {
                        name: name.to_vec().into(),
                        is_constant: false,
                    });
                });
            }
        }
        ast::StatementKind::ClassDeclaration(class_data) => {
            if let Some(name) = class_data.name {
                bindings.push(LexicalBindingRecord {
                    name: arena.name_of(name).clone(),
                    is_constant: false,
                });
            }
        }
        _ => {}
    }
}

fn script_function_names(scope: &ast::ScopeData, arena: &ast::AstArena) -> Vec<ast::Utf16String> {
    let mut last_position = HashMap::new();
    for (index, child) in scope.children.iter().enumerate() {
        if let ast::StatementKind::FunctionDeclaration(ref function) = child.inner
            && let Some(name) = function.name
        {
            last_position.insert(arena.identifiers[name].name, index);
        }
    }

    let mut names = Vec::new();
    for (index, child) in scope.children.iter().enumerate() {
        if let ast::StatementKind::FunctionDeclaration(ref function) = child.inner
            && let Some(name) = function.name
            && last_position.get(&arena.identifiers[name].name).copied() == Some(index)
        {
            names.push(arena.name_of(name).clone());
        }
    }
    names
}

fn collect_module_imports_and_exports(scope: &ast::ScopeData, metadata: &mut ModuleDeclarationMetadata) {
    struct ImportEntryWithRequest {
        import_name: Option<ast::Utf16String>,
        local_name: ast::Utf16String,
        module_request: ModuleRequestRecord,
    }

    let mut all_import_entries = Vec::new();

    for child in &scope.children {
        if let ast::StatementKind::Import(import_data) = &child.inner {
            for entry in &import_data.entries {
                let module_request = ModuleRequestRecord::from(&import_data.module_request);
                metadata.import_entries.push(ModuleImportEntryRecord {
                    import_name: entry.import_name.clone(),
                    local_name: entry.local_name.clone(),
                    module_request: module_request.clone(),
                });
                all_import_entries.push(ImportEntryWithRequest {
                    import_name: entry.import_name.clone(),
                    local_name: entry.local_name.clone(),
                    module_request,
                });
            }
        }
    }

    for child in &scope.children {
        let ast::StatementKind::Export(export_data) = &child.inner else {
            continue;
        };

        if export_data.is_default_export && export_data.entries.len() == 1 {
            let entry = &export_data.entries[0];
            let is_declaration = export_data.statement.as_ref().is_some_and(|statement| {
                matches!(
                    statement.inner,
                    ast::StatementKind::FunctionDeclaration(_) | ast::StatementKind::ClassDeclaration(_)
                )
            });
            let is_specific_import_export = all_import_entries.iter().any(|import| {
                entry.local_or_import_name.as_ref() == Some(&import.local_name) && import.import_name.is_some()
            });
            if !is_declaration && !is_specific_import_export {
                metadata.default_export_binding_name = entry.local_or_import_name.clone();
            }
        }

        for entry in &export_data.entries {
            if entry.kind == ast::ExportEntryKind::EmptyNamedExport {
                break;
            }

            let has_module_request = export_data.module_request.is_some();
            if !has_module_request {
                let matching_import = all_import_entries
                    .iter()
                    .find(|import| entry.local_or_import_name.as_ref() == Some(&import.local_name));
                if let Some(import_entry) = matching_import {
                    if import_entry.import_name.is_none() {
                        metadata.local_exports.push(export_record(entry, None));
                    } else {
                        metadata.indirect_exports.push(ModuleExportEntryRecord {
                            kind: entry.kind,
                            export_name: entry.export_name.clone(),
                            local_or_import_name: import_entry.import_name.clone(),
                            module_request: Some(import_entry.module_request.clone()),
                        });
                    }
                } else {
                    metadata.local_exports.push(export_record(entry, None));
                }
            } else if entry.kind == ast::ExportEntryKind::ModuleRequestAllButDefault {
                let module_request = export_data.module_request.as_ref().map(ModuleRequestRecord::from);
                metadata
                    .star_exports
                    .push(export_record(entry, module_request.as_ref()));
            } else {
                let module_request = export_data.module_request.as_ref().map(ModuleRequestRecord::from);
                metadata
                    .indirect_exports
                    .push(export_record(entry, module_request.as_ref()));
            }
        }
    }
}

fn export_record(entry: &ast::ExportEntry, module_request: Option<&ModuleRequestRecord>) -> ModuleExportEntryRecord {
    ModuleExportEntryRecord {
        kind: entry.kind,
        export_name: entry.export_name.clone(),
        local_or_import_name: entry.local_or_import_name.clone(),
        module_request: module_request.cloned(),
    }
}

fn requested_modules(scope: &ast::ScopeData) -> Vec<ModuleRequestRecord> {
    let mut modules = Vec::new();
    for child in &scope.children {
        match &child.inner {
            ast::StatementKind::Import(import_data) => {
                modules.push((
                    child.range.start.offset,
                    ModuleRequestRecord::from(&import_data.module_request),
                ));
            }
            ast::StatementKind::Export(export_data) => {
                if let Some(module_request) = &export_data.module_request {
                    modules.push((child.range.start.offset, ModuleRequestRecord::from(module_request)));
                }
            }
            _ => {}
        }
    }
    modules.sort_by_key(|(source_offset, _)| *source_offset);
    modules.into_iter().map(|(_, module_request)| module_request).collect()
}

fn collect_module_declaration(
    declaration: &ast::StatementKind,
    is_exported: bool,
    function_index: i32,
    arena: &ast::AstArena,
    metadata: &mut ModuleDeclarationMetadata,
) {
    let default_name: ast::Utf16String = utf16!("*default*").into();
    match declaration {
        ast::StatementKind::FunctionDeclaration(function) => {
            let Some(name) = function.name else {
                return;
            };
            let is_default = is_exported && arena.name_slice(name) == default_name.as_slice();
            let function_name = if is_default {
                utf16!("default").into()
            } else {
                arena.name_of(name).clone()
            };
            metadata.function_names.push(function_name);
            metadata.lexical_bindings.push(ModuleLexicalBindingRecord {
                name: arena.name_of(name).clone(),
                is_constant: false,
                function_index,
            });
        }
        ast::StatementKind::ClassDeclaration(class_data) => {
            if let Some(name) = class_data.name {
                metadata.lexical_bindings.push(ModuleLexicalBindingRecord {
                    name: arena.name_of(name).clone(),
                    is_constant: false,
                    function_index: -1,
                });
            }
        }
        ast::StatementKind::VariableDeclaration(declaration) if declaration.kind != ast::DeclarationKind::Var => {
            let is_constant = declaration.kind == ast::DeclarationKind::Const;
            for declarator in &declaration.declarations {
                for_each_bound_name(&declarator.target, arena, &mut |name| {
                    metadata.lexical_bindings.push(ModuleLexicalBindingRecord {
                        name: name.to_vec().into(),
                        is_constant,
                        function_index: -1,
                    });
                });
            }
        }
        ast::StatementKind::UsingDeclaration(declarations) => {
            for declarator in declarations.iter() {
                for_each_bound_name(&declarator.target, arena, &mut |name| {
                    metadata.lexical_bindings.push(ModuleLexicalBindingRecord {
                        name: name.to_vec().into(),
                        is_constant: false,
                        function_index: -1,
                    });
                });
            }
        }
        _ => {}
    }
}

fn collect_var_names_recursive(
    statement: &ast::StatementKind,
    arena: &ast::AstArena,
    names: &mut Vec<ast::Utf16String>,
) {
    match statement {
        ast::StatementKind::VariableDeclaration(declaration) if declaration.kind == ast::DeclarationKind::Var => {
            for declarator in &declaration.declarations {
                for_each_bound_name(&declarator.target, arena, &mut |name| names.push(name.to_vec().into()));
            }
        }
        _ => {
            for_each_child_statement(statement, arena, &mut |child| {
                collect_var_names_recursive(child, arena, names);
            });
        }
    }
}

fn collect_module_var_names(statement: &ast::StatementKind, arena: &ast::AstArena, names: &mut Vec<ast::Utf16String>) {
    match statement {
        ast::StatementKind::VariableDeclaration(declaration) if declaration.kind == ast::DeclarationKind::Var => {
            for declarator in &declaration.declarations {
                for_each_bound_name(&declarator.target, arena, &mut |name| names.push(name.to_vec().into()));
            }
        }
        ast::StatementKind::Export(export_data) => {
            if let Some(ref statement) = export_data.statement {
                collect_module_var_names(&statement.inner, arena, names);
            }
        }
        _ => {
            for_each_child_statement(statement, arena, &mut |child| {
                collect_module_var_names(child, arena, names);
            });
        }
    }
}

fn for_each_bound_name(
    target: &ast::VariableDeclaratorTarget,
    arena: &ast::AstArena,
    callback: &mut dyn FnMut(&[u16]),
) {
    match target {
        ast::VariableDeclaratorTarget::Identifier(identifier) => callback(arena.name_slice(*identifier)),
        ast::VariableDeclaratorTarget::BindingPattern(pattern) => {
            for_each_bound_name_in_pattern(pattern, arena, callback);
        }
    }
}

fn for_each_bound_name_in_pattern(
    pattern: &ast::BindingPattern,
    arena: &ast::AstArena,
    callback: &mut dyn FnMut(&[u16]),
) {
    for entry in &pattern.entries {
        match &entry.alias {
            Some(ast::BindingEntryAlias::Identifier(identifier)) => callback(arena.name_slice(*identifier)),
            Some(ast::BindingEntryAlias::BindingPattern(pattern)) => {
                for_each_bound_name_in_pattern(pattern, arena, callback);
            }
            Some(ast::BindingEntryAlias::MemberExpression(_)) => {}
            None => {
                if let Some(ast::BindingEntryName::Identifier(identifier)) = &entry.name {
                    callback(arena.name_slice(*identifier));
                }
            }
        }
    }
}

fn for_each_child_statement(
    statement: &ast::StatementKind,
    arena: &ast::AstArena,
    callback: &mut dyn FnMut(&ast::StatementKind),
) {
    match statement {
        ast::StatementKind::Block(scope) => {
            for child in &arena.scopes[*scope].children {
                callback(&child.inner);
            }
        }
        ast::StatementKind::If(data) => {
            callback(&data.consequent.inner);
            if let Some(alternate) = &data.alternate {
                callback(&alternate.inner);
            }
        }
        ast::StatementKind::While(data) | ast::StatementKind::DoWhile(data) => {
            callback(&data.body.inner);
        }
        ast::StatementKind::With(data) => callback(&data.body.inner),
        ast::StatementKind::For(data) => {
            if let Some(ast::ForInit::Declaration(declaration)) = &data.init {
                callback(&declaration.inner);
            }
            callback(&data.body.inner);
        }
        ast::StatementKind::ForInOf(data) => {
            if let ast::ForInOfLhs::Declaration(declaration) = &data.lhs {
                callback(&declaration.inner);
            }
            callback(&data.body.inner);
        }
        ast::StatementKind::Switch(data) => {
            for case in &data.cases {
                for child in &arena.scopes[case.scope].children {
                    callback(&child.inner);
                }
            }
        }
        ast::StatementKind::Labelled(data) => callback(&data.item.inner),
        ast::StatementKind::Try(data) => {
            callback(&data.block.inner);
            if let Some(catch) = &data.handler {
                callback(&catch.body.inner);
            }
            if let Some(finalizer) = &data.finalizer {
                callback(&finalizer.inner);
            }
        }
        ast::StatementKind::Export(export_data) => {
            if let Some(statement) = &export_data.statement {
                callback(&statement.inner);
            }
        }
        _ => {}
    }
}

struct ProgramRecord<'a> {
    kind: ProgramKind,
    executable: ExecutableRecord<'a>,
}

impl<'a> From<&'a CompiledProgram> for ProgramRecord<'a> {
    fn from(compiled: &'a CompiledProgram) -> Self {
        match &compiled.bytecode {
            CompiledProgramBytecode::Program(bytecode) => Self {
                kind: ProgramKind::ScriptOrModule,
                executable: ExecutableRecord {
                    generator: &bytecode.generator,
                    assembled: &bytecode.assembled,
                },
            },
            CompiledProgramBytecode::AsyncModule(bytecode) => Self {
                kind: ProgramKind::AsyncModule,
                executable: ExecutableRecord {
                    generator: &bytecode.generator,
                    assembled: &bytecode.assembled,
                },
            },
        }
    }
}

impl Encode for ProgramRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.kind.encode(encoder);
        self.executable.encode(encoder);
    }
}

impl ProgramRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedProgramRecord> {
        Some(DecodedProgramRecord {
            kind: ProgramKind::decode(decoder)?,
            executable: ExecutableRecord::decode(decoder)?,
        })
    }
}

struct DecodedProgramRecord {
    kind: ProgramKind,
    executable: DecodedExecutableRecord,
}

impl DecodedProgramRecord {
    fn validate(&self) {
        let _ = self.kind as u8;
        self.executable.validate();
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.executable.source_ranges_are_valid(source_len)
    }

    fn indices_are_valid(&self) -> bool {
        self.executable.indices_are_valid()
    }
}

#[repr(u8)]
#[derive(Clone, Copy)]
enum ProgramKind {
    ScriptOrModule = 0,
    AsyncModule = 1,
}

impl Encode for ProgramKind {
    fn encode(&self, encoder: &mut Encoder) {
        (*self as u8).encode(encoder);
    }
}

impl Decode for ProgramKind {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::ScriptOrModule),
            1 => Some(Self::AsyncModule),
            _ => None,
        }
    }
}

struct ExecutableRecord<'a> {
    generator: &'a Generator,
    assembled: &'a AssembledBytecode,
}

impl Encode for ExecutableRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.generator.strict.encode(encoder);
        self.assembled.number_of_registers.encode(encoder);
        self.assembled.number_of_arguments.encode(encoder);
        CacheCounters(self.generator).encode(encoder);
        self.generator.this_value_needs_environment_resolution.encode(encoder);
        self.generator.length_identifier.map(|index| index.0).encode(encoder);

        encoder.align_bytes_payload_to(BYTECODE_ALIGNMENT);
        Bytes(&self.assembled.bytecode).encode(encoder);
        Utf16Table(&self.generator.identifier_table).encode(encoder);
        Utf16Table(&self.generator.property_key_table).encode(encoder);
        Utf16Table(&self.generator.string_table).encode(encoder);
        ConstantTable(&self.generator.constants).encode(encoder);
        ExceptionHandlerTable(self.assembled).encode(encoder);
        SourceMapTable(self.assembled).encode(encoder);
        LocalVariableTable(self.generator).encode(encoder);
        SharedFunctionTable(self.generator).encode(encoder);
        ClassBlueprintTable(self.generator).encode(encoder);
    }
}

impl ExecutableRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedExecutableRecord> {
        Some(DecodedExecutableRecord {
            strict: bool::decode(decoder)?,
            number_of_registers: u32::decode(decoder)?,
            number_of_arguments: u32::decode(decoder)?,
            cache_counters: CacheCounters::decode(decoder)?,
            this_value_needs_environment_resolution: bool::decode(decoder)?,
            length_identifier: Option::<u32>::decode(decoder)?,
            bytecode: {
                decoder.align_bytes_payload_to(BYTECODE_ALIGNMENT)?;
                DecodedBytecodeBytes::decode(decoder)?
            },
            identifier_table: Utf16Table::decode(decoder)?,
            property_key_table: Utf16Table::decode(decoder)?,
            string_table: Utf16Table::decode(decoder)?,
            constants: ConstantTable::decode(decoder)?,
            exception_handlers: ExceptionHandlerTable::decode(decoder)?,
            source_map: SourceMapTable::decode(decoder)?,
            local_variables: LocalVariableTable::decode(decoder)?,
            shared_functions: SharedFunctionTable::decode(decoder)?,
            class_blueprints: ClassBlueprintTable::decode(decoder)?,
        })
    }
}

struct DecodedExecutableRecord {
    strict: bool,
    number_of_registers: u32,
    number_of_arguments: u32,
    cache_counters: DecodedCacheCounters,
    this_value_needs_environment_resolution: bool,
    length_identifier: Option<u32>,
    bytecode: DecodedBytecodeBytes,
    identifier_table: DecodedUtf16Table,
    property_key_table: DecodedUtf16Table,
    string_table: DecodedUtf16Table,
    constants: DecodedConstantTable,
    exception_handlers: DecodedExceptionHandlerTable,
    source_map: DecodedSourceMapTable,
    local_variables: DecodedLocalVariableTable,
    shared_functions: DecodedFunctionTable,
    class_blueprints: DecodedClassBlueprintTable,
}

impl DecodedExecutableRecord {
    fn validate(&self) {
        let _ = self.strict;
        let _ = self.number_of_registers + self.number_of_arguments;
        self.cache_counters.validate();
        let _ = self.this_value_needs_environment_resolution;
        let _ = self.length_identifier;
        let _ = self.bytecode.len()
            + self.identifier_table.len()
            + self.property_key_table.len()
            + self.string_table.len()
            + self.constants.len()
            + self.exception_handlers.len()
            + self.source_map.len()
            + self.local_variables.len()
            + self.shared_functions.len()
            + self.class_blueprints.len();
        self.shared_functions.validate();
        self.class_blueprints.validate();
    }

    fn validate_cached_bytecode(&self) -> Result<(), ValidationErrorKind> {
        let bounds = FFIValidatorBounds {
            number_of_registers: self.number_of_registers,
            number_of_locals: self.local_variables.len() as u32,
            number_of_constants: self.constants.len() as u32,
            number_of_arguments: self.number_of_arguments,
            identifier_table_size: self.identifier_table.len() as u32,
            string_table_size: self.string_table.len() as u32,
            property_key_table_size: self.property_key_table.len() as u32,
            regex_table_size: 0,
            property_lookup_cache_count: self.cache_counters.property_lookup_cache_count,
            global_variable_cache_count: self.cache_counters.global_variable_cache_count,
            template_object_cache_count: self.cache_counters.template_object_cache_count,
            object_shape_cache_count: self.cache_counters.object_shape_cache_count,
            object_property_iterator_cache_count: self.cache_counters.object_property_iterator_cache_count,
            class_blueprint_count: self.class_blueprints.len() as u32,
            shared_function_data_count: self.shared_functions.len() as u32,
            completion_type_variant_count: COMPLETION_TYPE_VARIANT_COUNT,
            iterator_hint_variant_count: ITERATOR_HINT_VARIANT_COUNT,
            environment_mode_variant_count: ENVIRONMENT_MODE_VARIANT_COUNT,
            put_kind_variant_count: PUT_KIND_VARIANT_COUNT,
            arguments_kind_variant_count: ARGUMENTS_KIND_VARIANT_COUNT,
        };

        let exception_handlers = self
            .exception_handlers
            .values()
            .ok_or(ValidationErrorKind::InvalidLength)?;
        let exception_handlers: Vec<FFIExceptionHandlerOffsets> = exception_handlers
            .iter()
            .map(|handler| FFIExceptionHandlerOffsets {
                start: handler.start_offset,
                end: handler.end_offset,
                handler: handler.handler_offset,
            })
            .collect();
        let source_map = self.source_map.values().ok_or(ValidationErrorKind::InvalidLength)?;
        let source_map_offsets: Vec<u32> = source_map.iter().map(|entry| entry.bytecode_offset).collect();

        validate_bytecode(
            self.bytecode.as_slice(),
            &bounds,
            &[],
            &exception_handlers,
            &source_map_offsets,
        )
        .map_err(|error| error.kind)?;

        self.shared_functions.validate_cached_bytecode()?;

        Ok(())
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.shared_functions.source_ranges_are_valid(source_len)
            && self.class_blueprints.source_ranges_are_valid(source_len)
    }

    fn indices_are_valid(&self) -> bool {
        self.length_identifier
            .is_none_or(|index| (index as usize) < self.property_key_table.len())
            && self.class_blueprints.indices_are_valid(self.shared_functions.len())
    }
}

struct DecodedCachedExecutableRecord {
    bytes: DecodedBytecodeBytes,
}

impl DecodedCachedExecutableRecord {
    fn decode_executable(&self) -> Option<DecodedExecutableRecord> {
        let mut decoder = self.bytes.decoder();
        let executable = ExecutableRecord::decode(&mut decoder)?;
        decoder.is_empty().then_some(executable)
    }

    fn validate_cached_bytecode(&self) -> Result<(), ValidationErrorKind> {
        self.decode_executable()
            .ok_or(ValidationErrorKind::InvalidLength)?
            .validate_cached_bytecode()
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.decode_executable()
            .is_some_and(|executable| executable.source_ranges_are_valid(source_len))
    }

    fn validate(&self) {
        let _ = self.bytes.len();
    }
}

struct CacheCounters<'a>(&'a Generator);

impl Encode for CacheCounters<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.0.next_property_lookup_cache.encode(encoder);
        self.0.next_global_variable_cache.encode(encoder);
        self.0.next_template_object_cache.encode(encoder);
        self.0.next_object_shape_cache.encode(encoder);
        self.0.next_object_property_iterator_cache.encode(encoder);
    }
}

impl CacheCounters<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedCacheCounters> {
        Some(DecodedCacheCounters {
            property_lookup_cache_count: u32::decode(decoder)?,
            global_variable_cache_count: u32::decode(decoder)?,
            template_object_cache_count: u32::decode(decoder)?,
            object_shape_cache_count: u32::decode(decoder)?,
            object_property_iterator_cache_count: u32::decode(decoder)?,
        })
    }
}

struct DecodedCacheCounters {
    property_lookup_cache_count: u32,
    global_variable_cache_count: u32,
    template_object_cache_count: u32,
    object_shape_cache_count: u32,
    object_property_iterator_cache_count: u32,
}

impl DecodedCacheCounters {
    fn validate(&self) {
        let _ = self.property_lookup_cache_count
            + self.global_variable_cache_count
            + self.template_object_cache_count
            + self.object_shape_cache_count
            + self.object_property_iterator_cache_count;
    }
}

struct Utf16Table<'a>(&'a [ast::Utf16String]);

impl Encode for Utf16Table<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode(encoder, self.0, |value, encoder| Utf16(value).encode(encoder));
    }
}

impl Utf16Table<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedUtf16Table> {
        Some(DecodedUtf16Table {
            sequence: DecodedRecordSequence::decode(decoder)?,
        })
    }
}

struct DecodedUtf16Table {
    sequence: DecodedRecordSequence,
}

impl DecodedUtf16Table {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn into_values(self) -> Option<Vec<DecodedUtf16String>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(DecodedUtf16String::decode(&mut decoder)?);
        }
        decoder.is_empty().then_some(values)
    }
}

struct ConstantTable<'a>(&'a [ConstantValue]);

impl Encode for ConstantTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        u32_from_usize(self.0.len()).encode(encoder);

        let mut constant_encoder = Encoder::new();
        for constant in self.0 {
            constant.encode(&mut constant_encoder);
        }
        Bytes(&constant_encoder.finish()).encode(encoder);
    }
}

impl ConstantTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedConstantTable> {
        let count: usize = u32::decode(decoder)?.try_into().ok()?;
        let byte_length: usize = u32::decode(decoder)?.try_into().ok()?;
        // Constants are encoded as at least their one-byte tag.
        if count > byte_length {
            return None;
        }
        Some(DecodedConstantTable {
            count,
            bytes: decoder.bytecode_bytes(byte_length)?,
        })
    }
}

struct DecodedConstantTable {
    count: usize,
    bytes: DecodedBytecodeBytes,
}

impl DecodedConstantTable {
    fn len(&self) -> usize {
        self.count
    }

    fn into_constant_values(self) -> Option<Vec<ConstantValue>> {
        let mut decoder = Decoder::new(self.bytes.as_slice(), None);
        let mut constants = Vec::with_capacity(self.count);
        for _ in 0..self.count {
            constants.push(DecodedConstantValue::decode(&mut decoder)?.into_constant_value());
        }
        decoder.is_empty().then_some(constants)
    }
}

impl Encode for ConstantValue {
    fn encode(&self, encoder: &mut Encoder) {
        match self {
            ConstantValue::Number(value) => {
                (ConstantTag::Number as u8).encode(encoder);
                value.encode(encoder);
            }
            ConstantValue::Boolean(true) => (ConstantTag::BooleanTrue as u8).encode(encoder),
            ConstantValue::Boolean(false) => (ConstantTag::BooleanFalse as u8).encode(encoder),
            ConstantValue::Null => (ConstantTag::Null as u8).encode(encoder),
            ConstantValue::Undefined => (ConstantTag::Undefined as u8).encode(encoder),
            ConstantValue::Empty => (ConstantTag::Empty as u8).encode(encoder),
            ConstantValue::String(value) => {
                (ConstantTag::String as u8).encode(encoder);
                Utf16(value).encode(encoder);
            }
            ConstantValue::BigInt(value) => {
                (ConstantTag::BigInt as u8).encode(encoder);
                Bytes(value.as_bytes()).encode(encoder);
            }
            ConstantValue::WellKnownSymbol(symbol) => {
                (ConstantTag::WellKnownSymbol as u8).encode(encoder);
                (*symbol as u8).encode(encoder);
            }
            ConstantValue::AbstractOperation(operation) => {
                (ConstantTag::AbstractOperation as u8).encode(encoder);
                (*operation as u8).encode(encoder);
            }
        }
    }
}

impl Decode for ConstantValue {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            tag if tag == ConstantTag::Number as u8 => Some(Self::Number(f64::decode(decoder)?)),
            tag if tag == ConstantTag::BooleanTrue as u8 => Some(Self::Boolean(true)),
            tag if tag == ConstantTag::BooleanFalse as u8 => Some(Self::Boolean(false)),
            tag if tag == ConstantTag::Null as u8 => Some(Self::Null),
            tag if tag == ConstantTag::Undefined as u8 => Some(Self::Undefined),
            tag if tag == ConstantTag::Empty as u8 => Some(Self::Empty),
            tag if tag == ConstantTag::String as u8 => Some(Self::String(ast::Utf16String::decode(decoder)?)),
            tag if tag == ConstantTag::BigInt as u8 => {
                Some(Self::BigInt(String::from_utf8(ByteVector::decode(decoder)?).ok()?))
            }
            tag if tag == ConstantTag::WellKnownSymbol as u8 => match u8::decode(decoder)? {
                0 => Some(Self::WellKnownSymbol(WellKnownSymbolKind::SymbolIterator)),
                1 => Some(Self::WellKnownSymbol(WellKnownSymbolKind::SymbolAsyncIterator)),
                _ => None,
            },
            tag if tag == ConstantTag::AbstractOperation as u8 => match u8::decode(decoder)? {
                0 => Some(Self::AbstractOperation(AbstractOperationKind::AsyncIteratorClose)),
                1 => Some(Self::AbstractOperation(AbstractOperationKind::GetMethod)),
                2 => Some(Self::AbstractOperation(AbstractOperationKind::GetIteratorDirect)),
                3 => Some(Self::AbstractOperation(AbstractOperationKind::GetIteratorFromMethod)),
                4 => Some(Self::AbstractOperation(AbstractOperationKind::IteratorComplete)),
                _ => None,
            },
            _ => None,
        }
    }
}

enum DecodedConstantValue {
    Number(f64),
    Boolean(bool),
    Null,
    Undefined,
    Empty,
    String(DecodedUtf16String),
    BigInt(String),
    WellKnownSymbol(WellKnownSymbolKind),
    AbstractOperation(AbstractOperationKind),
}

impl DecodedConstantValue {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            tag if tag == ConstantTag::Number as u8 => Some(Self::Number(f64::decode(decoder)?)),
            tag if tag == ConstantTag::BooleanTrue as u8 => Some(Self::Boolean(true)),
            tag if tag == ConstantTag::BooleanFalse as u8 => Some(Self::Boolean(false)),
            tag if tag == ConstantTag::Null as u8 => Some(Self::Null),
            tag if tag == ConstantTag::Undefined as u8 => Some(Self::Undefined),
            tag if tag == ConstantTag::Empty as u8 => Some(Self::Empty),
            tag if tag == ConstantTag::String as u8 => Some(Self::String(DecodedUtf16String::decode(decoder)?)),
            tag if tag == ConstantTag::BigInt as u8 => {
                Some(Self::BigInt(String::from_utf8(ByteVector::decode(decoder)?).ok()?))
            }
            tag if tag == ConstantTag::WellKnownSymbol as u8 => match u8::decode(decoder)? {
                0 => Some(Self::WellKnownSymbol(WellKnownSymbolKind::SymbolIterator)),
                1 => Some(Self::WellKnownSymbol(WellKnownSymbolKind::SymbolAsyncIterator)),
                _ => None,
            },
            tag if tag == ConstantTag::AbstractOperation as u8 => match u8::decode(decoder)? {
                0 => Some(Self::AbstractOperation(AbstractOperationKind::AsyncIteratorClose)),
                1 => Some(Self::AbstractOperation(AbstractOperationKind::GetMethod)),
                2 => Some(Self::AbstractOperation(AbstractOperationKind::GetIteratorDirect)),
                3 => Some(Self::AbstractOperation(AbstractOperationKind::GetIteratorFromMethod)),
                4 => Some(Self::AbstractOperation(AbstractOperationKind::IteratorComplete)),
                _ => None,
            },
            _ => None,
        }
    }

    fn into_constant_value(self) -> ConstantValue {
        match self {
            Self::Number(value) => ConstantValue::Number(value),
            Self::Boolean(value) => ConstantValue::Boolean(value),
            Self::Null => ConstantValue::Null,
            Self::Undefined => ConstantValue::Undefined,
            Self::Empty => ConstantValue::Empty,
            Self::String(value) => ConstantValue::String(value.to_utf16_string()),
            Self::BigInt(value) => ConstantValue::BigInt(value),
            Self::WellKnownSymbol(value) => ConstantValue::WellKnownSymbol(value),
            Self::AbstractOperation(value) => ConstantValue::AbstractOperation(value),
        }
    }
}

struct ExceptionHandlerTable<'a>(&'a AssembledBytecode);

impl Encode for ExceptionHandlerTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode(encoder, &self.0.exception_handlers, |handler, encoder| {
            handler.start_offset.encode(encoder);
            handler.end_offset.encode(encoder);
            handler.handler_offset.encode(encoder);
        });
    }
}

impl ExceptionHandlerTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedExceptionHandlerTable> {
        Some(DecodedExceptionHandlerTable {
            sequence: DecodedRecordSequence::decode(decoder)?,
        })
    }
}

struct DecodedExceptionHandlerTable {
    sequence: DecodedRecordSequence,
}

impl DecodedExceptionHandlerTable {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn values(&self) -> Option<Vec<ExceptionHandler>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(ExceptionHandler {
                start_offset: u32::decode(&mut decoder)?,
                end_offset: u32::decode(&mut decoder)?,
                handler_offset: u32::decode(&mut decoder)?,
            });
        }
        decoder.is_empty().then_some(values)
    }

    fn into_values(self) -> Option<Vec<ExceptionHandler>> {
        self.values()
    }
}

struct SourceMapTable<'a>(&'a AssembledBytecode);

impl Encode for SourceMapTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode(encoder, &self.0.source_map, |entry, encoder| {
            entry.bytecode_offset.encode(encoder);
            entry.line.encode(encoder);
            entry.column.encode(encoder);
        });
    }
}

impl SourceMapTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedSourceMapTable> {
        Some(DecodedSourceMapTable {
            sequence: DecodedRecordSequence::decode(decoder)?,
        })
    }
}

struct DecodedSourceMapTable {
    sequence: DecodedRecordSequence,
}

impl DecodedSourceMapTable {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn values(&self) -> Option<Vec<SourceMapEntry>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(SourceMapEntry {
                bytecode_offset: u32::decode(&mut decoder)?,
                line: u32::decode(&mut decoder)?,
                column: u32::decode(&mut decoder)?,
            });
        }
        decoder.is_empty().then_some(values)
    }

    fn into_values(self) -> Option<Vec<SourceMapEntry>> {
        self.values()
    }
}

struct LocalVariableTable<'a>(&'a Generator);

impl Encode for LocalVariableTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode(encoder, &self.0.local_variables, |local_variable, encoder| {
            Utf16(&local_variable.name).encode(encoder);
            local_variable.is_lexically_declared.encode(encoder);
            local_variable
                .is_initialized_during_declaration_instantiation
                .encode(encoder);
        });
    }
}

impl LocalVariableTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedLocalVariableTable> {
        Some(DecodedLocalVariableTable {
            sequence: DecodedRecordSequence::decode(decoder)?,
        })
    }
}

struct DecodedLocalVariableTable {
    sequence: DecodedRecordSequence,
}

impl DecodedLocalVariableTable {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn into_values(self) -> Option<Vec<DecodedLocalVariable>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(DecodedLocalVariable {
                name: DecodedUtf16String::decode(&mut decoder)?,
                is_lexically_declared: bool::decode(&mut decoder)?,
                is_initialized_during_declaration_instantiation: bool::decode(&mut decoder)?,
            });
        }
        decoder.is_empty().then_some(values)
    }
}

struct DecodedLocalVariable {
    name: DecodedUtf16String,
    is_lexically_declared: bool,
    is_initialized_during_declaration_instantiation: bool,
}

impl DecodedLocalVariable {
    fn into_local_variable(self) -> LocalVariable {
        LocalVariable {
            name: self.name.to_utf16_string(),
            is_lexically_declared: self.is_lexically_declared,
            is_initialized_during_declaration_instantiation: self.is_initialized_during_declaration_instantiation,
        }
    }
}

struct SharedFunctionTable<'a>(&'a Generator);

impl Encode for SharedFunctionTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode_with_alignment(
            encoder,
            &self.0.shared_function_data,
            BYTECODE_ALIGNMENT,
            |shared_data, encoder| {
                FunctionRecord {
                    shared_data,
                    arena: &self.0.arena,
                }
                .encode(encoder);
            },
        );
    }
}

impl SharedFunctionTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedFunctionTable> {
        Some(DecodedFunctionTable {
            sequence: DecodedRecordSequence::decode_with_alignment(decoder, BYTECODE_ALIGNMENT)?,
        })
    }
}

struct DecodedFunctionTable {
    sequence: DecodedRecordSequence,
}

impl DecodedFunctionTable {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn validate(&self) {
        let _ = self.sequence.len();
    }

    fn into_values(self) -> Option<Vec<DecodedFunctionRecord>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(FunctionRecord::decode(&mut decoder)?);
        }
        decoder.is_empty().then_some(values)
    }

    fn for_each(&self, mut callback: impl FnMut(DecodedFunctionRecord) -> Option<()>) -> Option<()> {
        let mut decoder = self.sequence.decoder();
        for _ in 0..self.sequence.len() {
            callback(FunctionRecord::decode(&mut decoder)?)?;
        }
        decoder.is_empty().then_some(())
    }

    fn validate_cached_bytecode(&self) -> Result<(), ValidationErrorKind> {
        let mut decoder = self.sequence.decoder();
        for _ in 0..self.sequence.len() {
            let function = FunctionRecord::decode(&mut decoder).ok_or(ValidationErrorKind::InvalidLength)?;
            function.precompiled.validate_cached_bytecode()?;
        }
        decoder
            .is_empty()
            .then_some(())
            .ok_or(ValidationErrorKind::InvalidLength)
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.for_each(|function| function.source_ranges_are_valid(source_len).then_some(()))
            .is_some()
    }
}

struct DeclarationFunctionTable<'a>(&'a [PendingSharedFunctionData]);

impl Encode for DeclarationFunctionTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        u32_from_usize(self.0.len()).encode(encoder);
        let mut payload_encoder = Encoder::new();
        for shared_data in self.0 {
            let arena = shared_data
                .arena
                .as_deref()
                .expect("bytecode cache declaration function is missing its AST arena");
            FunctionRecord { shared_data, arena }.encode(&mut payload_encoder);
        }
        encoder.align_bytes_payload_to(BYTECODE_ALIGNMENT);
        Bytes(&payload_encoder.finish()).encode(encoder);
    }
}

impl DeclarationFunctionTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Vec<DecodedFunctionRecord>> {
        let count: usize = u32::decode(decoder)?.try_into().ok()?;
        decoder.align_bytes_payload_to(BYTECODE_ALIGNMENT)?;
        let byte_length: usize = u32::decode(decoder)?.try_into().ok()?;
        if count > byte_length {
            return None;
        }
        let bytes = decoder.bytecode_bytes(byte_length)?;
        let mut decoder = bytes.decoder();
        let mut values = Vec::with_capacity(count);
        for _ in 0..count {
            values.push(FunctionRecord::decode(&mut decoder)?);
        }
        decoder.is_empty().then_some(values)
    }
}

struct FunctionRecord<'a> {
    shared_data: &'a PendingSharedFunctionData,
    arena: &'a ast::AstArena,
}

impl Encode for FunctionRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        let function_data = self
            .shared_data
            .function_data
            .as_ref()
            .expect("bytecode cache requires function data to be retained until serialization");
        let precompiled = self
            .shared_data
            .precompiled_function
            .as_ref()
            .expect("fully compiled bytecode cache entry is missing nested function bytecode");

        self.function_name(function_data).encode(encoder);
        function_data.source_text_start.encode(encoder);
        function_data.source_text_end.encode(encoder);
        function_data.function_length.encode(encoder);
        u32_from_usize(function_data.parameters.len()).encode(encoder);
        (function_data.kind as u8).encode(encoder);
        function_data.is_strict_mode.encode(encoder);
        function_data.is_arrow_function.encode(encoder);
        SimpleParameterList {
            function_data,
            arena: self.function_arena(),
        }
        .encode(encoder);
        function_data.parsing_insights.uses_this.encode(encoder);
        function_data
            .parsing_insights
            .uses_this_from_environment
            .encode(encoder);
        ClassFieldInitializerName(self.shared_data).encode(encoder);
        precompiled.metadata.encode(encoder);
        PrecompiledFunctionRecord(precompiled).encode(encoder);
    }
}

impl FunctionRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedFunctionRecord> {
        Some(DecodedFunctionRecord {
            name: Option::<DecodedUtf16String>::decode(decoder)?,
            source_text_start: u32::decode(decoder)?,
            source_text_end: u32::decode(decoder)?,
            function_length: i32::decode(decoder)?,
            formal_parameter_count: u32::decode(decoder)?,
            kind: ast::FunctionKind::decode(decoder)?,
            is_strict_mode: bool::decode(decoder)?,
            is_arrow_function: bool::decode(decoder)?,
            parameter_names: SimpleParameterList::decode(decoder)?,
            uses_this: bool::decode(decoder)?,
            uses_this_from_environment: bool::decode(decoder)?,
            class_field_initializer_name: ClassFieldInitializerName::decode(decoder)?,
            metadata: FunctionSfdMetadata::decode(decoder)?,
            precompiled: PrecompiledFunctionRecord::decode(decoder)?,
        })
    }
}

struct DecodedFunctionRecord {
    name: Option<DecodedUtf16String>,
    source_text_start: u32,
    source_text_end: u32,
    function_length: i32,
    formal_parameter_count: u32,
    kind: ast::FunctionKind,
    is_strict_mode: bool,
    is_arrow_function: bool,
    parameter_names: Option<Vec<DecodedUtf16String>>,
    uses_this: bool,
    uses_this_from_environment: bool,
    class_field_initializer_name: Option<(DecodedUtf16String, bool)>,
    metadata: FunctionSfdMetadata,
    precompiled: DecodedCachedExecutableRecord,
}

impl DecodedFunctionRecord {
    fn validate(&self) {
        let _ = self.name.as_ref().map(DecodedUtf16String::len);
        let _ = self.source_text_start;
        let _ = self.source_text_end;
        let _ = self.formal_parameter_count;
        let _ = self.function_length;
        let _ = self.kind as u8;
        let _ = self.is_strict_mode || self.is_arrow_function || self.uses_this || self.uses_this_from_environment;
        let _ = self.parameter_names.as_ref().map(|names| names.len());
        let _ = self.class_field_initializer_name.as_ref().map(|(name, _)| name.len());
        self.precompiled.validate();
        validate_function_metadata(&self.metadata);
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        source_span_is_valid(self.source_text_start, self.source_text_end, source_len)
            && self.precompiled.source_ranges_are_valid(source_len)
    }
}

impl<'a> FunctionRecord<'a> {
    fn function_name(&self, function_data: &'a ast::FunctionData) -> Option<Utf16<'a>> {
        self.shared_data
            .name_override
            .as_deref()
            .or_else(|| function_data.name.map(|name| self.function_arena().name_slice(name)))
            .map(Utf16)
    }

    fn function_arena(&self) -> &'a ast::AstArena {
        self.shared_data.arena.as_deref().unwrap_or(self.arena)
    }
}

struct SimpleParameterList<'a> {
    function_data: &'a ast::FunctionData,
    arena: &'a ast::AstArena,
}

impl Encode for SimpleParameterList<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        let names = simple_parameter_names(self.function_data, self.arena);
        names.is_some().encode(encoder);
        if let Some(names) = names {
            encoder.sequence(&names, |name, encoder| Utf16(name).encode(encoder));
        }
    }
}

impl SimpleParameterList<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Option<Vec<DecodedUtf16String>>> {
        if bool::decode(decoder)? {
            Some(Some(decoder.sequence_values(DecodedUtf16String::decode)?))
        } else {
            Some(None)
        }
    }
}

fn simple_parameter_names<'a>(
    function_data: &'a ast::FunctionData,
    arena: &'a ast::AstArena,
) -> Option<Vec<&'a [u16]>> {
    let mut names = Vec::with_capacity(function_data.parameters.len());
    for parameter in &function_data.parameters {
        if parameter.is_rest || parameter.default_value.is_some() {
            return None;
        }
        let ast::FunctionParameterBinding::Identifier(identifier) = &parameter.binding else {
            return None;
        };
        names.push(arena.name_slice(*identifier));
    }
    Some(names)
}

struct ClassFieldInitializerName<'a>(&'a PendingSharedFunctionData);

impl Encode for ClassFieldInitializerName<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.0
            .class_field_initializer_name
            .as_ref()
            .map(|(name, is_private)| (Utf16(name.as_slice()), *is_private))
            .encode(encoder);
    }
}

impl ClassFieldInitializerName<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Option<(DecodedUtf16String, bool)>> {
        Option::<(DecodedUtf16String, bool)>::decode(decoder)
    }
}

impl Encode for (Utf16<'_>, bool) {
    fn encode(&self, encoder: &mut Encoder) {
        self.0.encode(encoder);
        self.1.encode(encoder);
    }
}

impl Decode for (DecodedUtf16String, bool) {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some((DecodedUtf16String::decode(decoder)?, bool::decode(decoder)?))
    }
}

impl Encode for FunctionSfdMetadata {
    fn encode(&self, encoder: &mut Encoder) {
        self.uses_this.encode(encoder);
        self.this_value_needs_environment_resolution.encode(encoder);
        self.function_environment_needed.encode(encoder);
        self.function_environment_bindings_count.encode(encoder);
        self.var_environment_bindings_count.encode(encoder);
        self.might_need_arguments.encode(encoder);
        self.contains_eval.encode(encoder);
    }
}

impl FunctionSfdMetadata {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        Some(Self {
            uses_this: bool::decode(decoder)?,
            this_value_needs_environment_resolution: bool::decode(decoder)?,
            function_environment_needed: bool::decode(decoder)?,
            function_environment_bindings_count: usize::decode(decoder)?,
            var_environment_bindings_count: usize::decode(decoder)?,
            might_need_arguments: bool::decode(decoder)?,
            contains_eval: bool::decode(decoder)?,
        })
    }
}

fn validate_function_metadata(metadata: &FunctionSfdMetadata) {
    let _ = metadata.uses_this
        || metadata.this_value_needs_environment_resolution
        || metadata.function_environment_needed
        || metadata.might_need_arguments
        || metadata.contains_eval;
    let _ = metadata.function_environment_bindings_count + metadata.var_environment_bindings_count;
}

struct PrecompiledFunctionRecord<'a>(&'a PrecompiledFunction);

impl Encode for PrecompiledFunctionRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        let mut payload_encoder = Encoder::new();
        ExecutableRecord {
            generator: &self.0.generator,
            assembled: &self.0.assembled,
        }
        .encode(&mut payload_encoder);
        encoder.align_bytes_payload_to(BYTECODE_ALIGNMENT);
        Bytes(&payload_encoder.finish()).encode(encoder);
    }
}

impl PrecompiledFunctionRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedCachedExecutableRecord> {
        decoder.align_bytes_payload_to(BYTECODE_ALIGNMENT)?;
        Some(DecodedCachedExecutableRecord {
            bytes: DecodedBytecodeBytes::decode(decoder)?,
        })
    }
}

struct ClassBlueprintTable<'a>(&'a Generator);

impl Encode for ClassBlueprintTable<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        DecodedRecordSequence::encode(encoder, &self.0.class_blueprints, |blueprint, encoder| {
            ClassBlueprintRecord(blueprint).encode(encoder);
        });
    }
}

impl ClassBlueprintTable<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedClassBlueprintTable> {
        Some(DecodedClassBlueprintTable {
            sequence: DecodedRecordSequence::decode(decoder)?,
        })
    }
}

struct DecodedClassBlueprintTable {
    sequence: DecodedRecordSequence,
}

impl DecodedClassBlueprintTable {
    fn len(&self) -> usize {
        self.sequence.len()
    }

    fn validate(&self) {
        let _ = self.sequence.len();
    }

    fn into_values(self) -> Option<Vec<DecodedClassBlueprintRecord>> {
        let mut decoder = self.sequence.decoder();
        let mut values = Vec::with_capacity(self.sequence.len());
        for _ in 0..self.sequence.len() {
            values.push(ClassBlueprintRecord::decode(&mut decoder)?);
        }
        decoder.is_empty().then_some(values)
    }

    fn for_each(&self, mut callback: impl FnMut(DecodedClassBlueprintRecord) -> Option<()>) -> Option<()> {
        let mut decoder = self.sequence.decoder();
        for _ in 0..self.sequence.len() {
            callback(ClassBlueprintRecord::decode(&mut decoder)?)?;
        }
        decoder.is_empty().then_some(())
    }

    fn source_ranges_are_valid(&self, source_len: usize) -> bool {
        self.for_each(|blueprint| blueprint.source_range_is_valid(source_len).then_some(()))
            .is_some()
    }

    fn indices_are_valid(&self, shared_function_count: usize) -> bool {
        self.for_each(|blueprint| blueprint.indices_are_valid(shared_function_count).then_some(()))
            .is_some()
    }
}

struct ClassBlueprintRecord<'a>(&'a PendingClassBlueprint);

impl Encode for ClassBlueprintRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.0.name.as_deref().map(Utf16).encode(encoder);
        self.0.source_text_offset.encode(encoder);
        self.0.source_text_length.encode(encoder);
        self.0.constructor_sfd_index.encode(encoder);
        self.0.has_super_class.encode(encoder);
        self.0.has_name.encode(encoder);
        encoder.sequence(&self.0.elements, |element, encoder| {
            ClassElementRecord(element).encode(encoder);
        });
    }
}

impl ClassBlueprintRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedClassBlueprintRecord> {
        Some(DecodedClassBlueprintRecord {
            name: Option::<DecodedUtf16String>::decode(decoder)?,
            source_text_offset: usize::decode(decoder)?,
            source_text_length: usize::decode(decoder)?,
            constructor_sfd_index: u32::decode(decoder)?,
            has_super_class: bool::decode(decoder)?,
            has_name: bool::decode(decoder)?,
            elements: decoder.sequence_values(ClassElementRecord::decode)?,
        })
    }
}

struct DecodedClassBlueprintRecord {
    name: Option<DecodedUtf16String>,
    source_text_offset: usize,
    source_text_length: usize,
    constructor_sfd_index: u32,
    has_super_class: bool,
    has_name: bool,
    elements: Vec<DecodedClassElementRecord>,
}

impl DecodedClassBlueprintRecord {
    fn source_range_is_valid(&self, source_len: usize) -> bool {
        source_range_is_valid(self.source_text_offset, self.source_text_length, source_len)
    }

    fn indices_are_valid(&self, shared_function_count: usize) -> bool {
        (self.constructor_sfd_index as usize) < shared_function_count
            && self
                .elements
                .iter()
                .all(|element| element.indices_are_valid(shared_function_count))
    }
}

impl From<DecodedClassBlueprintRecord> for PendingClassBlueprint {
    fn from(record: DecodedClassBlueprintRecord) -> Self {
        Self {
            name: record.name.map(|name| name.to_utf16_string()),
            source_text_offset: record.source_text_offset,
            source_text_length: record.source_text_length,
            constructor_sfd_index: record.constructor_sfd_index,
            has_super_class: record.has_super_class,
            has_name: record.has_name,
            elements: record.elements.into_iter().map(PendingClassElement::from).collect(),
        }
    }
}

struct ClassElementRecord<'a>(&'a PendingClassElement);

impl Encode for ClassElementRecord<'_> {
    fn encode(&self, encoder: &mut Encoder) {
        self.0.kind.encode(encoder);
        self.0.is_static.encode(encoder);
        self.0.is_private.encode(encoder);
        self.0.private_identifier.as_deref().map(Utf16).encode(encoder);
        self.0.shared_function_data_index.encode(encoder);
        self.0.has_initializer.encode(encoder);
        literal_value_kind_tag(self.0.literal_value_kind).encode(encoder);
        self.0.literal_value_number.encode(encoder);
        self.0.literal_value_string.as_deref().map(Utf16).encode(encoder);
    }
}

impl ClassElementRecord<'_> {
    fn decode(decoder: &mut Decoder<'_>) -> Option<DecodedClassElementRecord> {
        Some(DecodedClassElementRecord {
            kind: u8::decode(decoder)?,
            is_static: bool::decode(decoder)?,
            is_private: bool::decode(decoder)?,
            private_identifier: Option::<DecodedUtf16String>::decode(decoder)?,
            shared_function_data_index: Option::<u32>::decode(decoder)?,
            has_initializer: bool::decode(decoder)?,
            literal_value_kind: PendingLiteralValueKind::decode(decoder)?,
            literal_value_number: f64::decode(decoder)?,
            literal_value_string: Option::<DecodedUtf16String>::decode(decoder)?,
        })
    }
}

struct DecodedClassElementRecord {
    kind: u8,
    is_static: bool,
    is_private: bool,
    private_identifier: Option<DecodedUtf16String>,
    shared_function_data_index: Option<u32>,
    has_initializer: bool,
    literal_value_kind: PendingLiteralValueKind,
    literal_value_number: f64,
    literal_value_string: Option<DecodedUtf16String>,
}

impl DecodedClassElementRecord {
    fn indices_are_valid(&self, shared_function_count: usize) -> bool {
        let shared_function_data_index_is_valid = || {
            self.shared_function_data_index
                .is_some_and(|index| (index as usize) < shared_function_count)
        };

        match self.kind {
            0 | 1 | 2 | 4 => shared_function_data_index_is_valid(),
            3 => {
                if self.has_initializer && matches!(self.literal_value_kind, PendingLiteralValueKind::None) {
                    shared_function_data_index_is_valid()
                } else {
                    self.shared_function_data_index
                        .is_none_or(|index| (index as usize) < shared_function_count)
                }
            }
            _ => false,
        }
    }
}

impl From<DecodedClassElementRecord> for PendingClassElement {
    fn from(record: DecodedClassElementRecord) -> Self {
        Self {
            kind: record.kind,
            is_static: record.is_static,
            is_private: record.is_private,
            private_identifier: record.private_identifier.map(|identifier| identifier.to_utf16_string()),
            shared_function_data_index: record.shared_function_data_index,
            has_initializer: record.has_initializer,
            literal_value_kind: record.literal_value_kind,
            literal_value_number: record.literal_value_number,
            literal_value_string: record.literal_value_string.map(|value| value.to_utf16_string()),
        }
    }
}

impl Decode for PendingLiteralValueKind {
    fn decode(decoder: &mut Decoder<'_>) -> Option<Self> {
        match u8::decode(decoder)? {
            0 => Some(Self::None),
            1 => Some(Self::Number),
            2 => Some(Self::BooleanTrue),
            3 => Some(Self::BooleanFalse),
            4 => Some(Self::Null),
            5 => Some(Self::String),
            _ => None,
        }
    }
}

fn literal_value_kind_tag(kind: PendingLiteralValueKind) -> u8 {
    match kind {
        PendingLiteralValueKind::None => 0,
        PendingLiteralValueKind::Number => 1,
        PendingLiteralValueKind::BooleanTrue => 2,
        PendingLiteralValueKind::BooleanFalse => 3,
        PendingLiteralValueKind::Null => 4,
        PendingLiteralValueKind::String => 5,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn empty_record_sequence(encoder: &mut Encoder) {
        DecodedRecordSequence::encode::<u8>(encoder, &[], |_, _| {});
    }

    fn cached_executable_with_shared_function(function_payload: Option<Vec<u8>>) -> DecodedCachedExecutableRecord {
        let mut encoder = Encoder::new();

        false.encode(&mut encoder); // Strict.
        0u32.encode(&mut encoder); // Number of registers.
        0u32.encode(&mut encoder); // Number of arguments.
        for _ in 0..5 {
            0u32.encode(&mut encoder);
        }
        false.encode(&mut encoder); // This value needs environment resolution.
        Option::<u32>::None.encode(&mut encoder);

        Bytes(&[]).encode(&mut encoder); // Bytecode.
        empty_record_sequence(&mut encoder); // Identifier table.
        empty_record_sequence(&mut encoder); // Property key table.
        empty_record_sequence(&mut encoder); // String table.
        0u32.encode(&mut encoder); // Constant count.
        Bytes(&[]).encode(&mut encoder);
        empty_record_sequence(&mut encoder); // Exception handlers.
        empty_record_sequence(&mut encoder); // Source map.
        empty_record_sequence(&mut encoder); // Local variables.

        match function_payload {
            Some(payload) => {
                1u32.encode(&mut encoder);
                encoder.align_to(align_of::<u16>());
                Bytes(&payload).encode(&mut encoder);
            }
            None => empty_record_sequence(&mut encoder),
        }

        empty_record_sequence(&mut encoder); // Class blueprints.

        DecodedCachedExecutableRecord {
            bytes: DecodedBytecodeBytes::Owned(encoder.finish()),
        }
    }

    fn function_payload(source_text_start: u32, source_text_end: u32) -> Vec<u8> {
        let mut encoder = Encoder::new();

        Option::<Utf16<'_>>::None.encode(&mut encoder); // Function name.
        source_text_start.encode(&mut encoder);
        source_text_end.encode(&mut encoder);
        0i32.encode(&mut encoder); // Function length.
        0u32.encode(&mut encoder); // Formal parameter count.
        (ast::FunctionKind::Normal as u8).encode(&mut encoder);
        false.encode(&mut encoder); // Strict mode.
        false.encode(&mut encoder); // Arrow function.
        false.encode(&mut encoder); // Simple parameter list.
        false.encode(&mut encoder); // Uses this.
        false.encode(&mut encoder); // Uses this from environment.
        Option::<(Utf16<'_>, bool)>::None.encode(&mut encoder); // Class field initializer name.
        FunctionSfdMetadata {
            uses_this: false,
            this_value_needs_environment_resolution: false,
            function_environment_needed: false,
            function_environment_bindings_count: 0,
            var_environment_bindings_count: 0,
            might_need_arguments: false,
            contains_eval: false,
        }
        .encode(&mut encoder);

        let empty_executable = cached_executable_with_shared_function(None);
        encoder.align_to(align_of::<u16>());
        Bytes(empty_executable.bytes.as_slice()).encode(&mut encoder);

        encoder.finish()
    }

    #[test]
    fn sequence_decode_rejects_lengths_larger_than_remaining_bytes() {
        let bytes = u32::MAX.to_le_bytes();

        let mut decoder = Decoder::new(&bytes, None);
        assert!(decoder.sequence_values(u8::decode).is_none());
    }

    #[test]
    fn sequence_decode_rejects_truncated_items_without_large_allocation() {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&4u32.to_le_bytes());
        bytes.extend_from_slice(&[1, 2, 3]);

        let mut decoder = Decoder::new(&bytes, None);
        assert!(decoder.sequence_values(u8::decode).is_none());
    }

    #[test]
    fn record_sequence_decode_rejects_impossible_count_without_large_allocation() {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&4u32.to_le_bytes());
        bytes.extend_from_slice(&1u32.to_le_bytes());
        bytes.push(0);

        let mut decoder = Decoder::new(&bytes, None);
        assert!(DecodedRecordSequence::decode(&mut decoder).is_none());
    }

    #[test]
    fn constant_table_decode_rejects_impossible_count_without_large_allocation() {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&4u32.to_le_bytes());
        bytes.extend_from_slice(&1u32.to_le_bytes());
        bytes.push(0);

        let mut decoder = Decoder::new(&bytes, None);
        assert!(ConstantTable::decode(&mut decoder).is_none());
    }

    #[test]
    fn decode_rejects_mismatched_source_hash_before_payload() {
        let stored_source_hash = [1u8; SOURCE_HASH_SIZE];
        let expected_source_hash = [2u8; SOURCE_HASH_SIZE];

        let mut bytes = Vec::new();
        bytes.extend_from_slice(MAGIC);
        bytes.extend_from_slice(&FORMAT_VERSION.to_le_bytes());
        bytes.push(ast::ProgramType::Script as u8);
        bytes.extend_from_slice(&stored_source_hash);

        assert!(decode_blob(&bytes, ast::ProgramType::Script, &expected_source_hash).is_none());
    }

    unsafe extern "C" fn ignore_foreign_owner(_: *mut c_void) {}

    #[test]
    fn utf16_decode_borrows_from_foreign_blob() {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&3u32.to_le_bytes());
        bytes.extend_from_slice(&0x41u16.to_le_bytes());
        bytes.extend_from_slice(&0x2262u16.to_le_bytes());
        bytes.extend_from_slice(&0x0391u16.to_le_bytes());

        let mut decoder = Decoder::new(
            &bytes,
            Some(ForeignBytecodeCacheBlobOwner {
                owner: std::ptr::null_mut(),
                free_owner: ignore_foreign_owner,
            }),
        );
        let decoded = DecodedUtf16String::decode(&mut decoder).unwrap();
        assert!(matches!(decoded, DecodedUtf16String::Foreign { .. }));
        assert_eq!(decoded.to_vec(), vec![0x41, 0x2262, 0x0391]);
    }

    #[test]
    fn cached_function_source_ranges_include_nested_functions() {
        let nested_function = function_payload(20, 21);
        let executable = cached_executable_with_shared_function(Some(nested_function));

        assert!(!executable.source_ranges_are_valid(10));
    }
}