refactor(napi/parser): raw transfer: introduce metadata struct (#12269)

Pure refactor. Introduce a `RawTransferMetadata` struct to hold metadata that gets written to end of buffer. Codegen use knowledge of memory layout of this struct to generate constants added in #12268. This is more robust than manually calculating offsets.

Author: overlookmotel

crates/oxc_ast_macros/src/generated/structs.rs

@@ -3,8 +3,8 @@
 
 const BUFFER_SIZE = 2147483648,
   BUFFER_ALIGN = 4294967296,
-  DATA_POINTER_POS_32 = 536870908,
-  IS_TS_FLAG_POS = 2147483636,
+  DATA_POINTER_POS_32 = 536870910,
+  IS_TS_FLAG_POS = 2147483644,
   PROGRAM_OFFSET = 0;
 
 module.exports = {

napi/parser/generated/constants.js

@@ -20,7 +20,7 @@ function deserialize(buffer, sourceTextInput, sourceLenInput) {
   sourceLen = sourceLenInput;
   sourceIsAscii = sourceText.length === sourceLen;
 
-  const data = deserializeRawTransferData(uint32[536870908]);
+  const data = deserializeRawTransferData(uint32[536870910]);
 
   uint8 =
     uint32 =

napi/parser/generated/deserialize/js.js

@@ -20,7 +20,7 @@ function deserialize(buffer, sourceTextInput, sourceLenInput) {
   sourceLen = sourceLenInput;
   sourceIsAscii = sourceText.length === sourceLen;
 
-  const data = deserializeRawTransferData(uint32[536870908]);
+  const data = deserializeRawTransferData(uint32[536870910]);
 
   uint8 =
     uint32 =

napi/parser/generated/deserialize/ts.js

@@ -17,6 +17,13 @@ const _: () = {
     assert!(offset_of!(RawTransferData, module) == 152);
     assert!(offset_of!(RawTransferData, errors) == 256);
 
+    // Padding: 3 bytes
+    assert!(size_of::<RawTransferMetadata>() == 16);
+    assert!(align_of::<RawTransferMetadata>() == 8);
+    assert!(offset_of!(RawTransferMetadata, data_offset) == 8);
+    assert!(offset_of!(RawTransferMetadata, is_ts) == 12);
+    assert!(offset_of!(RawTransferMetadata, _padding) == 0);
+
     // Padding: 7 bytes
     assert!(size_of::<Error>() == 80);
     assert!(align_of::<Error>() == 8);
@@ -68,6 +75,13 @@ const _: () = {
     assert!(offset_of!(RawTransferData, module) == 104);
     assert!(offset_of!(RawTransferData, errors) == 172);
 
+    // Padding: 3 bytes
+    assert!(size_of::<RawTransferMetadata>() == 16);
+    assert!(align_of::<RawTransferMetadata>() == 8);
+    assert!(offset_of!(RawTransferMetadata, data_offset) == 8);
+    assert!(offset_of!(RawTransferMetadata, is_ts) == 12);
+    assert!(offset_of!(RawTransferMetadata, _padding) == 0);
+
     // Padding: 3 bytes
     assert!(size_of::<Error>() == 44);
     assert!(align_of::<Error>() == 4);

napi/parser/src/generated/assert_layouts.rs

@@ -20,7 +20,7 @@ use oxc_napi::get_source_type;
 use crate::{
     AstType, ParserOptions, get_ast_type, parse,
     raw_transfer_constants::{BUFFER_ALIGN, BUFFER_SIZE},
-    raw_transfer_types::{EcmaScriptModule, Error, RawTransferData},
+    raw_transfer_types::{EcmaScriptModule, Error, RawTransferData, RawTransferMetadata},
 };
 
 // For raw transfer, use a buffer 2 GiB in size, with 4 GiB alignment.
@@ -179,10 +179,10 @@ unsafe fn parse_raw_impl(
     assert!(is_multiple_of(buffer_ptr as usize, BUFFER_ALIGN));
 
     // Get offsets and size of data region to be managed by arena allocator.
-    // Leave space for source before it, and 16 bytes for metadata after it.
+    // Leave space for source before it, and space for metadata after it.
     // Metadata actually only takes 5 bytes, but round everything up to multiple of 16,
     // as `bumpalo` requires that alignment.
-    const METADATA_SIZE: usize = 16;
+    const METADATA_SIZE: usize = size_of::<RawTransferMetadata>();
     const {
         assert!(METADATA_SIZE >= BUMP_ALIGN);
         assert!(is_multiple_of(METADATA_SIZE, BUMP_ALIGN));
@@ -271,15 +271,16 @@ unsafe fn parse_raw_impl(
         ptr::from_ref(data).cast::<u8>()
     };
 
-    // Write offset of `RawTransferData` and `bool` representing AST type into end of buffer
+    // Write metadata into end of buffer
     #[allow(clippy::cast_possible_truncation)]
-    let data_offset = data_ptr as u32;
+    let metadata = RawTransferMetadata::new(data_ptr as u32, ast_type == AstType::TypeScript);
     const METADATA_OFFSET: usize = BUFFER_SIZE - METADATA_SIZE;
-    // SAFETY: `METADATA_OFFSET` is less than length of `buffer`
+    const _: () = assert!(is_multiple_of(METADATA_OFFSET, BUMP_ALIGN));
+    // SAFETY: `METADATA_OFFSET` is less than length of `buffer`.
+    // `METADATA_OFFSET` is aligned on 16.
     #[expect(clippy::cast_ptr_alignment)]
     unsafe {
-        buffer_ptr.add(METADATA_OFFSET).cast::<u32>().write(data_offset);
-        buffer_ptr.add(METADATA_OFFSET + 4).cast::<bool>().write(ast_type == AstType::TypeScript);
+        buffer_ptr.add(METADATA_OFFSET).cast::<RawTransferMetadata>().write(metadata);
     }
 }
 

napi/parser/src/raw_transfer.rs

@@ -25,6 +25,23 @@ pub struct RawTransferData<'a> {
     pub errors: Vec<'a, Error<'a>>,
 }
 
+/// Metadata written to end of buffer.
+#[ast]
+pub struct RawTransferMetadata {
+    /// Offset of `RawTransferData` within buffer.
+    pub data_offset: u32,
+    /// `true` if AST is TypeScript.
+    pub is_ts: bool,
+    /// Padding to pad struct to size 16.
+    pub(crate) _padding: u64,
+}
+
+impl RawTransferMetadata {
+    pub fn new(data_offset: u32, is_ts: bool) -> Self {
+        Self { data_offset, is_ts, _padding: 0 }
+    }
+}
+
 // Errors.
 //
 // These types and the `From` / `FromIn` impls mirror the implementation in `types.rs`

napi/parser/src/raw_transfer_types.rs

@@ -32,10 +32,6 @@ const BUFFER_SIZE: u32 = 1 << 31; // 2 GiB
 const _: () = assert!(BUFFER_SIZE % 16 == 0);
 /// Alignment of raw transfer buffer.
 const BUFFER_ALIGN: u64 = 1 << 32; // 4 GiB
-/// Size of metadata written to end of buffer.
-const METADATA_SIZE: u32 = 16;
-/// Offset of flag for whether AST is TypeScript or not, relative to start of metadata.
-const IS_TS_FLAG_OFFSET: u32 = 4;
 
 // Offsets of `Vec`'s fields.
 // `Vec` is `#[repr(transparent)]` and `RawVec` is `#[repr(C)]`, so these offsets are fixed.
@@ -1020,9 +1016,11 @@ fn generate_constants(consts: Constants) -> (String, TokenStream) {
 
 /// Calculate constants.
 fn get_constants(schema: &Schema) -> Constants {
-    let metadata_pos = BUFFER_SIZE - METADATA_SIZE;
-    let data_pointer_pos_32 = metadata_pos / 4;
-    let is_ts_pos = metadata_pos + IS_TS_FLAG_OFFSET;
+    let metadata_struct = schema.type_by_name("RawTransferMetadata").as_struct().unwrap();
+    let metadata_pos = BUFFER_SIZE - metadata_struct.layout_64().size;
+    let data_pointer_pos = metadata_pos + metadata_struct.field_by_name("data_offset").offset_64();
+    let data_pointer_pos_32 = data_pointer_pos / 4;
+    let is_ts_pos = metadata_pos + metadata_struct.field_by_name("is_ts").offset_64();
 
     let program_offset = schema
         .type_by_name("RawTransferData")