perf(linter/plugins): lazy deserialize comments array (#14637)

Part of #14564.

Deserialize `program.comments` lazily upon first access, instead of
eagerly, on assumption that most JS plugins won't access comments.

`deserializeWith` cleans up the buffer once deserializing AST is
complete, so we keep a local copy of the buffer in scope of the
`comments` getter, and restore it when the getter is triggered.

Buffers are reused, so the `if (localAstId !== astId)` check is required
to make sure the AST in the buffer is same AST i.e. that the getter
isn't accessed *after* the file has completed linting.

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: overlookmotel <theoverlookmotel@gmail.com>

Author: 3 people

apps/oxlint/src-js/generated/deserialize.js

@@ -1,7 +1,7 @@
 // Auto-generated code, DO NOT EDIT DIRECTLY!
 // To edit this generated file you have to edit `tasks/ast_tools/src/generators/raw_transfer.rs`.
 
-let uint8, uint32, float64, sourceText, sourceIsAscii, sourceByteLen, parent = null, getLoc;
+let uint8, uint32, float64, sourceText, sourceIsAscii, sourceByteLen, astId = 0, parent = null, getLoc;
 
 const textDecoder = new TextDecoder('utf-8', { ignoreBOM: true }),
   decodeStr = textDecoder.decode.bind(textDecoder),
@@ -38,13 +38,35 @@ function deserializeWith(buffer, sourceTextInput, sourceByteLenInput, getLocInpu
 
 function deserializeProgram(pos) {
   let end = deserializeU32(pos + 4),
+    refUint32 = uint32,
+    refUint8 = uint8,
+    refSourceText = sourceText,
+    localAstId = ++astId,
     program = parent = {
       __proto__: NodeProto,
       type: 'Program',
       body: null,
       sourceType: deserializeModuleKind(pos + 125),
       hashbang: null,
-      comments: deserializeVecComment(pos + 24),
+      get comments() {
+        if (localAstId !== astId) throw Error('Comments are only accessible while linting the file');
+        // Restore buffers
+        uint32 = refUint32;
+        uint8 = refUint8;
+        sourceText = refSourceText;
+        // Deserialize the comments
+        let comments = deserializeVecComment(pos + 24);
+        // Drop the references
+        refUint32 =
+          refUint8 =
+          refSourceText =
+          uint32 =
+          uint8 =
+          sourceText =
+            void 0;
+        Object.defineProperty(this, 'comments', { value: comments });
+        return comments;
+      },
       start: 0,
       end,
       range: [0, end],

crates/oxc_ast/src/serialize/mod.rs

@@ -124,12 +124,36 @@ impl Program<'_> {
     const start = IS_TS ? 0 : DESER[u32](POS_OFFSET.span.start),
         end = DESER[u32](POS_OFFSET.span.end);
 
+
+    /* IF COMMENTS */
+    // Buffers will be cleaned up after the main program is deserialized.
+    // We hold references here in case the comments need to be later accessed.
+    let refUint32 = uint32;
+    let refUint8 = uint8;
+    let refSourceText = sourceText;
+    const localAstId = ++astId;
+    /* END_IF */
+
     const program = parent = {
         type: 'Program',
         body: null,
         sourceType: DESER[ModuleKind](POS_OFFSET.source_type.module_kind),
         hashbang: null,
-        ...(COMMENTS && { comments: DESER[Vec<Comment>](POS_OFFSET.comments) }),
+        /* IF COMMENTS */
+        get comments() {
+            if (localAstId !== astId) throw new Error('Comments are only accessible while linting the file');
+            // Restore buffers
+            uint32 = refUint32;
+            uint8 = refUint8;
+            sourceText = refSourceText;
+            // Deserialize the comments
+            const comments = DESER[Vec<Comment>](POS_OFFSET.comments);
+            // Drop the references
+            refUint32 = refUint8 = refSourceText = uint32 = uint8 = sourceText = undefined;
+            Object.defineProperty(this, 'comments', { value: comments });
+            return comments;
+        },
+        /* END_IF */
         start,
         end,
         ...(RANGE && { range: [start, end] }),

tasks/ast_tools/src/generators/raw_transfer.rs

@@ -136,6 +136,7 @@ fn generate_deserializers(
     let mut code = format!("
         let uint8, uint32, float64, sourceText, sourceIsAscii, sourceByteLen;
 
+        let astId = 0;
         let parent = null;
         let getLoc;