refactor(ast): Introduce flexible serialization encoding for AST #11100

quininer · 2025-09-18T08:25:25Z

Description:

Following our previous discussion, I am trying to introduce a self-describing serialization encoding for ast to replace #11069 .

Since serde is currently used for json serialization, it is hard to modify serde to support both json and binary encodings (due to the untagged and flatten attr). So I made our own Encode and Decode proc macro, which also facilitate unknown variant support.

I've done some simple benchmarks with a modified swc ast, and I believe we don't have an unacceptable performance loss relative to rkyv.
I'm using cbor4ii here, which I developed, so I'd prefer it if there's no performance difference. but it's easy to migrate to bincode or other scheme.

This also introduces an unknown feature for ecma_ast crate, which should only be enabled by the wasm plugin to ensure that old plugins can decode new AST.

BREAKING CHANGE:

This PR itself only introduces new encoding and will not cause any breakage. However, it may cause breakage when switch the wasm plugin communication scheme in future.

Related issue (if exists):

changeset-bot · 2025-09-18T08:25:32Z

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Latest commit: f23fdbf

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codspeed-hq · 2025-09-18T12:46:13Z

CodSpeed Performance Report

Merging #11100 will not alter performance

_{Comparing quininer:r/self-desc-encode (f23fdbf) with main (dba23f5)}

Summary

✅ 138 untouched

socket-security · 2025-09-19T03:46:18Z

No dependency changes detected. Learn more about Socket for GitHub.

👍 No dependency changes detected in pull request

**Description:** This is the split of #11100. Since we need to add unknown variants to the ast enum, this requires a lot of code changes to handle non-exhaustive matches. I'm doing this in a separate PR for review.

quininer · 2025-10-14T07:42:11Z

This also requires a serialization test, include unknown variants.

Since I'm busy with other work, it will be a little slower.

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github-actions · 2025-10-30T04:27:05Z

Binary Sizes

File	Size
`swc.linux-x64-gnu.node`	31M (32023392 bytes)

Commit: c4ed6d2

crates/jsdoc/src/ast.rs

crates/ast_node/src/encoding/encode.rs

crates/ast_node/src/encoding/mod.rs

crates/swc_common/src/lib.rs

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Copilot · 2025-10-31T07:32:51Z

crates/swc_common/tests/attr_interop.rs

    pub s: String,
 }

 #[ast_node("Tuple")]


The change from usize to u64 alters the semantics of the Tuple struct. On 32-bit platforms, usize is 32 bits while u64 is 64 bits, which could lead to different behavior. This appears to be unrelated to the encoding implementation and should be documented or justified.

Suggested change

#[ast_node("Tuple")]

#[ast_node("Tuple")]

// NOTE: We use `u64` instead of `usize` for cross-platform consistency and to avoid issues with serialization/deserialization on 32-bit vs 64-bit platforms. If you need platform-dependent sizing, consider using `usize` and document the rationale.

Copilot · 2025-10-31T07:32:52Z

crates/swc_common/src/serializer.rs

@@ -1,5 +1,5 @@
 #![allow(deprecated)]
-#![deprecated = "Not used by swc, and this will be removed with next breaking change"]
+


The deprecation attribute and warning comment were removed without explanation. If this module is no longer deprecated and is being actively used for CBOR encoding support, this should be documented in the PR description or in a code comment explaining why the deprecation was lifted.

Copilot · 2025-10-31T07:32:52Z

crates/swc_atoms/src/wtf8_atom.rs

+        // This is not sound, maybe Wtf8Buf should make bytes operations safe
+        Ok(Self(hstr::Wtf8Atom::from(unsafe {
+            Wtf8Buf::from_bytes_unchecked(s.0.into())
+        })))


The comment admits this is 'not sound' yet uses unsafe code without validation. CBOR decoding should validate that the bytes form valid WTF-8. Consider adding validation before the unsafe conversion or document why it's safe in this context.

Suggested change

// This is not sound, maybe Wtf8Buf should make bytes operations safe

Ok(Self(hstr::Wtf8Atom::from(unsafe {

Wtf8Buf::from_bytes_unchecked(s.0.into())

})))

// Validate that the bytes are valid WTF-8 before constructing Wtf8Buf

match Wtf8::from_bytes(s.0) {

Some(_) => Ok(Self(hstr::Wtf8Atom::from(Wtf8Buf::from_bytes_unchecked(s.0.into())))),

None => Err(cbor4ii::core::dec::Error::message("Invalid WTF-8 bytes")),

}

crates/swc_css_parser/tests/fixture/function/unknown/output.json

kdy1

Thank you so much for the hard work!

move to ast_node make encoding-impl optional fix fmt make css_ast fix tuple fix unknown fix fmt make html_ast make xml_ast make jsdoc fix fmt fix unit tag update visit fix parser make regexp_ast no unknown fix snap fix arbitrary encoding: ignore unknown field fix cfg fix enum struct derive

Refactor AST serialization to support flexible encoding.

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quininer force-pushed the r/self-desc-encode branch 2 times, most recently from c9d0a01 to de8261b Compare September 18, 2025 12:27

quininer force-pushed the r/self-desc-encode branch from de8261b to bc125dc Compare September 19, 2025 03:44

quininer force-pushed the r/self-desc-encode branch 12 times, most recently from 1b60f1d to c5fab18 Compare September 22, 2025 12:10

quininer mentioned this pull request Sep 22, 2025

refactor(ast_node): Make AST enums non_exhaustive #11115

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perf(plugin): hstr::Atom has very inefficient serialization/deserialization logic #11207

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kdy1 changed the title ~~refactor(ast): Introduce flexible serialization encoding for ast~~ refactor(ast): Introduce flexible serialization encoding for AST Oct 31, 2025

kdy1 enabled auto-merge (squash) October 31, 2025 07:44

quininer and others added 4 commits October 31, 2025 15:58

Add encoding-impl test

20d92c6

fix fmt

eed0dca

Update serialization encoding for AST

f23fdbf

Refactor AST serialization to support flexible encoding.

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kdy1 merged commit 8ad3647 into swc-project:main Oct 31, 2025
180 checks passed

quininer deleted the r/self-desc-encode branch October 31, 2025 10:02

	#[ast_node("Tuple")]
	#[ast_node("Tuple")]
	// NOTE: We use `u64` instead of `usize` for cross-platform consistency and to avoid issues with serialization/deserialization on 32-bit vs 64-bit platforms. If you need platform-dependent sizing, consider using `usize` and document the rationale.

		@@ -1,5 +1,5 @@
		#![allow(deprecated)]
		#![deprecated = "Not used by swc, and this will be removed with next breaking change"]

-        // This is not sound, maybe Wtf8Buf should make bytes operations safe
-        Ok(Self(hstr::Wtf8Atom::from(unsafe {
-            Wtf8Buf::from_bytes_unchecked(s.0.into())
-        })))
+        // Validate that the bytes are valid WTF-8 before constructing Wtf8Buf
+        match Wtf8::from_bytes(s.0) {
+            Some(_) => Ok(Self(hstr::Wtf8Atom::from(Wtf8Buf::from_bytes_unchecked(s.0.into())))),
+            None => Err(cbor4ii::core::dec::Error::message("Invalid WTF-8 bytes")),
+        }

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refactor(ast): Introduce flexible serialization encoding for AST #11100

refactor(ast): Introduce flexible serialization encoding for AST #11100

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Merging #11100 will not alter performance

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