fix(es/typescript): Handle TypeScript expressions in enum transformation by magic-akari · Pull Request #11769 · swc-project/swc

magic-akari · 2026-04-06T13:26:19Z

Description:

BREAKING CHANGE:

Related issue (if exists):

Closes: Typescript enum value with as syntax cause swc crash #11761

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github-actions · 2026-04-06T13:35:27Z

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`swc.linux-x64-gnu.node`	28M (29100488 bytes)

Commit: 2093266

codspeed-hq · 2026-04-06T13:38:44Z

Merging this PR will not alter performance

✅ 219 untouched benchmarks

_{Comparing magic-akari:fix/issue-11761 (00d0558) with main (236eff0)¹}

No successful run was found on main (fff1426) during the generation of this report, so 236eff0 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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crates/swc_ecma_transforms_typescript/src/transform.rs

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Pull request overview

Fixes a crash when transforming TypeScript enums whose member initializers include TS-only expression wrappers (e.g. as any), by unwrapping/stripping those wrappers during enum value computation and enum emission.

Changes:

Unwrap TS expression wrappers (as, non-null, type assertions, satisfies, etc.) when computing enum member values.
Visit/transform opaque enum initializer expressions during enum emission so TS-only syntax is stripped before codegen.
Add regression tests for TS-wrapped and complex enum initializers; update existing fixture outputs to match new behavior.

Reviewed changes

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Show a summary per file

File	Description
crates/swc_ecma_transforms_typescript/src/ts_enum.rs	Unwraps TS expression wrappers when computing enum member values.
crates/swc_ecma_transforms_typescript/src/transform.rs	Visits opaque enum initializer expressions and tracks opacity during enum emission.
crates/swc_ecma_transforms_typescript/tests/strip.rs	Adds new enum-related regression tests.
crates/swc_ecma_transforms_typescript/tests/swc_snapshots/tests/strip.rs/*	Adds snapshots for new regression tests.
crates/swc_ecma_transforms_typescript/tests/fixture/issue-3001/*/output.js	Updates expected fixture output due to new enum-expression processing/inlining.

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...cma_transforms_typescript/tests/__swc_snapshots__/tests/strip.rs/ts_enum_with_nested_enum.js

crates/swc_ecma_transforms_typescript/src/transform.rs

…m logic

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crates/swc_ecma_transforms_typescript/src/transform.rs

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crates/swc_ecma_transforms_typescript/src/ts_enum.rs

magic-akari · 2026-04-07T12:27:56Z

crates/swc_ecma_transforms_base/src/resolver/mod.rs

+            // Intentionally do not predeclare enum members in the resolver.
+            // Enum initializers may reference other members, including quoted names whose
+            // text is a valid identifier:
+            //
+            // ```TypeScript
+            //   enum E {
+            //       A = "A",
+            //       "B" = "B",
+            //       C = (() => { console.log(A, B); })(),
+            //   }
+            // ```
+            //
+            // We keep those references unresolved here so the TypeScript enum transform
+            // can rewrite them using semantic.enum_record.


Another approach would be to mark all of them with contexts, like this:

enum E#2 { A#4 = "A", "B"#4 = "B", C = (() => { console#1.log(A#4, B#4); })(), }

This way, during the subsequent enum transformation process, we could directly compare IDs to perform correct replacements.

However, SWC's current design doesn't allocate contexts for string enum members, so this approach doesn't work. We have to settle for the alternative: not marking any of them.

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crates/swc_ecma_transforms_typescript/src/ts_enum.rs

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crates/swc_ecma_transforms_typescript/src/transform.rs

crates/swc_ecma_transforms_typescript/src/ts_enum.rs

crates/swc/tests/tsc-references/constEnum2.1.normal.js

crates/swc/tests/tsc-references/constEnum2.2.minified.js

magic-akari · 2026-04-07T14:09:20Z

crates/swc_ecma_transforms_base/src/resolver/mod.rs

+            //
+            // We keep those references unresolved here so the TypeScript enum transform
+            // can rewrite them using semantic.enum_record.
+            child.current.mark = self.config.unresolved_mark;


Please review this part carefully.
I am unsure if this implementation represents the correct direction for the fix.
@swc-project/core

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crates/swc_ecma_transforms_base/src/resolver/mod.rs

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crates/swc_ecma_transforms_typescript/src/ts_enum.rs

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crates/swc_ecma_transforms_typescript/src/ts_enum.rs

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chatgpt-codex-connector · 2026-04-07T18:11:13Z

crates/swc_ecma_transforms_typescript/src/transform.rs

+                    let TsEnumRecordValue::Opaque(mut e) = enum_computer.compute(e) else {
+                        unreachable!();


Avoid panicking when recomputed enum value becomes const

This unreachable!() can be hit for validly parsed enums where the semantic pass stored an initializer as Opaque, but the second pass recomputes it as a constant using the full enum record. For example, enum E { A = B, B = 1 } records A as opaque during semantic analysis (because B is not known yet), then enum_computer.compute returns Number(1) here, so the destructuring fails and the transform panics instead of emitting code. The same crash pattern applies to forward references across merged enum declarations.

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Copilot · 2026-04-07T18:13:47Z

crates/swc_ecma_transforms_typescript/src/transform.rs

+        let member_names = self
+            .semantic
+            .enum_record
+            .keys()
+            .filter(|k| k.enum_id == id.to_id())
+            .map(|k| k.member_name.clone())
+            .collect();
+
+        let enum_computer = EnumValueComputer {
+            enum_id: &id.to_id(),
+            unresolved_ctxt: self.unresolved_ctxt,
+            record: &self.semantic.enum_record,
+        };


EnumValueComputer { enum_id: &id.to_id(), .. } takes a reference to a temporary Id produced by to_id(). This will not live long enough and is expected to fail to compile (temporary dropped while borrowed). Bind let enum_id = id.to_id(); once and pass enum_id: &enum_id (and reuse enum_id in the nearby .filter(|k| k.enum_id == ...) / TsEnumRecordKey construction to avoid repeated to_id() calls).

Copilot · 2026-04-07T18:13:48Z

crates/swc_ecma_transforms_typescript/src/transform.rs

+                    };
+                    e.visit_mut_with(&mut RefRewriter {
+                        query: EnumMemberRefQuery {
+                            enum_id: &id.to_id(),
+                            member_names: &member_names,
+                            unresolved_ctxt: self.unresolved_ctxt,
+                        },
+                    });


EnumMemberRefQuery { enum_id: &id.to_id(), .. } also borrows a temporary Id. After introducing a local enum_id: Id (e.g. let enum_id = id.to_id();), pass enum_id: &enum_id here as well to avoid borrowing a temporary and to ensure the reference outlives the rewriter.

fix(es/typescript): Handle TypeScript expressions in enum transformation

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chore: update test cases

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magic-akari force-pushed the fix/issue-11761 branch from 75b4daa to c9ea557 Compare April 6, 2026 13:37

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refactor(es/typescript): simplify enum value computation and transfor…

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fix(typescript): Handle enum member references correctly

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fix: clippy issue

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fix(es/typescript): handle enum member names in resolver

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		let TsEnumRecordValue::Opaque(mut e) = enum_computer.compute(e) else {
		unreachable!();

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