fix(transformer/legacy-decorator): return runtime binding for design:type#22640
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…type (#22640) Closes #22227. Closes #22228. ## Summary - Switch `design:type` / `design:paramtypes` / `design:returntype` emit from `typeof X === "function" ? X : Object` to `typeof X === "undefined" ? Object : X`, matching SWC and Babel. Cross-file imported enums and namespace-imported enums (`NS.E`) now return the actual enum object instead of silently degrading to `Object` — consumers like type-graphql, typeorm, NestJS Swagger, AutoMapper, and class-validator can introspect via `Object.values()`. - Cases where the runtime binding is genuinely missing still fall back to `Object` (stale ambient declarations, erased type imports, unresolved references), so existing behavior is preserved everywhere else. - See #14740 for the design rationale: matching SWC/Babel rather than tsc's primitive-type emit (which requires cross-file type information OXC doesn't have). - Conformance: 5 existing fixtures updated for the new emit shape, 6 new fixtures cover the bug paths and predicate boundaries; no `Output mismatch` regressions. ## Example Input: ```ts import { StringEnum } from './enums'; class Source { @dec value!: StringEnum; } ``` Before: ```js // design:type === Object — StringEnum is an enum object, typeof !== "function" babelHelpers.decorateMetadata("design:type", typeof (_ref = typeof StringEnum !== "undefined" && StringEnum) === "function" ? _ref : Object) ``` After: ```js // design:type === StringEnum (the enum object — introspectable via Object.values) babelHelpers.decorateMetadata("design:type", typeof StringEnum === "undefined" ? Object : StringEnum) ``` ## Note on the SWC enum-metadata debate [swc-project/swc#11033](swc-project/swc#11033) argues SWC's emit is wrong for cross-file enums — the runtime returns the enum object (an `{...}`) rather than `Number` / `String` / `Object` as tsc would. This PR adopts the same emit shape SWC and Babel use, so it has the same property: cross-file enum metadata is the enum binding itself, not a primitive constructor. OXC chose this side of the debate deliberately in #14740 — returning the enum object is what type-graphql, typeorm, NestJS Swagger, AutoMapper, and class-validator depend on to introspect enum members. Matching tsc's primitive emit would require cross-file type information OXC doesn't have, and would unblock no real consumer. If TypeScript publishes a position on what non-type-checker transformers should emit, this can be revisited. AI disclosure: drafted with Claude Code, reviewed manually.
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I'd recommend adding an option that is disabled by default as this is also treated as a bug in the babel plugin (leonardfactory/babel-plugin-transform-typescript-metadata#11).
(so that we align with typescript by default)
This was in mind, actually. I chose to align back to SWC and Babel as they have already worked well for a long while and got a bare identifier actually good as they could use it to check and do something special they want. I just looked at the issue you mentioned; I think even the original implementation could produce a wrong type. In that issue example, it should be a It is a trade-off, but I am not opposed to adding an option for this if it proves to be very useful. I am happy to do it. |
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IMO the behavior is inconsistent and confusing. That said, the decorator metadata will be fading out anyways (microsoft/TypeScript#57533 (comment)), so my opinion is not so strong. |
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I guess discouraging the use of the feature + explaining the inconsistent behavior at https://oxc.rs/docs/guide/usage/transformer/typescript.html#decorators would help the users. |
### 🚀 Features - e857b0c napi/minify: Expose legalComments option and result (#20370) (Boshen) - 661132d parser: More friendly error messages for rest assignment target and rest binding element (#22719) (sapphi-red) - ee659b6 transformer/legacy-decorator: Add `strictNullChecks` option for nullable-union design:type (#22266) (Kyle Cannon) ### 🐛 Bug Fixes - e1d064e transformer/class-properties: Reparent lifted private method helpers (#22716) (Cameron) - 4ac0fca minifier: Preserve `0 && (module.exports = { ... })` cjs-module-lexer hint (#22729) (Dunqing) - 40ff611 minifier: Mark peephole loop changed when dropping dead-after-throw statement (#22722) (Dunqing) - 2f7b210 codegen: Emit pife-arrow/function leading comments inside the wrap (#22720) (Dunqing) - e184f74 parser: Improve invalid `import` property access diagnostic (#22693) (camc314) - 7baed9c transformer/private-method: Clear inherited strict flags (#22508) (camc314) - a9ad27e parser: Keep annotation comments leading without preceding newline (#22711) (Dunqing) - 9ea4d64 minifier: Re-evaluate pure/no-side-effects flags after peephole inlining (#22595) (Dunqing) - 07afbb6 minifier: Drop empty-body IIFE wrapper when called with arguments (#22589) (Dunqing) - fa7c463 semantic: Correct TS enum member symbol spans (#22689) (camc314) - 26b9396 semantic: Resolve parameter decorators outside parameter scope (#22623) (camc314) - b284045 parser: Switch to module goal eagerly on `export` (#22684) (Boshen) - dfa931d semantic: Propagate unresolved auto-increment enum value instead of defaulting to 0 (#22646) (Dunqing) - 69a6ba6 transformer/legacy-decorator: Emit Array for ReadonlyArray<T> in decorator metadata (#22265) (Kyle Cannon) - e421ef0 transformer/legacy-decorator: Return runtime binding for design:type (#22640) (Dunqing) - d61e1d7 codegen: Preserve verbatim text of pure/no-side-effects comments (#22525) (Dunqing) - 702b14e minifier: Preserve IIFE structure in DCE-only mode (#22547) (Dunqing) - 917da24 parser: Apply PURE comment through member-access chains (#22566) (Dunqing) - a069b1c codegen: Preserve quotes for cjs-module-lexer equality strings (#22551) (Dunqing) ### ⚡ Performance - 2f623b0 semantic: Skip unresolved checks for re-exports (#22660) (camc314) - 0d9553d semantic: Early-exit `check_object_expression` for objects with <2 properties (#22668) (Dunqing) - d721ad9 semantic: Use direct grandparent lookup for TS type parameters (#22658) (camc314) - 0aff288 semantic: Reorder numeric literal strict mode checks (#22657) (camc314) - 4d5ddb1 semantic: Reorder binding identifier checks (#22656) (camc314) - e32acd8 semantic: Reorder identifier ambient binding check (#22653) (camc314) - 09fe178 semantic: Reorder ident reference strict mode check (#22652) (camc314) - 4b6add2 semantic: Avoid duplicate ident clone for bindings (#22663) (camc314) - 82f9662 parser: Check identifier kind before context flag (#22662) (camc314) - d7cd951 parser: Fast path identifier parsing and inline operator helpers (#22650) (Boshen) - 7b84314 semantic: Use direct byte access for numeric leading-zero check (#22642) (camc314) - 0345a31 semantic: Pre-size class elements hash map (#22618) (camc314) - 04d3065 minifier: Drop per-call buffers in try_fold_concat (#22596) (Dunqing) - 4f289f1 semantic: Resolve_references_for_current_scope without a temp Vec (#22599) (Dunqing) - e862c15 semantic: Avoid heap alloc for var hoist scope ids (#22603) (Dunqing) - 8ff8674 semantic: Early return if `excess` is `0` in `Stats::increase_by` (#22616) (camc314) - 7a4120e semantic: Pre-reserve unresolved_references using Stats::references (#22580) (Dunqing) Co-authored-by: Dunqing <[email protected]>
2 participants
Closes #22227.
Closes #22228.
Summary
design:type/design:paramtypes/design:returntypeemit fromtypeof X === "function" ? X : Objecttotypeof X === "undefined" ? Object : X, matching SWC and Babel. Cross-file imported enums and namespace-imported enums (NS.E) now return the actual enum object instead of silently degrading toObject— consumers like type-graphql, typeorm, NestJS Swagger, AutoMapper, and class-validator can introspect viaObject.values().Object(stale ambient declarations, erased type imports, unresolved references), so existing behavior is preserved everywhere else.Output mismatchregressions.Example
Input:
Before:
After:
Note on the SWC enum-metadata debate
swc-project/swc#11033 argues SWC's emit is wrong for cross-file enums — the runtime returns the enum object (an
{...}) rather thanNumber/String/Objectas tsc would. This PR adopts the same emit shape SWC and Babel use, so it has the same property: cross-file enum metadata is the enum binding itself, not a primitive constructor.OXC chose this side of the debate deliberately in #14740 — returning the enum object is what type-graphql, typeorm, NestJS Swagger, AutoMapper, and class-validator depend on to introspect enum members. Matching tsc's primitive emit would require cross-file type information OXC doesn't have, and would unblock no real consumer. If TypeScript publishes a position on what non-type-checker transformers should emit, this can be revisited.
AI disclosure: drafted with Claude Code, reviewed manually.