Backport #3971: fix(swc-plugin): register class expressions via an IIFE instead of by name - #4013
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… name (#3971) * fix(swc-plugin): register class expressions via an IIFE and reject unnameable classes Class expressions with "use step" methods or custom serialization were registered by module-level statements referencing the class by name. When no module-scope binding could be resolved the plugin fell back to a placeholder `AnonymousClass` identifier, which is a guaranteed ReferenceError at module evaluation (#3929). Other shapes were silently wrong as well: `var A = class {}, B = class {}` registered A's steps under B, `X = class {}` assignments and classes nested inside functions emitted unresolvable references. Class expressions are now wrapped in a single IIFE that receives the class, performs every registration recorded for it, and returns it, so the registration no longer depends on a name being in scope. The class name is still needed for step/class IDs and is derived from the assigned variable, the class's own identifier, or the property key it is assigned to (`exports.Foo = class {}`, `{ Foo: class {} }`). When none is available, or the class is declared inside a function, the plugin emits a compile error instead of broken code. Class declarations keep their existing module-level output; the emitters were factored so both paths share the same statement builders. * fix(swc-plugin): generate names for anonymous class expressions instead of erroring With registration happening inside the IIFE, an anonymous class expression in a position that provides no name (`foo(class { ... })`, an array element, a conditional branch) only needs a name for its step/class IDs. Generate a deterministic `AnonymousClass<N>`, counting only anonymous classes that have something to register, instead of rejecting them. Classes declared inside a function remain an error. Dead-code elimination now keeps module-level declarations whose initializer contains a wrapped class expression: evaluating the initializer is what registers the class, and the binding may be otherwise unreferenced. Signed-off-by: Nathan Rajlich <n@n8.io>
🦋 Changeset detectedLatest commit: 630795b The changes in this PR will be included in the next version bump. This PR includes changesets to release 17 packages
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🧪 E2E Test Results❌ Some tests failed Summary
❌ Failed Tests🌍 Community Worlds (106 failed)redis (21 failed):
turso (85 failed):
Details by Category✅ ▲ Vercel Production
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Automated backport of #3971 to
stable(backport job run).AI recommendation: This is a correctness fix to code generation that exists on
stable(packages/swc-plugin-workflowis fully present there): class expressions were registered by module-level statements referencing a name that may not be in scope, emitting a guaranteedReferenceError(AnonymousClass is not defined) and, in multi-declarator cases, registering one class's steps under another class's name. The changeset is apatchand the change is scoped to the plugin's emitted registration code plus fixtures/spec; the only behavior addition (a compile error for classes declared inside functions) replaces output that could only ever throw at module evaluation. Reviewers should note it is a sizable codegen refactor, so the 133 fixtures/24 error cases are the thing to verify onstable.Merge conflicts were resolved by AI (opencode with
anthropic/claude-opus-5). Please review the conflict resolution carefully before merging.