Fix JSDoc @enum so the tagged name is a type as well as a value

[Xia Chao (bun-unsafe)]

Fixes #64003

JSDoc @enum on a const object did not introduce a type. The name was value-only, so @param {E} in the same file and const n: E = E.A against the emitted .d.ts both reported TS2749.

This parses @enum, reparses a type alias named after the host declaration, and merges it with the value. Declaration emit then includes export type E = … next to the existing const. JSDoc function(number): number is parsed as a function type so @enum {function(number): number} prints a valid signature (this also clears the old parse errors on {function(string): boolean} in typedefTagWrapping).

Emit is export type E = T plus export declare const E: { … }, not the 6.x namespace shape. The type+value contract is what consumers need (E in type position, E.A as a value).

Tests: jsDeclarationsEnumTag, enumTag*, jsFileESModuleWithEnumTag, typedefTagWrapping, smartSelection_JSDocTags9.

I used Copilot while writing this patch. I read the change, ran the tests above, and I will handle review myself.

[Copilot]

Pull request overview

Adds first-class JSDoc @enum type support and Closure-style function type parsing.

Changes:

• Adds JSDocEnumTag AST, parser, encoder, checker, and emit support.
• Synthesizes type aliases alongside enum values.
• Updates compiler and fourslash baselines.

Reviewed changes

Copilot reviewed 28 out of 33 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tsc/internal/parser/jsdoc.go	Parses enum tags and function types.
tsc/internal/parser/parser.go	Recognizes JSDoc function(...) types.
tsc/internal/parser/reparser.go	Synthesizes enum type aliases.
tsc/internal/checker/checker.go	Classifies enum tags in type space.
tsc/internal/checker/emitresolver.go	Handles enum-tag visibility.
tsc/internal/ast/ast.go	Integrates enum-tag accessors.
tsc/internal/ast/ast_generated.go	Adds generated enum-tag nodes.
tsc/internal/ast/kind_generated.go	Adds the enum-tag syntax kind.
tsc/internal/ast/kind_stringer_generated.go	Updates generated kind strings.
tsc/internal/ast/utilities.go	Enables enum-tag comments.
tsc/internal/api/encoder/encoder_generated.go	Encodes enum-tag children.
tsc/internal/api/encoder/decoder_generated.go	Decodes enum-tag children.
tools/scripts/tsc/ast.json	Defines the enum-tag AST schema.
smartSelection_JSDocTags9.baseline	Updates JSDoc selection output.
typedefTagWrapping.types	Records parsed function return types.
typedefTagWrapping.errors.txt	Removes obsolete parse errors.
jsDeclarationsEnumTag(target=es2015).types	Records enum aliases’ resolved types.
jsDeclarationsEnumTag(target=es2015).symbols	Records merged symbols.
jsDeclarationsEnumTag(target=es2015).js	Records emitted type aliases.
jsDeclarationsEnumTag(target=es2015).errors.txt	Removes value-only type errors.
enumTagUseBeforeDefCrash.types	Records the enum’s aliased type.
enumTagUseBeforeDefCrash.symbols	Records its merged symbol.
enumTagUseBeforeDefCrash.errors.txt	Removes the former type error.
enumTagOnExports.symbols	Records CommonJS merged symbols.
enumTagImported.types	Records imported enum types.
enumTagImported.symbols	Records imported merged symbols.
enumTagImported.errors.txt	Removes import/type errors.
enumTagCircularReference.symbols	Records the circular alias symbol.
enumTagCircularReference.errors.txt	Adds the circular-alias diagnostic.
enumTag.types	Records local enum alias types.
enumTag.symbols	Records local merged symbols.
enumTag.errors.txt	Removes value-only type errors.
jsFileESModuleWithEnumTag.symbols	Records merged ES-module symbols.

Files not reviewed (5)

• tsc/internal/api/encoder/decoder_generated.go: Generated file
• tsc/internal/api/encoder/encoder_generated.go: Generated file
• tsc/internal/ast/ast_generated.go: Generated file
• tsc/internal/ast/kind_generated.go: Generated file
• tsc/internal/ast/kind_stringer_generated.go: Generated file

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[Xia Chao (bun-unsafe)]

Thanks. The identifier check matches Strada nameForNamelessJSDocTypedef (element access only when the argument is an identifier).
Static exports["E"] / numeric literals are a reasonable follow-up (GetElementOrPropertyAccessName + identifier). I left that out of this PR so the @enum const/export case stays reviewable.

[Xia Chao (bun-unsafe)]

Thanks. This is a real remaining @enum hole: we only take the innermost name, so Host.UserMetrics.Action does not become a qualified type. jsEnumCrossFileExport.ts still reports TS2749.
This PR is scoped to a declaration-named const/export (export const E / .d.ts consumers). Wrapping the full static path like dotted @typedef is a follow-up. I can do it in this PR if you want it here.

[Xia Chao (bun-unsafe)]

@microsoft-github-policy-service agree

[Jake Bailey (jakebailey)]

Everything you're adding back was intentionally removed

https://github.com/microsoft/TypeScript/blob/main/tsc/CHANGES.md

[Xia Chao (bun-unsafe)]

You're right — I missed that @enum and Closure function(...) types are intentional Corsa removals, with @typedef / (s: T) => R as the substitute.

I'll close this PR. Sorry for the noise.

[Jake Bailey (jakebailey)]

Why did you choose to work on this? Does this personally affect you?

[Xia Chao (bun-unsafe)]

I was comparing 6.x vs 7 declaration emit on a small JSDoc fixture (@enum on a const, checkJs + declaration). The .d.ts left E value-only, so const n: E = E.A was TS2749, which I treated as a regression.
It does not affect a product I ship. I should have read CHANGES.md first — @enum / Closure function(...) are intentional removals, not a bug. Sorry for the noise.