GeezerVison

This PR is AI-generated from human-written test cases that demonstrate discrepancies between TypeScript typing and ES standard behaviour. The PR itself has also been reviewed by me before submission. Here are the main issues it addresses:

Closes: #35909

Two Symbol.for calls with the same key currently produces non-identical unique symbol types, so TypeScript rejects equality checks and assignments that succeed at runtime. This PR gives them the same registered-symbol type when their keys are the same literal.

Closes: #27524

Assigning a known symbol to another const currently widens its type to symbol, preventing the alias from serving as the same computed property key. This PR retains the symbol's narrow type through the const alias.

Closes: #55901

A const initialized with an assertion such as u as typeof u can still lose its unique symbol type, complicating uses such as isolated declaration emit. This PR preserves the asserted symbol identity in that const-like declaration.

Summary

• Add a RegisteredSymbol<Key> intrinsic and preserve literal registry keys in the return type of Symbol.for.
• Represent unresolved registry keys with a deferred symbol type, so separate generic calls do not receive one unsound unique-symbol identity.
• Preserve narrow unique symbol types in const-like declarations and allow const assertions on them.
• Emit and resolve symbol-keyed object properties using their registered and unique symbol types; serialize computed registered-symbol keys through their inferred types in declarations.
• Add compiler cases and accepted baselines for symbol typing, property access, and deferred registry keys.

Tests

• go -C ./tsc test -run='TestLocal/(registeredSymbolComputedNameDeclaration|registeredSymbolGenericRelations|registeredSymbolDeferredKey|registeredSymbolIntrinsic|registeredSymbolPropertyAccess|uniqueSymbolConstLikeWidening)\.ts$' ./internal/testrunner -count=1
• go -C ./tsc test ./internal/checker ./internal/api
• go -C ./tsc test -run='^TestLocal$' ./internal/testrunner -count=1

Related Work

Refs: #35562

This issue asks for symbols stored in an as const object to retain unique symbol types so they can be used as computed class property names. It relates to this PR's preservation of narrow symbol types in const-like contexts.

Refs: #37469

This issue proposes symbol-specific return types for functions and aliases of Symbol and Symbol.for, including a type tied to a global registry key. This PR addresses the registry-backed portion through RegisteredSymbol<Key>; it does not add a general new symbol return type.

Refs: #54778

This earlier PR proposed preventing readonly symbol values from widening, including cases involving indirect unique-symbol declaration emit. Its approach overlaps with this PR's const-like symbol preservation.

Refs: #60052

This merged PR relaxed restrictions on computed names in declarations and preserved computed names expressed as entity names during declaration emit. Those changes are relevant to representing and emitting the symbol-keyed properties handled here.

Co-authored-by: Codex [email protected]