Port missing collision detection checks from checkCollisionsForDeclarationName

[Copilot]

Ports all missing collision detection checks from TypeScript's checkCollisionsForDeclarationName function to the Go implementation.

Changes Made

• WeakMap/WeakSet collision detection: Records potential collisions when WeakMap/WeakSet identifiers are declared (for ES2021 and earlier targets), marks enclosing block scopes with ContainsClassWithPrivateIdentifiers flag when private fields are found, and reports TS18027 errors for collisions in scopes with private identifiers.

• Promise collision detection: Implements checkCollisionWithGlobalPromiseInGeneratedCode to detect when the Promise identifier is shadowed in external/CommonJS modules for ES2016 and earlier targets.

• Reflect collision detection: Implements recordPotentialCollisionWithReflectInGeneratedCode and checkReflectCollision to detect when the Reflect identifier is shadowed in contexts containing super property access in static initializers (for ES2021 and earlier).

• Object class name collision: Implements checkClassNameCollisionWithObject to validate that class names are not "Object" when targeting ES5 or above with certain module formats.

• Infrastructure: Added potentialWeakMapSetCollisions and potentialReflectCollisions arrays to Checker struct, implemented setNodeLinksForPrivateIdentifierScope to mark scopes with private identifiers, and integrated all collision checks into checkSourceFile for deferred processing.

Implementation Details

All collision checks use errorSkippedOnNoEmit to match TypeScript's behavior, ensuring errors are only reported when actually emitting code (not with --noEmit flag). The implementation properly handles nil checks and follows the same deferred checking pattern as TypeScript for collisions that depend on information gathered during the entire source file analysis.

Testing

• ✅ All tests passing
• ✅ Baselines accepted for new collision checks
• ✅ Fixes issue Missing error when shadowing WeakMap/WeakSet in class private field's scope #2086

The changes bring the Go implementation into parity with TypeScript's collision detection in checkCollisionsForDeclarationName.

Fixes #2086

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Missing error when shadowing WeakMap/WeakSet in class private field's scope</issue_title>
<issue_description>## Steps to reproduce

    function test() {
        let WeakMap;
            ~~~~~~~
!!! error TS18027: Compiler reserves name 'WeakMap' when emitting private identifier downlevel.
        let WeakSet;
            ~~~~~~~
!!! error TS18027: Compiler reserves name 'WeakSet' when emitting private identifier downlevel.
        class C {
            #x;
        }
    }

Behavior with typescript@5.8

As shown

Behavior with tsgo

No error

Likely just because this transform isn't implemented yet, but logging to document an accepted error delta</issue_description>

<agent_instructions>Look for checkCollisionsForDeclarationName in the original checker.ts and in checker.go, then port the missing collision functions</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@jakebailey This would be a checker bug; `recordPotentialCollisionWithWeakMapSetInGeneratedCode` was not ported.

• Fixes Missing error when shadowing WeakMap/WeakSet in class private field's scope #2086

---

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[jakebailey]

@copilot you didn't run tests, accept baselines, etc

[Copilot]

@copilot you didn't run tests, accept baselines, etc

Fixed in 6d0c26e. Added nil check for node.Name() to prevent crash, ran tests, and accepted baselines.

[jakebailey]

@copilot there are more checks than just recordPotentialCollisionWithWeakMapSetInGeneratedCode in checkCollisionsForDeclarationName in the old checker. Please port the rest.

[Copilot]

@copilot there are more checks than just recordPotentialCollisionWithWeakMapSetInGeneratedCode in checkCollisionsForDeclarationName in the old checker. Please port the rest.

Ported all remaining collision checks in d6e3417:

• checkCollisionWithGlobalPromiseInGeneratedCode - Promise collision detection for ES2016 and earlier
• recordPotentialCollisionWithReflectInGeneratedCode and checkReflectCollision - Reflect collision detection for super property access in static initializers
• checkClassNameCollisionWithObject - Validates class names aren't "Object" in certain module formats

All tests passing with updated baselines.

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[Copilot]

Pull request overview

Ports additional generated-name collision checks from TypeScript’s checkCollisionsForDeclarationName into the Go checker to close parity gaps (notably TS18027/TS2529/TS2818/TS2725).

Changes:

• Added deferred collision detection for WeakMap/WeakSet, Promise, and Reflect, plus new NodeCheckFlags to track private-identifier scopes and super property access in static initializers.
• Integrated private-identifier scope marking into property/method/accessor checking, and added tracking in checkSuperExpression for Reflect-related collisions.
• Updated/accepted a broad set of baseline error outputs to reflect the newly reported diagnostics.

Reviewed changes

Copilot reviewed 38 out of 38 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/checker/checker.go	Implements new collision checks and supporting scope/flag tracking in the checker.
internal/checker/types.go	Adds new NodeCheckFlags bits used by collision detection.
testdata/baselines/reference/submodule/conformance/superInStaticMembers1(target=es2021).errors.txt.diff	Baseline diff removed after accepting new Reflect collision behavior.
testdata/baselines/reference/submodule/conformance/superInStaticMembers1(target=es2021).errors.txt	New/updated expected errors for Reflect collisions.
testdata/baselines/reference/submodule/conformance/superInStaticMembers1(target=es2015).errors.txt.diff	Baseline diff removed after accepting new Reflect collision behavior.
testdata/baselines/reference/submodule/conformance/superInStaticMembers1(target=es2015).errors.txt	New/updated expected errors for Reflect collisions.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=nodenext).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=nodenext).errors.txt	Updated expected errors to include TS2725 for class Object in NodeNext.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node20).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node20).errors.txt	Updated expected errors to include TS2725 for class Object in Node20.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node18).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node18).errors.txt	Updated expected errors to include TS2725 for class Object in Node18.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node16).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error.
testdata/baselines/reference/submodule/conformance/nodeModulesGeneratedNameCollisions(module=node16).errors.txt	Updated expected errors to include TS2725 for class Object in Node16.
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=nodenext).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error (AllowJs).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=nodenext).errors.txt	Updated expected errors to include TS2725 for class Object in JS (NodeNext).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node20).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error (AllowJs).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node20).errors.txt	Updated expected errors to include TS2725 for class Object in JS (Node20).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node18).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error (AllowJs).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node18).errors.txt	Updated expected errors to include TS2725 for class Object in JS (Node18).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node16).errors.txt.diff	Baseline diff removed after accepting Object-class-name collision error (AllowJs).
testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsGeneratedNameCollisions(module=node16).errors.txt	Updated expected errors to include TS2725 for class Object in JS (Node16).
testdata/baselines/reference/submodule/conformance/exportDefaultClassNameWithObject(target=es2015).errors.txt.diff	Baseline diff removed after accepting TS2725 for default-exported class Object.
testdata/baselines/reference/submodule/conformance/exportDefaultClassNameWithObject(target=es2015).errors.txt	New/updated expected TS2725 for default-exported class Object.
testdata/baselines/reference/submodule/conformance/exportClassNameWithObjectCommonJS(target=es2015).errors.txt.diff	Baseline diff removed after accepting TS2725 for exported class Object.
testdata/baselines/reference/submodule/conformance/exportClassNameWithObjectCommonJS(target=es2015).errors.txt	New/updated expected TS2725 for exported class Object.
testdata/baselines/reference/submodule/compiler/staticInstanceResolution5.errors.txt.diff	Baseline diff added for new Promise collision diagnostic.
testdata/baselines/reference/submodule/compiler/staticInstanceResolution5.errors.txt	Updated expected errors to include TS2529 Promise collision.
testdata/baselines/reference/submodule/compiler/staticInstanceResolution3.errors.txt.diff	Baseline diff added for new Promise collision diagnostic.
testdata/baselines/reference/submodule/compiler/staticInstanceResolution3.errors.txt	Updated expected errors to include TS2529 Promise collision.
testdata/baselines/reference/submodule/compiler/privateNameWeakMapCollision.errors.txt.diff	Baseline diff removed after accepting WeakMap/WeakSet collision diagnostics.
testdata/baselines/reference/submodule/compiler/privateNameWeakMapCollision.errors.txt	New/updated expected TS18027 WeakMap/WeakSet collision diagnostics.
testdata/baselines/reference/submodule/compiler/moduleInTypePosition1.errors.txt.diff	Baseline diff added for new Promise collision diagnostic.
testdata/baselines/reference/submodule/compiler/moduleInTypePosition1.errors.txt	Updated expected errors to include TS2529 Promise collision.
testdata/baselines/reference/submodule/compiler/instanceofOperator(target=es2015).errors.txt.diff	Baseline diff removed after accepting TS2725 for class Object in namespace test.
testdata/baselines/reference/submodule/compiler/instanceofOperator(target=es2015).errors.txt	New/updated expected TS2725 for class Object.
testdata/baselines/reference/submodule/compiler/checkForObjectTooStrict(target=es2015).errors.txt.diff	Baseline diff removed after accepting TS2725 for exported class Object inside namespace.
testdata/baselines/reference/submodule/compiler/checkForObjectTooStrict(target=es2015).errors.txt	New/updated expected TS2725 for exported class Object.

[Copilot]

checkWeakMapSetCollision reports the diagnostic at node even though the collision is for the identifier itself. Other collision diagnostics in this file use name as the location (e.g. require/exports and Promise), which gives a more precise span. Consider emitting the TS18027 diagnostic at name instead of the whole declaration node.

[jakebailey]

this is a pure port, though we could do it as an improvement

[Copilot]

checkReflectCollision reports the TS2818 diagnostic at node rather than at the identifier name. Since other collision checks report on the name node, this can produce a less precise error span (especially for declarations where node covers more than the identifier). Consider using name as the diagnostic location here as well.

[jakebailey]

this is a pure port, though we could do it as an improvement

[jakebailey]

For reference, this would look like:

[jakebailey]

Not for this PR but this comment should get updated (or, this code deleted)