Watch mode: clean up output files when source files are deleted

[DukeDeSouth]

Human View

Summary

Fixes microsoft/TypeScript#16057 — a 9-year-old bug (154 reactions) where tsc --watch does not delete corresponding output files when a source .ts file is deleted.

Problem

When using tsc --watch, deleting a source .ts file triggers a rebuild, but the corresponding output files (.js, .js.map, .d.ts, .d.ts.map) remain on disk. This causes:

• Test runners executing stale code
• Bundlers picking up dead modules
• Confusing import resolution errors

Solution

The watcher already detects file deletions (in hasBeenModified()), but never cleans up the orphaned outputs. This PR adds a cleanupDeletedOutputs() method that:

1. Captures deleted source file names in hasBeenModified() by comparing the previous file snapshot against the current state
2. Computes output paths for each deleted source file using the existing outputpaths package
3. Removes stale output files via vfs.FS.Remove()

The cleanup handles all output types:

• .js files
• .js.map (when sourceMap is enabled)
• .d.ts (when declaration is enabled)
• .d.ts.map (when declarationMap is enabled)

It respects outDir, declarationDir, noEmit, and other compiler options.

Changes

File	Change
internal/execute/watcher.go	Add deletedFiles field, capture deleted files in hasBeenModified(), add cleanupDeletedOutputs() method, call it from DoCycle()
internal/execute/tsctests/tscwatch_test.go	Add test case for file deletion cleanup
testdata/baselines/reference/tscWatch/commandLineWatch/watch-cleans-up-deleted-file-outputs.js	New baseline

Test

The new test case:

1. Creates a.ts and b.ts with outDir: "dist"
2. Initial build emits dist/a.js and dist/b.js
3. Deletes b.ts
4. Watch cycle rebuilds → verifies dist/b.js is removed

The baseline confirms the deletion: [/home/src/workspaces/project/dist/b.js] *deleted*

All existing watch mode tests pass without modification.

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AI View (DCCE Protocol v1.0)

Metadata

• Generator: Claude (Anthropic) via Cursor IDE
• Methodology: AI-assisted development with human oversight and review

AI Contribution Summary

• Solution design and implementation

Verification Steps Performed

1. Reproduced the reported issue
2. Analyzed source code to identify root cause
3. Implemented and tested the fix

Human Review Guidance

• Core changes are in: .js.map, .d.ts, .d.ts.map

Made with M7 Cursor

[DukeDeSouth]

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