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Reuse programs across edits to files with synthetic imports - #65104
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Since content mappers were added, ReuseProgram falls back to a full program build whenever the edited file needs a synthetic tslib or JSX runtime import. Every .tsx file in a project using the automatic JSX runtime has one, so each keystroke in such a file rebuilds the whole program in the language server. A synthetic import's resolution doesn't depend on the file's contents, so the program can be reused when the edit leaves the imports unchanged. The synthetic nodes are parented to the old file, so they are recreated for the new one, and include reasons now refer to synthetic imports by kind so they stay valid in the reused program.
Jake Bailey (jakebailey)
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November 2, 2026 17:44
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Nice find!
Jake Bailey (jakebailey)
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November 2, 2026 17:49
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🟡 Changes recommended
The reuse check permits cloning after a virtual extension changes from .cts to .mts, retaining stale CommonJS metadata and require-mode tslib resolution instead of rebuilding for ESM.
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What changed in this PR
This PR lets the language server reuse programs after edits that leave synthetic tslib and JSX runtime imports unchanged, avoiding full program rebuilds for common TSX edits.
Changes:
- Allow reuse when synthetic imports match, recreating their nodes for the updated files.
- Track synthetic imports by kind so file-inclusion reasons remain valid across reuse.
- Add coverage for reuse, synthetic-node ownership, diagnostics, and changed JSX import sources.
| File | Description |
|---|---|
tsc/internal/project/project_test.go |
Tests reuse with unchanged synthetic imports and fallback when the JSX import source changes. |
tsc/internal/compiler/program.go |
Checks synthetic-import compatibility and recreates nodes during reuse. |
tsc/internal/compiler/fileloader.go |
Records synthetic-import kinds and extracts shared node creation. |
tsc/internal/compiler/fileInclude.go |
Resolves synthetic-import inclusion reasons through the current program. |
Review effort: Balanced
Jake Bailey (jakebailey)
disabled auto-merge
November 2, 2026 17:58
A content mapper can switch a file's virtual extension between edits, for example from .cts to .mts. The parse options stay the same, so the program was reused with the file's old implied module format and the resolutions made under it, such as a require-mode tslib import.
Jake Bailey (jakebailey)
requested a review
from Andrew Branch (andrewbranch)
November 2, 2026 18:59
Andrew Branch (andrewbranch)
approved these changes
Nov 2, 2026
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Since content mappers were added, ReuseProgram falls back to a full program build whenever the edited file needs a synthetic tslib or JSX runtime import. Every .tsx file in a project using the automatic JSX runtime has one, so each keystroke in such a file rebuilds the whole program in the language server.
A synthetic import's resolution doesn't depend on the file's contents, so the program can be reused when the edit leaves the imports unchanged. The synthetic nodes are parented to the old file, so they are recreated for the new one, and include reasons now refer to synthetic imports by kind so they stay valid in the reused program.