Fix flaky diagnostic added by declaration emit for untyped module imports - #64479
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Fourslash now initializes the server with trackFlakyDiagnostics set to panic, so every textDocument/diagnostic request also emits the program and fails if the diagnostics differ before and after emit. This complements the compiler harness's pre/post-emit check, which compares separate programs by diagnostic count only and doesn't catch emit adding a diagnostic to an already-checked program. Add fourslash tests where declaration emit adds a "Could not find a declaration file for module" (7016) suggestion for an untyped import whose error was dropped by checking (plain JS file, @ts-expect-error, and an ES module under NodeNext).
…FromDeclaration getExternalModuleFileFromDeclaration is only used by emit (IsImportRequiredByAugmentation, module transforms) and by type-node reuse in the node builder. It resolved with the specifier as the error node, so for an untyped JS module it re-ran errorOnImplicitAnyModule with moduleNotFoundError == nil and recorded 7016 as a *suggestion*. Checking had already reported 7016 as an error, which was then dropped (plain JS file or @ts-expect-error), but suggestions bypass both filters, so the diagnostic appeared only after emit and tripped the LSP's flaky-diagnostic tracking. Resolve with ignoreErrors so these emit-time queries are free of diagnostic side effects. Fixes microsoft#64458
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| CodeLensShowLocationsCommandName: new(showCodeLensLocationsCommandName), | ||
| // Make every textDocument/diagnostic request also emit the program and fail if the | ||
| // diagnostics differ before and after emit, e.g. because the emit resolver added some. | ||
| TrackFlakyDiagnostics: new(lsproto.DiagnosticFlakeLogLevelPanic), |
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this "builds up" on microsoft/typescript-go#4526 and microsoft/typescript-go#4710 . It feels the same unconditional flaky diagnostic tracking can just be added to fourslash. And it makes it easier to write tests for this without going full in on server-level tests
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I feel wary of this a bit... Wesley Wigham (@weswigham)
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Hrm. compiler tests do do this check by default - but I guess the question is mostly just why these tests needs to be fourslash instead of compiler? Like, it's probably fine enough to turn on like this, I'm just surprised these tests aren't testable in the compiler harness, since it seems like they're just getting diagnostics? Fourslash tests are also a bit more sensitive to operation sequencing, so for fourslash it really should be opt-in - as some tests need specific server operation sequences to test the regressions they're looking for.
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Good shout. I couldnt reproduce this in the compiler tests initially - this relies on @captureSuggestions. But even with that, it didn't quite work (I tried that initially and gave up). To actually make it work the suggestion diagnostics had to be captured before emitting the declarations. I think this is a proper change regardless of the core fix here and made that change in:
dae525b
That finally reproduced the issue in compiler tests. But I've still kept TrackFlakyDiagnostics as a fourslash option in:
15553ab
And in the final version I dropped the fourslash tests for this completely as they were just replaced by the compiler tests.
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Copilot review overview
🟢 Approval recommended
The focused fix prevents emit-only diagnostic mutation and is covered across the reported import scenarios.
Review effort: Balanced
Findings: None
What changed in this PR
Prevents declaration emit/type printing from introducing diagnostics after checking.
Changes:
- Resolves emit-time module references without reporting errors.
- Enables flaky-diagnostic detection across Fourslash tests.
- Adds regression coverage for package, JavaScript, and NodeNext imports.
| File | Description |
|---|---|
tsc/internal/checker/checker.go |
Suppresses diagnostic side effects during emit-time resolution. |
tsc/internal/fourslash/fourslash.go |
Enables panic-level flaky-diagnostic tracking. |
tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule1_test.go |
Tests an untyped package import. |
tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule2_test.go |
Tests a relative JavaScript import. |
tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule3_test.go |
Tests a NodeNext .mjs import. |
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…ct pre-emit suggestions before declaration diagnostics
fixes crash reported here: #64458 (comment)