Port non-baseline diagnostics tests

[gabritto]

This PR ports diagnostics fourslash tests. I think about 60% of tests that rely on verify.getXDiagnostics functions also rely on verify.codeFix though, which isn't ported, so the tests in this PR are the remaining 40%.

Note that in Strada, we had verify.getSyntacticDiagnostics, verify.getSemanticDiagnostics, and verify.getSuggestionDiagnostics, but in LSP there is no such distinction. I considered adding some information to the diagnostics we produce so that we could have those three kinds of testing functions, but that seemed not worth the effort, as I think long term we should think of diagnostics in the terms set by LSP, and there aren't that many diagnostics tests to start with.
So instead I've added VerifyDiagnostics, VerifySuggestionDiagnostics, and VerifyNonSuggestionDiagnostics. VerifyDiagnostics is for verifying all diagnostics for a file, and what I think we should use for new tests in Corsa, while VerifyNonSuggestionDiagnostics is like verify.getSyntacticDiagnostics + verify.getSemanticDiagnostics, and is implemented by filtering out the diagnostics sent by server that look like suggestion diagnostics, based on their severity and tags. This distinction was enough to get all but one ported test passing (modulo ones that fail for non-diagnostics reasons), and I think it's useful because it's common for a test to have unused identifier errors that don't really matter for the test, and those end up as suggestions.

I'll add baseline diagnostics in my next PR.

[Copilot]

Pull Request Overview

This PR ports fourslash diagnostic tests from TypeScript to the native Go implementation. It adds three new verification functions (VerifyDiagnostics, VerifyNonSuggestionDiagnostics, and VerifySuggestionDiagnostics) to enable testing of diagnostics in the language server protocol context, replacing the previous distinction between syntactic, semantic, and suggestion diagnostics with an LSP-based approach.

Key changes:

• Added diagnostic verification methods that filter diagnostics based on whether they are suggestions (using tags and severity)
• Updated the fourslash test converter script to parse diagnostic expectations from TypeScript tests
• Fixed a bug in selectLine to handle the last line of a file correctly
• Added approximately 30 new diagnostic tests

Reviewed Changes

Copilot reviewed 36 out of 36 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/fourslash/fourslash.go	Implements the three diagnostic verification functions, adds helper functions for filtering diagnostics and getting ranges in a file, fixes selectLine edge case, and adds diagnostic ignore options for deep equality checks
internal/fourslash/_scripts/convertFourslash.mts	Adds parsing logic for diagnostic verification commands (getSemanticDiagnostics, getSuggestionDiagnostics, getSyntacticDiagnostics) and converts them to Go test code
internal/fourslash/_scripts/manualTests.txt	Adds parserCorruptionAfterMapInClass to manual tests list
internal/fourslash/_scripts/failingTests.txt	Adds TestAutoImportModuleNone1 and TestJsDocAugmentsAndExtends to failing tests list
internal/fourslash/tests/manual/parserCorruptionAfterMapInClass_test.go	Manual test for parser corruption after map usage in class
internal/fourslash/tests/gen/*.go	29 generated diagnostic test files covering various scenarios including syntax errors, suggestion diagnostics, and semantic diagnostics

[jakebailey]

Suggestions don't necessarily have to have tags; e.g. if we were to do the "convert to ESM" fix, that would just be a hint, no tags. The tags just apply a visual change like strikethrough or greying out.

[gabritto]

This is an heuristic, as I think we don't have a consistent way of signaling a diagnostic is a suggestion, right? e.g. the unreachable code diagnostic has a tag, but its severity is Error.

[jakebailey]

It is so long as allowUnreachableCode is true; if it's undefined then it's Hint. But if that's the difference you're checking then yeah we can leave it.