Add test reproducing panic on out-of-bounds textDocument/definition request

[Copilot]

The LSP server panics when receiving a textDocument/definition request with a line number exceeding the file's line count. This occurs during client/server synchronization issues where the client's position data is stale.

Changes

• Test: Added TestPanicOnOutOfBoundsDefinition that sends a definition request for line 65 in an 8-line file
• Helper: Added SendDefinitionRequestAtPosition() to fourslash framework to bypass bounds checking for error handling tests

Current Behavior

panic: bad line number. Line: 65, lineMap length: 8
at LineAndCharacterToPosition (converters.go:143)

The server recovers and returns InternalError (-32603). The test fails as expected, documenting the bug without fixing it.

// Test simulates stale client position
f.SendDefinitionRequestAtPosition(t, 65, 24)
// File only has 8 lines - should handle gracefully, not panic

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Panic on textDocument/definition</issue_title>
<issue_description>## Stack trace

panic handling request textDocument/definition bad line number. Line: 65, lineMap length: 33 goroutine 74379 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:26 +0x5e
github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0xc0000f4dc0, 0xc05d9571d0)
	github.com/microsoft/typescript-go/internal/lsp/server.go:532 +0x58
panic({0x7ff76dc5a4c0?, 0xc02a3d9970?})
	runtime/panic.go:783 +0x132
github.com/microsoft/typescript-go/internal/ls.(*Converters).LineAndCharacterToPosition(0xc025592360, {0x7ff76dfe4430, 0xc03fbe7608}, {0x0?, 0x0?})
	github.com/microsoft/typescript-go/internal/ls/converters.go:143 +0x2d9
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).ProvideDefinition(0xc010739488, {0x7ff76dfe59d0, 0xc05eecf360}, {0xc02e3db420?, 0x7ff76d5a94f0?}, {0x0?, 0x0?})
	github.com/microsoft/typescript-go/internal/ls/definition.go:17 +0xac
github.com/microsoft/typescript-go/internal/lsp.(*Server).handleDefinition(0xc0003501c0?, {0x7ff76dfe59d0?, 0xc05eecf360?}, 0xc02e3db420?, 0x65?)
	github.com/microsoft/typescript-go/internal/lsp/server.go:735 +0x35
github.com/microsoft/typescript-go/internal/lsp.init.func1.registerLanguageServiceDocumentRequestHandler[...].13({0x7ff76dfe59d0, 0xc05eecf360}, 0xc05d9571d0)
	github.com/microsoft/typescript-go/internal/lsp/server.go:518 +0x13f
github.com/microsoft/typescript-go/internal/lsp.(*Server).handleRequestOrNotification(0xc0000f4dc0, {0x7ff76dfe59d0, 0xc05eecf360}, 0xc05d9571d0)
	github.com/microsoft/typescript-go/internal/lsp/server.go:424 +0x10d
github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop.func1()
	github.com/microsoft/typescript-go/internal/lsp/server.go:329 +0x3a
created by github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop in goroutine 10
	github.com/microsoft/typescript-go/internal/lsp/server.go:349 +0x8aa

[Error - 9:42:06 AM] Request textDocument/definition failed.
  Message: InternalError: panic handling request textDocument/definition: bad line number. Line: 65, lineMap length: 33
  Code: -32603 

Steps to reproduce

I couldn't easily reproduce again. I was commenting out some code and then it appeared to error when the editor lost focus. I tried re-doing edits and it didn't occur.

The file I am in has 44 lines so not sure where bad line number 65 or line map length 33 came from.

Checking the LSP logs:

[Trace - 9:42:06 AM] Sending request 'textDocument/definition - (54)'.
Params: {
    "textDocument": {
        "uri": "file:///c%3A/Projects/a/b/c.play.ts"
    },
    "position": {
        "line": 65,
        "character": 24
    }
}


[Trace - 9:42:06 AM] Received response 'textDocument/definition - (54)' in 1ms. Request failed: InternalError: panic handling request textDocument/definition: bad line number. Line: 65, lineMap length: 33 (-32603).

so It seems it is a vscode issue - asking for a wrong line number?!

Feel free to close - I guess when this is production it will ignore errors like this instead of popping up.</issue_description>

<agent_instructions>Create a fourslash test for this issue in internal/fourslash/tests. Do not attempt to fix the issue. Only create a test that fails, reproducing the bug.</agent_instructions>

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

@iisaduan Do other files in the same folder have the same name but different extensions? @jakebailey ``` panic handling request textDocument/definition bad line number. Line: 24, lineMap length: 23 goroutine 43742 [running]: runtime/debug.Stack() runtime/debug/stack.go:26 +0x5e github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0xc00017cdc0, 0xc02ea55800) github.com/microsoft/typescript-go/internal/lsp/server.go:567 +0x58 panic({0xb147a0?, 0xc017495f00?}) runtime/panic.go:783 +0x132 github.com/microsoft/typescript-go/internal/ls.(*Converters).LineAndCharacterToPosition(0xc01695b8a8, {0xea6f90, 0xc01cfde908}, {0xf21dda8?, 0xc0?}) github.com/microsoft/typescript-go/internal/ls/converters.go:143 +0x2d9 github.com/microsoft/typescript-go/internal/ls.(*LanguageService).ProvideDefinition(0xc02d676900, {0xea88c0, 0xc01ba8a960}, {0xc01c5f6600?, 0x10000c02698b620?}, {0x0?, 0x0?}) github.com/microsoft/typescript-go/internal/ls/definition.go:17 +0xaf github.com/microsoft/typescript-go/internal/lsp.(*Server).handleDefinition(0xc00031ca20?, {0xea88c0?, 0xc01ba8a960?}, 0xc01c5f6600?, 0x53?) github.com/microsoft/typescript-go/internal/lsp/server.go:815 +0x35 github.com/microsoft/typescript-go/internal/lsp.init.func1.registerLanguageServiceDocumentRequestHandler[...].14({0xea88c0, 0xc01ba8a960}, 0xc02ea55800) github.com/microsoft/typescript-go/internal/lsp/server.go:553 +0x13f github.com/microsoft/typescri...

• Fixes Panic on textDocument/definition #1673

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