Fix nil pointer dereference in completion at property start after JSDoc

[Copilot]

Requesting completions at the beginning of a property name preceded by JSDoc caused a nil pointer panic when accessing contextToken.Kind.

Root Causes

1. Variable shadowing in getRelevantTokens: Used := instead of =, creating a local variable that shadowed the return parameter, causing contextToken to return nil.

2. Missing nil check in tryGetObjectTypeDeclarationCompletionContainer: The function could return a non-nil declaration even when contextToken was nil (specifically in the KindIdentifier case when isFromObjectTypeDeclaration(location) is true), leading to a crash when the caller tried to access contextToken.Kind.

Changes

• Fixed variable shadowing in getRelevantTokens (line 2756) by changing contextToken := to contextToken = to properly assign to the return parameter
• Added nil check in tryGetObjectTypeDeclarationCompletionContainer (line 4166) by adding contextToken != nil && condition before isFromObjectTypeDeclaration(location)
• Added test TestCompletionJSDocBeforePropertyNoCrash to verify the crash is fixed

// Before: shadows the return parameter
contextToken := astnav.FindPrecedingToken(file, previousToken.Pos())

// After: assigns to return parameter
contextToken = astnav.FindPrecedingToken(file, previousToken.Pos())

// Before: could return declaration when contextToken is nil
if isFromObjectTypeDeclaration(location) {
    return ast.FindAncestor(location, ast.IsObjectTypeDeclaration)
}

// After: prevents returning declaration when contextToken is nil
if contextToken != nil && isFromObjectTypeDeclaration(location) {
    return ast.FindAncestor(location, ast.IsObjectTypeDeclaration)
}

Testing

• ✅ Added test that reproduces the original crash scenario
• ✅ All completion tests pass (25+ tests)
• ✅ All fourslash tests pass (100+ tests)

The fixes ensure contextToken is correctly set and prevent accessing it when nil, resolving the crash while maintaining correct completion behavior.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Crash completing beginning of property name when preceded by JSDoc</issue_title> <issue_description>```ts export class SomeInterface { /** ruh-roh! / /$1*/property: string; }

export class SomeClass { /** ruh-roh! / /$2*/property = "value"; }

Request completions at the beginning of either property (markers `/*$1*/` and `/*$2*/`).

error] panic handling requesttextDocument/completionruntime error: invalid memory address or nil pointer dereferencegoroutine 23769 [running]: runtime/debug.Stack() runtime/debug/stack.go:26 +0x5e github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0xc0001e4008, 0xc026483a10) github.com/microsoft/typescript-go/internal/lsp/server.go:872 +0x58 panic({0xbddea0?, 0x16c8b70?}) runtime/panic.go:783 +0x132 github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getCompletionData.func15() github.com/microsoft/typescript-go/internal/ls/completions.go:1447 +0xba github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getCompletionData.func18(...) github.com/microsoft/typescript-go/internal/ls/completions.go:1689 github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getCompletionData(0xc029141380, {0x107d088, 0xc029141320}, 0xc036d90008, 0xc005362f08, 0x85, 0xc0097e1e00) github.com/microsoft/typescript-go/internal/ls/completions.go:1717 +0x1edf github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getCompletionsAtPosition(0xc029141380, {0x107d088, 0xc029141320}, 0xc005362f08, 0x85, 0x0) github.com/microsoft/typescript-go/internal/ls/completions.go:383 +0x2cf github.com/microsoft/typescript-go/internal/ls.(*LanguageService).ProvideCompletion(0xc029141380, {0x107d088, 0xc029141320}, {0xc0035e8690?, 0xc029141320?}, {0x35e8690?, 0xc0?}, 0xc02b74b0f0) github.com/microsoft/typescript-go/internal/ls/completions.go:44 +0xc8 github.com/microsoft/typescript-go/internal/lsp.(*Server).handleCompletion(0xc00140c008?, {0x107d088?, 0xc029141320?}, 0xc0035e8690?, 0x40b92c?) github.com/microsoft/typescript-go/internal/lsp/server.go:1208 +0x39 github.com/microsoft/typescript-go/internal/lsp.init.func1.registerLanguageServiceDocumentRequestHandler[...].16({0x107d088, 0xc029141320}, 0xc026483a10) github.com/microsoft/typescript-go/internal/lsp/server.go:621 +0x130 github.com/microsoft/typescript-go/internal/lsp.(*Server).handleRequestOrNotification(0xc0001e4008, {0x107d0c0?, 0xc01d1484b0?}, 0xc026483a10) github.com/microsoft/typescript-go/internal/lsp/server.go:502 +0x14b github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop.func1() github.com/microsoft/typescript-go/internal/lsp/server.go:405 +0x3a created by github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop in goroutine 10 github.com/microsoft/typescript-go/internal/lsp/server.go:425 +0x9ad

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

<comments>
</comments>

• Fixes microsoft/typescript-go#2253

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.