Fix nil pointer dereference in range formatting

[Copilot]

Fix crash in range formatting when requested on a line different from containing function

• Fix nil pointer dereference in getIndentationForNodeWorker at indent.go:69
• Add test case to reproduce the crash scenario
• Run existing tests to ensure no regressions
• Verify fix handles edge cases properly
• Code review completed - no issues found
• Security check passed
• Refactored based on code review feedback

Summary

Fixed a nil pointer dereference that caused a panic during range formatting when the containing list had no children. The fix adds a nil check before calling getStartLineAndCharacterForNode to prevent accessing a nil node's position.

Changes Made

1. internal/format/indent.go: Added nil check and refactored to compute listIndentsChild directly within the check, avoiding redundant nil checks
2. internal/ls/format_test.go: Added comprehensive test cases covering multiple edge cases from the issue

All tests pass successfully.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Crash in range formatting when requested on a line that is different from the containing function</issue_title>
<issue_description>```
function foo() {
[|return (1 + 2);|]
}

Format the range (trigger with <kbd>Ctrl</kbd>+<kbd>K</kbd>; <kbd>Ctrl</kbd>+<kbd>F</kbd>).

panic handling request textDocument/rangeFormatting runtime error: invalid memory address or nil pointer dereference goroutine 2169 [running]:
runtime/debug.Stack()
runtime/debug/stack.go:26 +0x64
github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0x4000000f00, 0x400c378180)
github.com/microsoft/typescript-go/internal/lsp/server.go:567 +0x44
panic({0x7ff78a61ad20?, 0x7ff78af56550?})
runtime/panic.go:783 +0x120
github.com/microsoft/typescript-go/internal/ast.(*Node).Pos(...)
github.com/microsoft/typescript-go/internal/ast/ast.go:240
github.com/microsoft/typescript-go/internal/scanner.GetTokenPosOfNode(0xf?, 0x29?, 0xc0?)
github.com/microsoft/typescript-go/internal/scanner/scanner.go:2323 +0xa8
github.com/microsoft/typescript-go/internal/format.getStartLineAndCharacterForNode(0x400c2b46c0?, 0x40060cbb08)
github.com/microsoft/typescript-go/internal/format/indent.go:250 +0x24
github.com/microsoft/typescript-go/internal/format.getIndentationForNodeWorker(0x7ff78a97b790?, 0x40060cbb08?, 0xf?, 0x4006151d48, 0x7ff78a97d0e8?, 0x40060cbb08, 0x0, 0x40034ea150)
github.com/microsoft/typescript-go/internal/format/indent.go:69 +0x154
github.com/microsoft/typescript-go/internal/format.GetIndentationForNode(0x400c2b46c0, 0x4006151d48, 0x40060cbb08, 0x40034ea150)
github.com/microsoft/typescript-go/internal/format/indent.go:17 +0x6c
github.com/microsoft/typescript-go/internal/format.FormatSpan({0x7ff78a97d0e8, 0x400ac40180}, {0x12, 0x26}, 0x40060cbb08, 0x1)
github.com/microsoft/typescript-go/internal/format/api.go:69 +0xbc
github.com/microsoft/typescript-go/internal/format.FormatSelection({0x7ff78a97d0e8, 0x400ac40180}, 0x40060cbb08, 0x7ff78a970f20?, 0x26)
github.com/microsoft/typescript-go/internal/format/api.go:112 +0x50
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getFormattingEditsForRange(0x400a301470?, {0x7ff78a97d120?, 0x4009878000?}, 0x40060cbb08, 0x17?, {0x0?, 0x0?})
github.com/microsoft/typescript-go/internal/ls/format.go:95 +0x5c
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).ProvideFormatDocumentRange(0x400ac400f0, {0x7ff78a97d120, 0x4009878000}, {0x4009ba8300?, 0x4006151e78?}, 0x400ac1a000, {{0x46bcb97d?, 0x12?}, {0x634352ec?, 0x1395cb5?}})
github.com/microsoft/typescript-go/internal/ls/format.go:61 +0xf8
github.com/microsoft/typescript-go/internal/lsp.(*Server).handleDocumentRangeFormat(0x40002a0a20?, {0x7ff78a97d120?, 0x4009878000?}, 0x4009ba8300?, 0x13?)
github.com/microsoft/typescript-go/internal/lsp/server.go:869 +0x40
github.com/microsoft/typescript-go/internal/lsp.init.func1.registerLanguageServiceDocumentRequestHandler[...].21({0x7ff78a97d120, 0x4009878000}, 0x400c378180)
github.com/microsoft/typescript-go/internal/lsp/server.go:553 +0xe0
github.com/microsoft/typescript-go/internal/lsp.(*Server).handleRequestOrNotification(0x4000000f00, {0x7ff78a97d120, 0x4009878000}, 0x400c378180)
github.com/microsoft/typescript-go/internal/lsp/server.go:449 +0xf4
github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop.func1()
github.com/microsoft/typescript-go/internal/lsp/server.go:354 +0x34
created by github.com/microsoft/typescript-go/internal/lsp.(*Server).dispatchLoop in goroutine 10
github.com/microsoft/typescript-go/internal/lsp/server.go:374 +0x79c

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

<comments>
<comment_new><author>@DanielRosenwasser</author><body>
Updated title - I think you can trigger this just by requesting formatting ranges anywhere after the first line of the function

```ts
function
/*$*/f() {
}

function f() {
  /*$*/
}

function f() {
}/*$*/

[Error - 11:14:49 AM] Request textDocument/rangeFormatting failed.
  Message: InternalError: panic handling request textDocument/rangeFormatting: runtime error: invalid memory address or nil pointer dereference
  Code: -32603 
panic handling request textDocument/rangeFormatting runtime error: invalid memory address or nil pointer dereference goroutine 1294 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:26 +0x64
github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0x4000000f00, 0x40089fb8c0)
	github.com/microsoft/typescript-go/internal/lsp/server.go:570 +0x44
panic({0x7ff71019e300?, 0x7ff710add530?})
	runtime/panic.go:783 +0x120
github.com/microsoft/typescript-go/internal/ast.(*Node).Pos(...)
	github.com/microsoft/typescript-go/internal/ast/ast.go:240
github.com/microsoft/typescript-go/internal/scanner.GetTokenPosOfNode(0xe?, 0x12?, 0x20?)
	github.com/microsoft/typescript-go/internal/scanner/scanner.go:2323 +0xa8
github...

</details>

- Fixes microsoft/typescript-go#1992

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[jakebailey]

@copilot Seems right, since the old code said:

const listIndentsChild = !!firstListChild && getStartLineAndCharacterForNode(firstListChild, sourceFile).line > containingListOrParentStart.line;

But, this would be better written more like:

var listIndentsChild bool
if firstListChild != nil {
	listLine, _ := getStartLineAndCharacterForNode(firstListChild, sourceFile)
	listIndentsChild = listLine > containingListOrParentStartLine
}

[Copilot]

Updated in 76969b2 - moved the logic inside the nil check to avoid the redundant check and limit variable scope.