Fix panic on negative indentation in JSDoc formatting within nested scopes

[Copilot]

The formatter panics with "strings: negative Repeat count" when formatting JSDoc comments inside callback functions. The code uses -1 as a sentinel for "no indentation computed", which propagates to strings.Repeat() in certain nested scopes.

Reproduces with:

document.addEventListener('DOMContentLoaded', () => {
    /** @type {NodeListOf<HTMLSpanElement>} */
    const elements = document.querySelectorAll('.test')
});

Changes:

• Add negative indentation guards in getIndentationString, insertIndentation, and indentMultilineComment
• Return empty string / skip formatting when indentation is negative
• Add regression test TestFormatJSDocInNestedScope

The sentinel value now short-circuits formatting instead of causing a panic.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>LSP Panic: strings: negative Repeat count when formatting JSDoc within nested scope</issue_title>
<issue_description>The LSP server crashes (panics) when attempting to format a JavaScript/TypeScript file containing a JSDoc @type annotation inside a callback function.

Stack trace

[ERROR][2026-02-03 12:29:18] ...lsp/handlers.lua:562	"panic handling request textDocument/formatting: strings: negative Repeat count
goroutine 204 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:26 +0x5e
github.com/microsoft/typescript-go/internal/lsp.(*Server).recover(0xc000232708, {0x441ae5?, 0xc0007aafc0?}, 0xc003402660)
	github.com/microsoft/typescript-go/internal/lsp/server.go:780 +0x4c
panic({0xc01ae0?, 0x10ffd40?})
	runtime/panic.go:783 +0x132
strings.Repeat({0x10fc098?, 0xc0002c9034?}, 0xc0033d1c40?)
	strings/strings.go:628 +0x585
github.com/microsoft/typescript-go/internal/format.getIndentationString(0xffffffffffffffff, 0xc001cfe000?)
	github.com/microsoft/typescript-go/internal/format/span.go:980 +0x7f
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).insertIndentation(0xc0003f8690, 0x38, 0xffffffffffffffff, 0x0)
	github.com/microsoft/typescript-go/internal/format/span.go:863 +0x45
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).indentMultilineComment(0xc0003f8690, {0x0?, 0x0?}, 0xffffffffffffffff, 0x0, 0x1)
	github.com/microsoft/typescript-go/internal/format/span.go:922 +0x185
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).indentTriviaItems(0xc0003f8690, {0xc0003a9560?, 0x62?, 0xc000145700?}, 0xffffffffffffffff, 0xc8?, 0xc0033d1ed0)
	github.com/microsoft/typescript-go/internal/format/span.go:899 +0xcb
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).consumeTokenAndAdvanceScanner(0xc0003f8690, {{0xc0003a9560, 0x4, 0x4}, {{0x65, 0x6a}, 0x56}, {0xc0033c3060, 0x1, 0x1}}, ...)
	github.com/microsoft/typescript-go/internal/format/span.go:1062 +0x3cc
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).processChildNodes(0xc0003f8690, 0xc000145700, 0xc00338d9e0, 0x2, 0x2, 0xc000145680, 0xc000145700, 0x2, 0xc00338d9e0)
	github.com/microsoft/typescript-go/internal/format/span.go:483 +0x905
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).execute.func2(0xc000145680, 0x30?)
	github.com/microsoft/typescript-go/internal/format/span.go:238 +0x4c
github.com/microsoft/typescript-go/internal/ast.(*NodeVisitor).visitNodes(0xc0033d20d0?, 0x477705?)
	github.com/microsoft/typescript-go/internal/ast/visitor.go:234 +0x25
github.com/microsoft/typescript-go/internal/ast.(*VariableDeclarationList).VisitEachChild(0xc000145700, 0xc0023926c0)
	github.com/microsoft/typescript-go/internal/ast/ast.go:3840 +0x27
github.com/microsoft/typescript-go/internal/ast.(*Node).VisitEachChild(...)
	github.com/microsoft/typescript-go/internal/ast/ast.go:246
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).executeProcessNodeVisitor(0xc0003f8690, 0x1?, 0xc0020daa80?, 0xc0033c2e30?, 0xc0003a9560?)
	github.com/microsoft/typescript-go/internal/format/span.go:527 +0xb0
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).processNode(0xc0003f8690, 0xc000145700, 0xc0001c8cc8, 0x2, 0x2, 0xffffffffffffffff, 0x8)
	github.com/microsoft/typescript-go/internal/format/span.go:624 +0x15d
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).processChildNode(0xc0003f8690, 0xc00010bb80, 0xc0033d2390?, 0x6765ab?, 0xc0001c8e08?, 0xc000145700, 0xffffffffffffffff, 0xc00010bb80, 0xc00338d9b0, 0x2, ...)
	github.com/microsoft/typescript-go/internal/format/span.go:417 +0x7e5
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).execute.func1(0xc000145700)
	github.com/microsoft/typescript-go/internal/format/span.go:231 +0x65
github.com/microsoft/typescript-go/internal/ast.(*NodeVisitor).VisitNode(0x5000000000065?, 0x779b29624948?)
	github.com/microsoft/typescript-go/internal/ast/visitor.go:51 +0x27
github.com/microsoft/typescript-go/internal/ast.(*NodeVisitor).visitNode(0xc0001ee008?, 0xc00338d9b0?)
	github.com/microsoft/typescript-go/internal/ast/visitor.go:198 +0x30
github.com/microsoft/typescript-go/internal/ast.(*VariableStatement).VisitEachChild(0xc00010bb80, 0xc0023926c0)
	github.com/microsoft/typescript-go/internal/ast/ast.go:3736 +0x3f
github.com/microsoft/typescript-go/internal/ast.(*Node).VisitEachChild(...)
	github.com/microsoft/typescript-go/internal/ast/ast.go:246
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).executeProcessNodeVisitor(0xc0003f8690, 0xc000022f90?, 0xc0002c906b?, 0xa?, 0xc0003a9560?)
	github.com/microsoft/typescript-go/internal/format/span.go:527 +0xb0
github.com/microsoft/typescript-go/internal/format.(*formatSpanWorker).processNode(0xc0003f8690, 0xc00010bb80, 0xc0001c8cc8, 0x2, 0x2, 0xffffffffffffffff, 0x8)
	github.com/microsoft/typesc...

</details>



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- Fixes microsoft/typescript-go#2649

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