nilctxpassed isBuiltinNil still lacks ParenExpr unwrap (issue 63343 auto-expired, 3rd occurrence) #65227

Lineage: #61519 (filed R69) -> #63343 (R77 refile, auto-expired closed/not_planned on 2026-10-02) -> this issue (R85 refile). Third time this exact bug has been filed with zero code change in between.

Bug

isBuiltinNil (pkg/linters/nilctxpassed/nilctxpassed.go:124-135) performs a bare type assertion with no ParenExpr unwrap first:

func isBuiltinNil(pass *analysis.Pass, expr ast.Expr) bool {
	ident, ok := expr.(*ast.Ident)
	if !ok || ident.Name != "nil" {
		return false
	}
	...
}

A parenthesized nil literal passed as a context.Context argument, e.g. doSomething((nil)), is legal (if unusual) Go and is completely invisible to this linter since (nil) is an *ast.ParenExpr, not an *ast.Ident, and the assertion fails before TypesInfo is ever consulted.

Re-verified 2026-10-03: nilctxpassed.go:124-135 unchanged; zero occurrences of UnwrapParenExpr anywhere in the file.

CI enforcement: .github/workflows/cgo.yml LINTER_FLAGS include -nilctxpassed on both the native and wasm custom-linter steps with -test=false.

Live impact: no production false negative found (grepped for parenthesized nil-literal arguments in context-typed call positions across pkg/, none found) -- latent but genuinely untested, zero ParenExpr coverage in testdata.

Pattern class: paren_unwrap_gap -- the same recurring class already fixed via astutil.UnwrapParenExpr in walkfuncerrshadow.go, mapdeletecheck.go, and packagelevelmutableslicemap.go, and via astutil.TwoValueTypeAssertionOKIdent in typeassertionokdiscarded.go.

Recommendation

Wrap expr with astutil.UnwrapParenExpr(expr) before the *ast.Ident assertion in isBuiltinNil, matching the established fix idiom used elsewhere in this codebase.

Validation checklist

• Add a testdata case doSomething((nil)) (parenthesized nil as a context.Context argument) expecting a diagnostic
• Confirm existing non-paren nil and non-nil testdata cases are unaffected

Effort: trivial -- one-line unwrap plus one testdata case.

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• expires on Oct 9, 2026, 8:11 PM UTC-08:00