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Anonymous-function analysis panics on a variadic function literal that captures a pointer-typed variable #532
Description
-experimental-anonymous-function panics on a variadic function literal that captures a pointer-typed variable.
Version: go.uber.org/nilaway v0.0.0-20260918162853-acb8859b9031, Go 1.27.2 (darwin/arm64), golang.org/x/tools v0.50.0.
Reproducer (module example.com/repro, package b):
package b
type App struct{ Home string }
func (a *App) Roots() []string {
join := func(parts ...string) string { return a.Home + parts[0] }
return []string{join("x")}
}$ nilaway -experimental-anonymous-function -include-errors-in-files=/ ./...
b/b.go:1:1: error: INTERNAL ERROR(s):
nilaway_assertion_analyzer: nilaway_function_analyzer: INTERNAL PANIC from "nilaway_anonymous_func_analyzer": got *example.com/repro/b.App, want variadic parameter of slice or string type
(-include-errors-in-files=/ is only there so the diagnostic is not filtered, #533.)
A literal that captures only a string does not panic, so the trigger is a variadic literal that captures a variable NilAway tracks (here the *App receiver). This is a common idiom (h := func(parts ...string) string { ... receiver ... }).
Cause: createFakeFuncDecl (assertion/anonymousfunc/analyzer.go) appends the captured variables after the literal's own parameters but still passes sig.Variadic() to types.NewSignatureType. The last parameter is then a captured variable, not a slice, so NewSignatureType panics. Passing variadic=false for the fake signature when there are captured variables, or inserting them before the variadic parameter, would probably avoid it.
As with #531, the panic discards the package's other findings: a genuine nil dereference in the same package is no longer reported once the flag is on.
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