passes/sigchanyzer: allow valid inlined unbuffered signal channel

Permit signal.Notify(make(chan os.Signal)) which is valid code,
given that the channel isn't read elsewhere, the fact that signals
can be lost is unimportant.

Updates golang/go#45043

Change-Id: Ie984dfeedbb4e1e33a29391c3abb1fc83299fed3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/311729
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

go/analysis/passes/sigchanyzer/sigchanyzer.go

@@ -49,6 +49,11 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				chanDecl = decl
 			}
 		case *ast.CallExpr:
+			// Only signal.Notify(make(chan os.Signal), os.Interrupt) is safe,
+			// conservatively treate others as not safe, see golang/go#45043
+			if isBuiltinMake(pass.TypesInfo, arg) {
+				return
+			}
 			chanDecl = arg
 		}
 		if chanDecl == nil || len(chanDecl.Args) != 1 {
@@ -127,3 +132,16 @@ func findDecl(arg *ast.Ident) ast.Node {
 	}
 	return nil
 }
+
+func isBuiltinMake(info *types.Info, call *ast.CallExpr) bool {
+	typVal := info.Types[call.Fun]
+	if !typVal.IsBuiltin() {
+		return false
+	}
+	switch fun := call.Fun.(type) {
+	case *ast.Ident:
+		return info.ObjectOf(fun).Name() == "make"
+	default:
+		return false
+	}
+}

go/analysis/passes/sigchanyzer/testdata/src/a/a.go

@@ -36,3 +36,19 @@ func j() {
 	f := signal.Notify
 	f(c, os.Interrupt) // want "misuse of unbuffered os.Signal channel as argument to signal.Notify"
 }
+
+func k() {
+	signal.Notify(make(chan os.Signal), os.Interrupt) // ok
+}
+
+func l() {
+	signal.Notify(make(chan os.Signal, 1), os.Interrupt) // ok
+}
+
+func m() {
+	signal.Notify(make(chan ao.Signal, 1), os.Interrupt) // ok
+}
+
+func n() {
+	signal.Notify(make(chan ao.Signal), os.Interrupt) // ok
+}

go/analysis/passes/sigchanyzer/testdata/src/a/a.go.golden

@@ -36,3 +36,19 @@ func j() {
 	f := signal.Notify
 	f(c, os.Interrupt) // want "misuse of unbuffered os.Signal channel as argument to signal.Notify"
 }
+
+func k() {
+	signal.Notify(make(chan os.Signal), os.Interrupt) // ok
+}
+
+func l() {
+	signal.Notify(make(chan os.Signal, 1), os.Interrupt) // ok
+}
+
+func m() {
+	signal.Notify(make(chan ao.Signal, 1), os.Interrupt) // ok
+}
+
+func n() {
+	signal.Notify(make(chan ao.Signal), os.Interrupt) // ok
+}