fix: parenthesized expression as receiver (#78)

Fixes #77.

check/check.go

@@ -913,6 +913,8 @@ func recvPrefix(recv *ast.FieldList) string {
 		return expr.Name + "."
 	case *ast.IndexExpr:
 		return expr.X.(*ast.Ident).Name + "."
+	case *ast.ParenExpr:
+		return expr.X.(*ast.Ident).Name + "."
 	case *ast.IndexListExpr:
 		return expr.X.(*ast.Ident).Name + "."
 	default:

testdata/script/parenthesized_expression.txtar

@@ -0,0 +1,20 @@
+! exec unparam .
+cmp stdout stdout.golden
+
+-- go.mod --
+module testdata.tld/foo
+
+go 1.18
+-- stdout.golden --
+foo.go:7:37: (*FooType).multImplsMethod - a is unused
+-- foo.go --
+package foo
+
+var DoWork func()
+
+type FooType int
+
+func (f *(FooType)) multImplsMethod(a int) int64 {
+	DoWork()
+	return 3
+}