go/types, types2: constraints may be parenthesized and that includes …

…"any"

Change-Id: I9a234cc1f04ca762375b51ec8ef009fb264c7ed1
Reviewed-on: https://go-review.googlesource.com/c/go/+/295689
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/decl.go

@@ -707,7 +707,7 @@ func (check *Checker) collectTypeParams(list []*syntax.Field) (tparams []*TypeNa
 		// The predeclared identifier "any" is visible only as a constraint
 		// in a type parameter list. Look for it before general constraint
 		// resolution.
-		if tident, _ := f.Type.(*syntax.Name); tident != nil && tident.Value == "any" && check.lookup("any") == nil {
+		if tident, _ := unparen(f.Type).(*syntax.Name); tident != nil && tident.Value == "any" && check.lookup("any") == nil {
 			bound = universeAny
 		} else {
 			bound = check.typ(f.Type)

src/cmd/compile/internal/types2/testdata/typeparams.go2

@@ -19,6 +19,10 @@ func _[_ any](x int) int
 func _[T any](T /* ERROR redeclared */ T)()
 func _[T, T /* ERROR redeclared */ any]()
 
+// Constraints (incl. any) may be parenthesized.
+func _[_ (any)]() {}
+func _[_ (interface{})]() {}
+
 func reverse[T any](list []T) []T {
         rlist := make([]T, len(list))
         i := len(list)

src/go/types/decl.go

@@ -726,7 +726,7 @@ func (check *Checker) collectTypeParams(list *ast.FieldList) (tparams []*TypeNam
 		// The predeclared identifier "any" is visible only as a constraint
 		// in a type parameter list. Look for it before general constraint
 		// resolution.
-		if tident, _ := f.Type.(*ast.Ident); tident != nil && tident.Name == "any" && check.lookup("any") == nil {
+		if tident, _ := unparen(f.Type).(*ast.Ident); tident != nil && tident.Name == "any" && check.lookup("any") == nil {
 			bound = universeAny
 		} else {
 			bound = check.typ(f.Type)

src/go/types/testdata/typeparams.go2

@@ -19,6 +19,10 @@ func _[_ any](x int) int
 func _[T any](T /* ERROR redeclared */ T)()
 func _[T, T /* ERROR redeclared */ any]()
 
+// Constraints (incl. any) may be parenthesized.
+func _[_ (any)]() {}
+func _[_ (interface{})]() {}
+
 func reverse[T any](list []T) []T {
         rlist := make([]T, len(list))
         i := len(list)