go/types, types2: validType argument must be *Named type

Now that we have a separate top-level entry point for validType
we can use the more narrow type *Named (instead of Type) for its
argument.

Preparation for fixing issue golang#48962.

Change-Id: I93aee4abc87036c6a68323dc970efe8e617a9103
Reviewed-on: https://go-review.googlesource.com/c/go/+/379434
Trust: Robert Griesemer <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: griesemer

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

@@ -477,7 +477,9 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named
 
 	var rhs Type
 	check.later(func() {
-		check.validType(obj.typ)
+		if t, _ := obj.typ.(*Named); t != nil { // type may be invalid
+			check.validType(t)
+		}
 		// If typ is local, an error was already reported where typ is specified/defined.
 		if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
 			check.versionErrorf(tdecl.Type, "go1.18", "using type constraint %s", rhs)

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

@@ -9,7 +9,7 @@ package types2
 // defined types.
 // (Cycles involving alias types, as in "type A = [10]A" are detected
 // earlier, via the objDecl cycle detection mechanism.)
-func (check *Checker) validType(typ Type) {
+func (check *Checker) validType(typ *Named) {
 	check.validType0(typ, nil)
 }
 

src/go/types/decl.go

@@ -530,7 +530,9 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 
 	var rhs Type
 	check.later(func() {
-		check.validType(obj.typ)
+		if t, _ := obj.typ.(*Named); t != nil { // type may be invalid
+			check.validType(t)
+		}
 		// If typ is local, an error was already reported where typ is specified/defined.
 		if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
 			check.errorf(tdecl.Type, _UnsupportedFeature, "using type constraint %s requires go1.18 or later", rhs)

src/go/types/validtype.go

@@ -9,7 +9,7 @@ package types
 // defined types.
 // (Cycles involving alias types, as in "type A = [10]A" are detected
 // earlier, via the objDecl cycle detection mechanism.)
-func (check *Checker) validType(typ Type) {
+func (check *Checker) validType(typ *Named) {
 	check.validType0(typ, nil)
 }