go/types, types2: don't register interface methods in Info.Types map

Methods declared in an interface have a signature and FuncType in the
AST, but they do not express a syntactic function type expression.
Treat them like ordinary function/method declarations and do not record
them in the Info.Types map. This removes an inconsistency in the way
function types are recorded.

Follow-up on CL 640776.

For #70908.

Change-Id: I60848f209b40b008039c014fb8b7b279361487b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/640596
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

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

@@ -137,17 +137,19 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 		name := f.Name.Value
 		if name == "_" {
 			check.error(f.Name, BlankIfaceMethod, "methods must have a unique non-blank name")
-			continue // ignore
+			continue // ignore method
 		}
 
-		typ := check.typ(f.Type)
-		sig, _ := typ.(*Signature)
-		if sig == nil {
-			if isValid(typ) {
-				check.errorf(f.Type, InvalidSyntaxTree, "%s is not a method signature", typ)
-			}
-			continue // ignore
+		// Type-check method declaration.
+		// Note: Don't call check.typ(f.Type) as that would record
+		// the method incorrectly as a type expression in Info.Types.
+		ftyp, _ := f.Type.(*syntax.FuncType)
+		if ftyp == nil {
+			check.errorf(f.Type, InvalidSyntaxTree, "%s is not a method signature", f.Type)
+			continue // ignore method
 		}
+		sig := new(Signature)
+		check.funcType(sig, nil, nil, ftyp)
 
 		// use named receiver type if available (for better error messages)
 		var recvTyp Type = ityp

src/go/types/interface.go

@@ -176,17 +176,19 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 		name := f.Names[0]
 		if name.Name == "_" {
 			check.error(name, BlankIfaceMethod, "methods must have a unique non-blank name")
-			continue // ignore
+			continue // ignore method
 		}
 
-		typ := check.typ(f.Type)
-		sig, _ := typ.(*Signature)
-		if sig == nil {
-			if isValid(typ) {
-				check.errorf(f.Type, InvalidSyntaxTree, "%s is not a method signature", typ)
-			}
-			continue // ignore
+		// Type-check method declaration.
+		// Note: Don't call check.typ(f.Type) as that would record
+		// the method incorrectly as a type expression in Info.Types.
+		ftyp, _ := f.Type.(*ast.FuncType)
+		if ftyp == nil {
+			check.errorf(f.Type, InvalidSyntaxTree, "%s is not a method signature", f.Type)
+			continue // ignore method
 		}
+		sig := new(Signature)
+		check.funcType(sig, nil, ftyp)
 
 		// The go/parser doesn't accept method type parameters but an ast.FuncType may have them.
 		if sig.tparams != nil {