go/types: fix error message for embedded non-interface types in inter…

…faces

Fixes golang#10979.

Change-Id: Iac25645ba8181a56a75ddfcd29ff6d64c15c4f57
Reviewed-on: https://go-review.googlesource.com/10466
Reviewed-by: Alan Donovan <[email protected]>

src/go/types/testdata/issues.src

@@ -71,3 +71,27 @@ func issue9473(a []int, b ...int) {
  append_(f0(), f1()... /* ERROR cannot use */ )
  append_(f0(), f2()... /* ERROR cannot use */ )
 }
+
+// Check that embedding a non-interface type in an interface results in a good error message.
+func issue10979() {
+ type _ interface {
+ int /* ERROR int is not an interface */
+ }
+ type T struct{}
+ type _ interface {
+ T /* ERROR T is not an interface */
+ }
+ type _ interface {
+ nosuchtype /* ERROR undeclared name: nosuchtype */
+ }
+ type _ interface {
+ fmt /* ERROR Nosuchtype not declared by package fmt */ .Nosuchtype
+ }
+ type _ interface {
+ nosuchpkg /* ERROR undeclared name: nosuchpkg */ .Nosuchtype
+ }
+ type I interface {
+ I /* ERROR I\.m \(value of type func\(I\)\) is not a type */ .m
+ m()
+ }
+}

src/go/types/typexpr.go

@@ -525,20 +525,14 @@ func (check *Checker) interfaceType(iface *Interface, ityp *ast.InterfaceType, d
  for _, e := range embedded {
  pos := e.Pos()
  typ := check.typExpr(e, nil, path)
+ // Determine underlying embedded (possibly incomplete) type
+ // by following its forward chain.
  named, _ := typ.(*Named)
- if named == nil {
- if typ != Typ[Invalid] {
- check.invalidAST(pos, "%s is not named type", typ)
- }
- continue
- }
- // determine underlying (possibly incomplete) type
- // by following its forward chain
- u := underlying(named)
- embed, _ := u.(*Interface)
+ under := underlying(named)
+ embed, _ := under.(*Interface)
  if embed == nil {
- if u != Typ[Invalid] {
- check.errorf(pos, "%s is not an interface", named)
+ if typ != Typ[Invalid] {
+ check.errorf(pos, "%s is not an interface", typ)
  }
  continue
  }