go/types: avoid follow-up error if composite literal type is unknown

Fixes #9182.

Change-Id: I7090e600e9981131db7f323e7ce6419017e95458
Reviewed-on: https://go-review.googlesource.com/2481
Reviewed-by: Alan Donovan <adonovan@google.com>

go/types/expr.go

@@ -1126,9 +1126,12 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 			}
 
 		default:
+			// if utyp is invalid, an error was reported before
+			if utyp != Typ[Invalid] {
 				check.errorf(e.Pos(), "invalid composite literal type %s", typ)
 				goto Error
 			}
+		}
 
 		x.mode = value
 		x.typ = typ

go/types/testdata/issues.src

@@ -35,3 +35,9 @@ func issue8799b(x int, ok bool) {
 	_ = !ok
 	_ = x
 }
+
+func issue9182() {
+	type Point C /* ERROR undeclared */ .Point
+	// no error for composite literal based on unknown type
+	_ = Point{x: 1, y: 2}
+}