Don't incorrectly parse expression as type switch.

Improve error reporting of invalid type assertions.

From-SVN: r167787

gcc/go/gofrontend/expressions.cc

@@ -11620,24 +11620,29 @@ Type_guard_expression::do_check_types(Gogo*)
 	this->report_error(_("invalid unsafe.Pointer conversion"));
     }
   else if (expr_type->interface_type() == NULL)
+    {
+      if (!expr_type->is_error_type() && !this->type_->is_error_type())
 	this->report_error(_("type assertion only valid for interface types"));
+      this->set_is_error();
+    }
   else if (this->type_->interface_type() == NULL)
     {
       std::string reason;
       if (!expr_type->interface_type()->implements_interface(this->type_,
 							     &reason))
 	{
+	  if (!this->type_->is_error_type())
+	    {
 	      if (reason.empty())
 		this->report_error(_("impossible type assertion: "
 				     "type does not implement interface"));
 	      else
-	    {
 		error_at(this->location(),
 			 ("impossible type assertion: "
 			  "type does not implement interface (%s)"),
 			 reason.c_str());
-	      this->set_is_error();
 	    }
+	  this->set_is_error();
 	}
     }
 }

gcc/go/gofrontend/parse.cc

@@ -2647,12 +2647,18 @@ Parse::selector(Expression* left, bool* is_type_switch)
     {
       this->advance_token();
       Type* type = NULL;
-      if (is_type_switch == NULL
-	  || !this->peek_token()->is_keyword(KEYWORD_TYPE))
+      if (!this->peek_token()->is_keyword(KEYWORD_TYPE))
 	type = this->type();
       else
 	{
+	  if (is_type_switch != NULL)
 	    *is_type_switch = true;
+	  else
+	    {
+	      error_at(this->location(),
+		       "use of %<.(type)%> outside type switch");
+	      type = Type::make_error_type();
+	    }
 	  this->advance_token();
 	}
       if (!this->peek_token()->is_op(OPERATOR_RPAREN))
@@ -2866,7 +2872,7 @@ Parse::expression(Precedence precedence, bool may_be_sink,
       left = this->verify_not_sink(left);
       Expression* right = this->expression(right_precedence, false,
 					   may_be_composite_lit,
-					   is_type_switch);
+					   NULL);
       if (op == OPERATOR_CHANOP)
 	left = Expression::make_send(left, right, binop_location);
       else
@@ -2959,8 +2965,7 @@ Parse::unary_expr(bool may_be_sink, bool may_be_composite_lit,
 	  return Expression::make_type(this->type(), location);
 	}
 
-      Expression* expr = this->unary_expr(false, may_be_composite_lit,
-					  is_type_switch);
+      Expression* expr = this->unary_expr(false, may_be_composite_lit, NULL);
       if (expr->is_error_expression())
 	;
       else if (op == OPERATOR_MULT && expr->is_type_expression())

gcc/go/gofrontend/statements.cc

@@ -1296,6 +1296,7 @@ Tuple_type_guard_assignment_statement::do_lower(Gogo*, Block* enclosing)
   Type* expr_type = this->expr_->type();
   if (expr_type->interface_type() == NULL)
     {
+      if (!expr_type->is_error_type() && !this->type_->is_error_type())
 	this->report_error(_("type assertion only valid for interface types"));
       return Statement::make_error_statement(loc);
     }