compiler: improvements for type alias handling

    
    Give an error for an attempt to define a method on an imported type.
    
    Give an error for each attempt to define a method on a builtin type.
    
    Adjust error messages to be closer to gc error messages.
    
    With these changes gccgo passes current tests on dev.typealias branch.
    
    This changes the errors printed for test/fixedbugs/issue5089.go, but
    the change is an improvement:
    
        Before:
            fixedbugs/issue5089.go:13:1: error: redefinition of ‘bufio.Buffered’: receiver name changed
             func (b *bufio.Reader) Buffered() int { // ERROR "non-local|redefinition"
             ^
            fixedbugs/issue5089.go:11:13: note: previous definition of ‘bufio.Buffered’ was here
             import "bufio" // GCCGO_ERROR "previous"
                         ^
    
        Now:
            fixedbugs/issue5089.go:13:7: error: may not define methods on non-local type
             func (b *bufio.Reader) Buffered() int { // ERROR "non-local|redefinition"
                   ^
    
    Reviewed-on: https://go-review.googlesource.com/35642

From-SVN: r244889

gcc/go/gofrontend/MERGE

-fb609ff6d940768cf4db4ab7deb93b2ab686e45d
+5c6c93f58e2aaae186bac5dcde9df1679d4896b1
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/gogo.cc

@@ -1779,18 +1779,27 @@ Gogo::start_function(const std::string& name, Function_type* type,
 
 	  while (rtype->named_type() != NULL
 		 && rtype->named_type()->is_alias())
-	    rtype = rtype->named_type()->real_type();
+	    rtype = rtype->named_type()->real_type()->forwarded();
 
 	  if (rtype->is_error_type())
 	    ret = Named_object::make_function(name, NULL, function);
 	  else if (rtype->named_type() != NULL)
 	    {
-	      ret = rtype->named_type()->add_method(name, function);
-	      if (!ret->is_function())
+	      if (rtype->named_type()->named_object()->package() != NULL)
 		{
-		  // Redefinition error.
+		  go_error_at(type->receiver()->location(),
+			      "may not define methods on non-local type");
 		  ret = Named_object::make_function(name, NULL, function);
 		}
+	      else
+		{
+		  ret = rtype->named_type()->add_method(name, function);
+		  if (!ret->is_function())
+		    {
+		      // Redefinition error.
+		      ret = Named_object::make_function(name, NULL, function);
+		    }
+		}
 	    }
 	  else if (rtype->forward_declaration_type() != NULL)
 	    {
@@ -2247,8 +2256,14 @@ Gogo::define_global_names()
 	  if (global_no->is_type())
 	    {
 	      if (no->type_declaration_value()->has_methods())
-		go_error_at(no->location(),
-			    "may not define methods for global type");
+		{
+		  for (std::vector<Named_object*>::const_iterator p =
+			 no->type_declaration_value()->methods()->begin();
+		       p != no->type_declaration_value()->methods()->end();
+		       p++)
+		    go_error_at((*p)->location(),
+				"may not define methods on non-local type");
+		}
 	      no->set_type_value(global_no->type_value());
 	    }
 	  else

gcc/testsuite/go.test/test/fixedbugs/issue5089.go

 // errorcheck
 
-// Copyright 2013 The Go Authors.  All rights reserved.
+// Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -8,7 +8,7 @@
 
 package p
 
-import "bufio"	// GCCGO_ERROR "previous"
+import "bufio"
 
 func (b *bufio.Reader) Buffered() int { // ERROR "non-local|redefinition"
 	return -1