Go patch committed: treat map index expressions as lvalues in range expressions

[Ian Lance Taylor]

This patch by Chris Manghane fixes a bug in the gofrontend in which
map index expressions were not treated as lvalues in range
expressions.  That is,
    for m[0] = range s
did not work.  This was Go issue 9695.  Bootstrapped and ran Go
testsuite on x86_64-unknown-linux-gnu.  Committed to mainline.

Ian

diff -r 172f17c15975 go/parse.cc
--- a/go/parse.cc       Fri Jan 30 08:04:31 2015 -0800
+++ b/go/parse.cc       Fri Jan 30 16:17:50 2015 -0800
@@ -4011,36 +4011,8 @@
 
   token = this->advance_token();
 
-  if (p_range_clause != NULL && token->is_keyword(KEYWORD_RANGE))
-    {
-      if (op != OPERATOR_EQ)
-       error_at(this->location(), "range clause requires %<=%>");
-      this->range_clause_expr(lhs, p_range_clause);
-      return;
-    }
-
-  Expression_list* vals = this->expression_list(NULL, false,
-                                               may_be_composite_lit);
-
-  // We've parsed everything; check for errors.
-  if (lhs == NULL || vals == NULL)
+  if (lhs == NULL)
     return;
-  for (Expression_list::const_iterator pe = lhs->begin();
-       pe != lhs->end();
-       ++pe)
-    {
-      if ((*pe)->is_error_expression())
-       return;
-      if (op != OPERATOR_EQ && (*pe)->is_sink_expression())
-       error_at((*pe)->location(), "cannot use _ as value");
-    }
-  for (Expression_list::const_iterator pe = vals->begin();
-       pe != vals->end();
-       ++pe)
-    {
-      if ((*pe)->is_error_expression())
-       return;
-    }
 
   // Map expressions act differently when they are lvalues.
   for (Expression_list::iterator plv = lhs->begin();
@@ -4049,6 +4021,37 @@
     if ((*plv)->index_expression() != NULL)
       (*plv)->index_expression()->set_is_lvalue();
 
+  if (p_range_clause != NULL && token->is_keyword(KEYWORD_RANGE))
+    {
+      if (op != OPERATOR_EQ)
+       error_at(this->location(), "range clause requires %<=%>");
+      this->range_clause_expr(lhs, p_range_clause);
+      return;
+    }
+
+  Expression_list* vals = this->expression_list(NULL, false,
+                                               may_be_composite_lit);
+
+  // We've parsed everything; check for errors.
+  if (vals == NULL)
+    return;
+  for (Expression_list::const_iterator pe = lhs->begin();
+       pe != lhs->end();
+       ++pe)
+    {
+      if ((*pe)->is_error_expression())
+       return;
+      if (op != OPERATOR_EQ && (*pe)->is_sink_expression())
+       error_at((*pe)->location(), "cannot use _ as value");
+    }
+  for (Expression_list::const_iterator pe = vals->begin();
+       pe != vals->end();
+       ++pe)
+    {
+      if ((*pe)->is_error_expression())
+       return;
+    }
+
   Call_expression* call;
   Index_expression* map_index;
   Receive_expression* receive;