c++, contracts: Improve postcondition locations.

We should now point to the postcondition var if relevant:

    3 |   post (r: r > 5)
      |   ~~~~~~^~~~~~~~~

We now apply a wrapper when deferring parses - so that the identifier can
be re-created in the actual parse.  We also check for this in the relevant
places.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

Author: iains

gcc/cp/contracts.cc

@@ -2849,17 +2849,24 @@ start_function_contracts (tree fndecl)
       if (POSTCONDITION_P (CONTRACT_STATEMENT (ca)))
 	if (tree id = POSTCONDITION_IDENTIFIER (CONTRACT_STATEMENT (ca)))
 	  {
+	    tree r_name = tree_strip_any_location_wrapper (id);
 	    if (TREE_CODE (id) == PARM_DECL)
-	      id = DECL_NAME (id);
-	    gcc_checking_assert (id && TREE_CODE (id) == IDENTIFIER_NODE);
-	    tree seen = lookup_name (id);
+	      r_name = DECL_NAME (id);
+	    gcc_checking_assert (r_name && TREE_CODE (r_name) == IDENTIFIER_NODE);
+	    tree seen = lookup_name (r_name);
 	    if (seen
 		&& TREE_CODE (seen) == PARM_DECL
 		&& DECL_CONTEXT (seen)
 		&& DECL_CONTEXT (seen) == fndecl)
 	      {
 		auto_diagnostic_group d;
-		error_at (EXPR_LOCATION (CONTRACT_STATEMENT (ca)),
+		location_t id_l = location_wrapper_p (id)
+				  ? EXPR_LOCATION (id)
+				  : DECL_SOURCE_LOCATION (id);
+		location_t co_l = EXPR_LOCATION (CONTRACT_STATEMENT (ca));
+		if (id_l != UNKNOWN_LOCATION)
+		  co_l = make_location (id_l, get_start (co_l), get_finish (co_l));
+		error_at (co_l,
 			  "contract postcondition result names must not shadow"
 			  " function parameters");
 		inform (DECL_SOURCE_LOCATION (seen),

gcc/cp/parser.cc

@@ -31502,6 +31502,8 @@ cp_parser_contract_attribute_spec (cp_parser *parser, tree attribute,
       DEFPARSE_INSTANTIATIONS (condition) = NULL;
 
       /* And its corresponding contract.  */
+      if (identifier)
+	identifier.maybe_add_location_wrapper ();
       contract = grok_contract (attribute, mode, identifier, condition, loc);
     }
   else
@@ -31588,16 +31590,19 @@ void cp_parser_late_contract_condition (cp_parser *parser,
   if (TREE_CODE (condition) != DEFERRED_PARSE)
     return;
 
-  tree identifier = NULL_TREE;
+  tree r_ident = NULL_TREE;
   if (TREE_CODE (contract) == POSTCONDITION_STMT)
-    identifier = POSTCONDITION_IDENTIFIER (contract);
+    r_ident = POSTCONDITION_IDENTIFIER (contract);
 
   tree type = TREE_TYPE (TREE_TYPE (fn));
-  if (identifier)
+  location_t r_loc = UNKNOWN_LOCATION;
+  if (r_ident)
     {
-      /* TODO: Can we guarantee that the identifier has a location? */
-      location_t loc = cp_expr_location (contract);
-      if (!check_postcondition_result (fn, type, loc))
+      r_loc = EXPR_LOCATION (r_ident);
+      r_ident = tree_strip_any_location_wrapper (r_ident);
+      if (r_loc == UNKNOWN_LOCATION)
+	r_loc = cp_expr_location (contract);
+      if (!check_postcondition_result (fn, type, r_loc))
 	{
 	  invalidate_contract (contract);
 	  return;
@@ -31649,16 +31654,17 @@ void cp_parser_late_contract_condition (cp_parser *parser,
   should_constify_contract = should_constify;
   /* Build a fake variable for the result identifier.  */
   tree result = NULL_TREE;
-  if (identifier)
+  if (r_ident)
     {
-      result = make_postcondition_variable (identifier, type);
+      cp_expr result_id (r_ident, r_loc);
+      result = make_postcondition_variable (result_id, type);
       ++processing_template_decl;
     }
   cp_expr parsed_condition = cp_parser_conditional_expression (parser);
   /* Commit to changes.  */
   update_late_contract (contract, result, parsed_condition);
   /* Leave our temporary scope for the postcondition result.  */
-  if (identifier)
+  if (r_ident)
     --processing_template_decl;
   processing_postcondition = old_pc;
   should_constify_contract = old_const;