c++, contracts: Handle contract-specific location wrappers.

Contract conditions use location wrappers on more tree types than
the generic code.  This means that we need to take care of them
when tsubst-ing, otherwise the geneic code is getting given un-
expected input (and, predicatably, it does not work).

This is a more general problem upstream - but "just applying
wrappers" to more trees in the generic code is going to need
a lot of work (it fails quite spectacularly) unrelated to
contracts.

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

Author: iains

gcc/cp/contracts.cc

@@ -2691,18 +2691,26 @@ remap_and_emit_conditions (tree fn, tree condfn, tree_code code)
 tree
 finish_contract_condition (cp_expr condition)
 {
+  if (!condition || error_operand_p (condition))
+    return condition;
+
   /* Ensure we have the condition location saved in case we later need to
      emit a conversion error during template instantiation and wouldn't
-     otherwise have it.  */
-  if (!CAN_HAVE_LOCATION_P (condition) || EXCEPTIONAL_CLASS_P (condition))
-    {
-      condition = build1_loc (condition.get_location (), VIEW_CONVERT_EXPR,
+     otherwise have it.  This differs from maybe_wrap_with_location in that
+     it allows wrappers on EXCEPTIONAL_CLASS_P which includes CONSTRUCTORs.  */
+  if (!CAN_HAVE_LOCATION_P (condition)
+      && condition.get_location () != UNKNOWN_LOCATION)
+    {
+      tree_code code
+	= (((CONSTANT_CLASS_P (condition) && TREE_CODE (condition) != STRING_CST)
+	    || (TREE_CODE (condition) == CONST_DECL && !TREE_STATIC (condition)))
+	  ? NON_LVALUE_EXPR : VIEW_CONVERT_EXPR);
+      condition = build1_loc (condition.get_location (), code,
 			      TREE_TYPE (condition), condition);
       EXPR_LOCATION_WRAPPER_P (condition) = true;
     }
 
-  if (condition == error_mark_node
-      || type_dependent_expression_p (condition))
+  if (type_dependent_expression_p (condition))
     return condition;
 
   return condition_conversion (condition);

gcc/cp/pt.cc

@@ -12057,11 +12057,19 @@ tsubst_contract (tree decl, tree t, tree args, tsubst_flags_t complain,
     /* Make the variable available for lookup.  */
     register_local_specialization (newvar, oldvar);
 
-  CONTRACT_CONDITION (r)
-      = tsubst_expr (CONTRACT_CONDITION (t), args, complain, in_decl);
-
-  /* The condition is converted to bool.  */
-  CONTRACT_CONDITION (r) = finish_contract_condition (CONTRACT_CONDITION (r));
+  /* Contract conditions have a wider application of location wrappers than
+     other trees which will not work with the generic handling in tsubst_expr,
+     remove the wrapper here...  */
+  location_t cond_l = EXPR_LOCATION (CONTRACT_CONDITION (t));
+  tree cond_t = tree_strip_any_location_wrapper (CONTRACT_CONDITION (t));
+
+  /* ... and substitute with the contained expression.  */
+  cond_t = tsubst_expr (cond_t, args, complain, in_decl);
+
+  /* Converted to bool, if possible, and then re-apply a location wrapper
+     when required.  */
+  cp_expr new_condition (cond_t, cond_l);
+  CONTRACT_CONDITION (r) = finish_contract_condition (new_condition);
 
   /* And the comment.  */
   /* TODO : this does not do anything at the moment. The CONTRACT_COMMENT is