[C++ Patch] Fix some locations

[Paolo Carlini]

Hi,

On 01/06/2018, 23:29, Jason Merrill wrote:
> On Fri, Jun 1, 2018 at 5:03 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>> while working on some bugs I noticed that in a few places in decl.c we could
>> do better in terms of locations within the current infrastructure, some
>> simple, straightforward improvements. I'm attaching below a tiny first
>> patch, more to follow, I hope.
>>
>> For example, a function which could be improved in many places is
>> grok_ctor_properties and, before going ahead, I'd like to ask about
>> something I noticed yesterday:
>>
>>    /* There can be no default arguments.  */
>>    for (tree arg = argtypes; arg != void_list_node; arg = TREE_CHAIN (arg))
>>      if (TREE_PURPOSE (arg))
>>        {
>>          TREE_PURPOSE (arg) = NULL_TREE;
>>          if (operator_code == POSTINCREMENT_EXPR
>>              || operator_code == POSTDECREMENT_EXPR)
>>            pedwarn (input_location, OPT_Wpedantic,
>>                     "%qD cannot have default arguments", decl);
>>          else
>>            {
>>              error ("%qD cannot have default arguments", decl);
>>              return false;
>>            }
>>        }
>>
>> the special casing seems weird, so far I haven't been able to find anything
>> in the standard about it and all the other compilers I have at hand (Oracle,
>> Intel, Clang) don't seem to have it. Shall we keep it or not? Maybe with an
>> additional comment explaining the rationale? The affected testcases would be
>> parse/defarg11.C and g++.jason/operator.C.
> I think in the olden days, with a default argument one function could
> support both prefix and postfix inc/decrement syntax:
>
> struct A {
>    A& operator++(int = 0);
> };
>
> int main()
> {
>    A a;
>    ++a;
>    a++;
> }
>
> ...but that hasn't actually worked in forever, so it shouldn't be a
> problem to make the ++ case an error, too.
Thanks for the explanation. If we can remove the special casing, fixing 
some other issues will be easier, for example setting TREE_PURPOSE 
unconditionally error_mark_node fixes a Bugzilla bug (I don't have the 
number with me, more when I'm back home next week ;)

Thanks,
Paolo.