[C++ Patch] PR 48630 (PR 31423)

Gabriel Dos Reis gdr@integrable-solutions.net
Thu Oct 20 05:48:00 GMT 2011

On Wed, Oct 19, 2011 at 7:47 PM, Gabriel Dos Reis
<gdr@integrable-solutions.net> wrote:
> On Wed, Oct 19, 2011 at 7:09 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>> On 10/20/2011 02:00 AM, Gabriel Dos Reis wrote:
>>> I believe the effect of your new patch is that if will
>>> always emit the suggest "did you forget "()"?" for member functions,
>>> even in the case where the current suggestion is correct.
>>> Using the type context would prevent that regression.
>> If you could give some guidance about the way to implement this, I may try
>> over the next few days, otherwise probably I will have to give up for now (I
>> assigned myself other PRs already), but it would be a pity, this PR has been
>> reported 2 times by different people, apparently it's quite misleading.
>> Anyway, I'm not assigned to the bug, even if I will not be able to actually
>> help, it would be nice if you could attach to the audit trail a couple of
>> nasty examples beyond what already considered in the analyses therein (both
>> PRs)
>> Thanks!
>> Paolo.
> I think I made a suggestion in my previous message:
>  -- decouple this particular diagnostic from 'incomplete type' error.
>      Because it has nothing to do with incomplete type error.
>  -- once the diagnostic is decoupled, you could "grep" for all the
>    places where cxx_incomplete_type_error or cxx_incomplete_type_diagnostic
>    is called from.
> My comments weren't in terms of "owenership" of the PR.
> I would not necessarily say that they are nasty cases.
> I know you don't like history but I believe it is important to
> understand how the diagnostics came to be before fixing
> them to prevent regressions -- or to purposefully break with
> the past.
> The reason why we have this suggestion in the first place is
> because g++ supports the MS extension known as "bound member
> function", e.g. something like &c.f, where c is an object and f is a
> non-static member function.  It isn't ISO C++, but it is GNU C++
> wth -fms-extensions.  A simple testcase is
> struct C {
>   int f() { return 1; }
>   int g() { return 2; }
> };
> int f(C&c) {
>   return &c.g == &c.f;
> }
> If you compile that program fragment with -fms-extensions, g++ will
> accept it.  If you remove one of the '&', you get the diagnostic that
> you want to fix.  You realize that if you use '()', you get another
> type incompatible error, but not if you use '&' as suggested.
> So the diagnostic could use both type context and test for -fms-extensions.
> PS: more than a decade ago, I suggested removing this but people disagreed.

Another acceptable fix is to
  -- leave the current diagnostic as is if -fms-extensions
  -- suggest '()' is member function
  -- otherwise suggest '&'.

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