Re: [PATCH 1/2] PR c++/91436 fix C++ dialect for std::make_unique fix-it hint

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2019-08-14 at 16:53 +0100, Jonathan Wakely wrote:
> On 14/08/19 10:39 -0400, David Malcolm wrote:
> > On Wed, 2019-08-14 at 12:02 +0100, Jonathan Wakely wrote:
> > > On 13/08/19 16:07 -0400, Jason Merrill wrote:
> > > > On 8/13/19 9:32 AM, Jonathan Wakely wrote:
> > > > >     * g++.dg/lookup/missing-std-include-6.C: Don't check
> > > > > make_unique in
> > > > >     test that runs for C++11.
> > > > 
> > > > I'm not comfortable removing this test coverage
> > > > entirely.  Doesn't
> > > > it
> > > > give a useful diagnostic in C++11 mode as well?
> > > 
> > > It does:
> > > 
> > > mu.cc:3:15: error: 'make_unique' is not a member of 'std'
> > >     3 | auto p = std::make_unique<int>();
> > >       |               ^~~~~~~~~~~
> > > mu.cc:3:15: note: 'std::make_unique' is only available from C++14
> > > onwards
> > > mu.cc:3:27: error: expected primary-expression before 'int'
> > >     3 | auto p = std::make_unique<int>();
> > >       |                           ^~~
> > > 
> > > So we can add it to g++.dg/lookup/missing-std-include-8.C
> > > instead,
> > > which runs for c++98_only and checks for the "is only available
> > > for"
> > > cases. Here's a patch doing that.
> > 
> > FWIW this eliminates the testing that when we do have C++14
> > onwards,
> > that including <memory> is suggested.
> 
> Do we really care?
> 
> Are we testing that *every* entry in the array gives the right answer
> for both missing-header and bad-std-option, or are we just testing a
> subset of them to be sure the logic works as expected?
> 
> Because if we're testing every entry then:
> 
> 1) we're missing LOTS of tests, and
> 
> 2) we're just as likely to test the wrong thing and not actually
> catch
>    bugs (as was already happening for both make_unique and
>    complex_literals).
> 
> > Maybe we need a C++14-onwards missing-std-include-* test, and to
> > move
> > the existing test there?  (and to add the new test for before-C++-
> > 14)
> 
> We could, but is it worth it?

Fair enough.

Dave