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


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?


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