[patch] New libstdc++ docs on testing and library versioning

[Jonathan Wakely]

On 05/08/16 01:37 +0100, Jonathan Wakely wrote:
>The core of the new guidelines for writing tests is this:
>
>[begin]
> Test cases that use features of a particular C++ standard should
> specify the minimum required standard as an effective target:
>
>   // { dg-do run { target c++11 } }
>
> or
>
>   // { dg-require-effective-target c++11 }
>
> Specifying the minimum required standard for a test allows it to be
> run using later standards, so that we can verify that C++11
> components still work correctly when compiled as C++14 or later.

I forgot to say that this is the main reason for all the testsuite
work I've been doing for the last couple of weeks. We have hundreds of
tests using { dg-options "-std=gnu++11" } which means that we're not
testing huge chunks of the library with the default -std=gnu++14
option.

By using { dg-do what { target c++11 } } the default testsuite options
will run the test with the default -std setting, but we can optionally
also run them with -std=gnu++11, and -std=gnu++17, and other
variations (which I'm going to be doing nightly).

So I want the docs to describe how I think we should be writing tests.