[libcxx-dev] How to check for a feature-test macro

[Stephan T. Lavavej via libcxx-dev]

(+Casey who also works on this)

When running libcxx's tests against MSVC's STL, we have an MSVC-internal skipped_tests.txt (full content available if requested) which says:

# *** MISSING STL FEATURES ***
# C++20 P0122R7 "<span>"
upstream\test\std\containers\views\types.pass.cpp
[...]

# C++20 P0355R7 "<chrono> Calendars And Time Zones"
upstream\test\std\utilities\time\days.pass.cpp
[...]

Updating this requires minimal effort. It's more problematic when existing tests are modified to test new features, since we have to skip the entire test even if only a small part is affected.

Guarding tests with feature-test macros in their source code (as opposed to "the LIT level", which I believe is machinery that we don't use) would be ideal, I think.

The annoying thing is when features are added without corresponding feature-test macros. There's a bunch of those right now. We'll probably need the skip-tests approach for those.

STL

-----Original Message-----
From: Jonathan Wakely <cxx at kayari.org> 
Sent: Monday, December 10, 2018 12:10 PM
To: ldionne at apple.com
Cc: Richard Smith <richard at metafoo.co.uk>; Marshall Clow <mclow.lists at gmail.com>; libcxx-dev at lists.llvm.org; Stephan T. Lavavej <stl at exchange.microsoft.com>; Billy O'Neal (VC LIBS) <bion at microsoft.com>
Subject: Re: [libcxx-dev] How to check for a feature-test macro

On Mon, 10 Dec 2018 at 19:47, Louis Dionne wrote:
> We should also see how other implementations that use our test suite feel about this (CCing them).

I only use your tests a few times a year, run by hand. If I get a load of FAILs because I've not implemented something yet and you have, that's not a problem. I don't expect to get 100% green when I run your tests.