[RFC][libc++] Use IWYU pragma's.

[mordante]

The tools IWYU/clangd can suggest to remove unused headers. This suggests to remove test_macros.h. Removing this header can break tests.

For example tests use
#ifndef TEST_HAS_NO_WIDE_CHARACTERS
test<wchar_t>();
#endif

Since developers typically have wide characters support, the header is not used. However, removing the header would break configurations that have wide characters disabled.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Mark de Wever (mordante)

Changes

The tools IWYU/clangd can suggest to remove unused headers. This suggests to remove test_macros.h. Removing this header can break tests.

For example tests use
#ifndef TEST_HAS_NO_WIDE_CHARACTERS
test<wchar_t>();
#endif

Since typically developers have wide characters the header is not used. The removal of the header breaks configurations that have wide characters disabled.

---

Full diff: https://github.com/llvm/llvm-project/pull/102191.diff

1 Files Affected:

• (modified) libcxx/test/support/test_macros.h (+6)

diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index 15fc5b69b52076..9dab5750a5f917 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -7,6 +7,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+// This header contains several configuration defines.
+// Removing the header would #ifndef TEST_FOO to unconditionally pass when
+// it's optionally defined in this header.
+//
+// IWYU pragma: always_keep
+
 #ifndef SUPPORT_TEST_MACROS_HPP
 #define SUPPORT_TEST_MACROS_HPP
 

[ldionne]

My preference would be to instead use 0-1 for TEST_HAS_XXX macros, since that also solves the existing problem that our test suite is not safe w.r.t. -Wundef. And it would solve the clang-tidy issues since we'd actually use the macro from the header.

[mordante]

As discussed at a libc++ monthly we want to move in the direction as suggested by @ldionne above.