[libc++] Document that internal aliases should be marked _LIBCPP_NODEBUG

[philnik777]

In #118710 we've added _LIBCPP_NODEBUG to all internal aliases, but didn't actually document it. This patch adds documentation by adding the new requirement and reasoning to the coding guidelines.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

In #118710 we've added _LIBCPP_NODEBUG to all internal aliases, but didn't actually document it. This patch adds documentation by adding the new requirement and reasoning to the coding guidelines.

---

Full diff: https://github.com/llvm/llvm-project/pull/122175.diff

1 Files Affected:

• (modified) libcxx/docs/CodingGuidelines.rst (+10)

diff --git a/libcxx/docs/CodingGuidelines.rst b/libcxx/docs/CodingGuidelines.rst
index 1bb62072e886d1..0bad28b05b15ca 100644
--- a/libcxx/docs/CodingGuidelines.rst
+++ b/libcxx/docs/CodingGuidelines.rst
@@ -184,3 +184,13 @@ headers (which is sometimes required for ``constexpr`` support).
 
 When defining a function at the ABI boundary, it can also be useful to consider which attributes (like ``[[gnu::pure]]``
 and ``[[clang::noescape]]``) can be added to the function to improve the compiler's ability to optimize.
+
+library-internal type aliases should be annotated with ``_LIBCPP_NODEBUG``
+==========================================================================
+
+Libc++ has lots of internal type aliases. Accumulated, these can result in significant amounts of debug information that
+users don't care about usually, since users don't try to debug standard library facilities in most cases. For that
+reason, all library-internal type aliases should be annotated with ``_LIBCPP_NODEBUG`` to suppress compilers from
+generating said debug information.
+
+This is enforced by the clang-tidy check ``libcpp-nodebug-on-aliases``.

[ldionne]

Requesting changes for the review queue status.