================
@@ -0,0 +1,92 @@
+============================
+Warning suppression mappings
+============================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+Warning suppression mappings enables users to suppress clang's diagnostics in a
+per-file granular manner. Enabling enforcement of diagnostics in specific parts
+of the project, even if there are violations in dependencies or other parts of
+the codebase.
+
+Goal and usage
+==============
+
+Clang allows diagnostics to be configured at a translation-unit granularity.
+If a foo.cpp is compiled with -Wfoo, all transitively included headers also
need
+to be clean. Hence turning on new warnings at large codebases is quite
difficult
+today:
+- It requires cleaning up all the existing warnings, which might not be
possible
+ when some dependencies aren't in project owner's control.
+- Preventing backsliding in the meanwhile as the diagnostic can't be enforced
at
+ all until codebase is cleaned up.
+
+Warning suppression mappings aims to alleviate some of these concerns by making
+diagnostic configuration granularity finer, at a source file level.
+
+To achieve this, user may create a file listing which diagnostic groups to
+suppress in which files, and pass it as a command line argument to clang with
+``--warning-suppression-mappings`` flag.
+
+Note that this mechanism won't enable any diagnostics on its own. Users should
+still turn on warnings in their compilations with explicit ``-Wfoo`` flags.
+
+Example
+=======
+
+.. code-block:: bash
+
+ $ cat my/user/code.cpp
+ #include <foo/bar.h>
+ namespace { void unused_func1(); }
+
+ $ cat foo/bar.h
+ namespace { void unused_func2(); }
+
+ $ cat suppression_mappings.txt
+ # Suppress -Wunused warnings in all files, apart from the ones under `foo/`.
+ [unused]
+ src:*
+ src:*foo/*=emit
+ $ clang -Wunused --warning-suppression-mappings=suppression_mappings.txt
my/user/code.cpp
+ # prints warning: unused function 'unused_func2', but no warnings for
`unused_func1`.
+
+Format
+======
+
+Warning suppression mappings uses a format similar to
----------------
AaronBallman wrote:
"similar to" really worries me; if it's not "the same as" then it's adding a
truly custom format.
https://github.com/llvm/llvm-project/pull/112517
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