Add compiler warning tracking tooling failure remediation guidance (#1364)

Co-authored-by: Ezio Melotti <[email protected]>
Co-authored-by: Hugo van Kemenade <[email protected]>

Author: 3 people

development-tools/index.rst

@@ -9,3 +9,4 @@ Development tools
    gdb
    clang
    coverity
+   warnings

development-tools/warnings.rst

@@ -0,0 +1,51 @@
+.. warnings:
+
+Tools for tracking compiler warnings
+====================================
+
+.. highlight:: bash
+
+The compiler warning tracking tooling is intended to alert developers about new
+compiler warnings introduced by their contributions. The tooling consists of
+a Python script which is ran by the following GitHub workflows:
+
+* Ubuntu/build and test (:cpy-file:`.github/workflows/reusable-ubuntu.yml`)
+* macOS/build and test (:cpy-file:`.github/workflows/reusable-macos.yml`)
+
+You can check the documentation for the :cpy-file:`Tools/build/check_warnings.py` tool
+by running::
+
+   python Tools/build/check_warnings.py --help
+
+The script can be run locally by providing the compiler output file
+(where the output is saved) and the compiler output type
+(either ``json`` or ``clang``) to see a list of unique warnings::
+
+   python Tools/build/check_warnings.py --compiler-output-file-path=compiler_output.txt --compiler-output-type=json
+
+.. note:: The ``-fdiagnostics-format=json`` flag is required when compiling with GCC
+          for the script to properly parse the compiler output.
+
+.. _warning-check-failure:
+
+What to do if a warning check fails GitHub CI
+---------------------------------------------
+
+The :cpy-file:`Tools/build/check_warnings.py` tool will fail if the compiler generates
+more or less warnings than expected for a given source file as defined in the
+platform-specific warning ignore file. The warning ignore file is either
+:cpy-file:`Tools/build/.warningignore_ubuntu` or
+:cpy-file:`Tools/build/.warningignore_macos` depending on the platform.
+
+If a warning check fails with:
+
+* Unexpected warnings
+    * Attempt to refactor the code to avoid the warning.
+    * If it is not possible to avoid the warning document in the PR why it is
+      reasonable to ignore and add the warning to the platform-specific
+      warning ignore file. If the file exists in the warning ignore file
+      increment the count by the number of newly introduced warnings.
+* Unexpected improvements (less warnings)
+    * Document in the PR that the change reduces the number of compiler
+      warnings. Decrement the count in the platform-specific warning
+      ignore file or remove the file if the count is now zero.