docs/sphinx/kerneldoc.py: Honour --enable-werror

Currently, the kerneldoc Sphinx plugin doesn't honour the
--enable-werror configure option, so its warnings are never fatal.
This is because although we do pass sphinx-build the -W switch, the
warnings from kerneldoc are produced by the scripts/kernel-doc script
directly and don't go through Sphinx's "emit a warning" function.

When --enable-werror is in effect, pass sphinx-build an extra
argument -Dkerneldoc_werror=1.  The kerneldoc plugin can then use
this to determine whether it should be passing the kernel-doc script
-Werror.

We do this because there is no documented mechanism for
a Sphinx plugin to determine whether sphinx-build was
passed -W or not; if one is provided then we can switch to
that at a later date:
https://github.com/sphinx-doc/sphinx/issues/11239

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230314114431.1096972-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

docs/sphinx/kerneldoc.py

@@ -74,6 +74,10 @@ class KernelDocDirective(Directive):
         # Sphinx versions
         cmd += ['-sphinx-version', sphinx.__version__]
 
+        # Pass through the warnings-as-errors flag
+        if env.config.kerneldoc_werror:
+            cmd += ['-Werror']
+
         filename = env.config.kerneldoc_srctree + '/' + self.arguments[0]
         export_file_patterns = []
 
@@ -167,6 +171,7 @@ def setup(app):
     app.add_config_value('kerneldoc_bin', None, 'env')
     app.add_config_value('kerneldoc_srctree', None, 'env')
     app.add_config_value('kerneldoc_verbosity', 1, 'env')
+    app.add_config_value('kerneldoc_werror', 0, 'env')
 
     app.add_directive('kernel-doc', KernelDocDirective)