docs/ci: treat warnings as errors

When we moved building the docs to Meson, we accidentally dropped the -W
flag that we used to have. This lead to us no longer detecting certain
problems in the docs, which is unfortunate.

Let's bring this back gated by the werror meson-option, and wire that up
on the CI end.

Fixes: fdd204538b ("ci: build docs using meson")
Reviewed-by: Dylan Baker <None>
(cherry picked from commit cf07e89d06)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32852>

.pick_status.json

@@ -24,7 +24,7 @@
         "description": "docs/ci: treat warnings as errors",
         "nominated": true,
         "nomination_type": 2,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "fdd204538b93e17cecd32786603e0e2452e459c4",
         "notes": null

docs/gitlab-ci.yml

@@ -10,6 +10,7 @@
     - meson setup _build -D prefix=$(pwd) --auto-features=disabled
       -D vulkan-drivers="" -D gallium-drivers="" -D platforms=[] -D glx=disabled
       -D video-codecs="" -D html-docs=enabled -D html-docs-path=public
+      -D werror=true
     - meson compile -C _build
     - meson install -C _build
 

docs/meson.build

@@ -11,12 +11,18 @@ assert Version(hawkmoth.__version__) >= Version("0.16.0")
   error_message: 'hawkmoth >= 0.16.0 required'
 )
 
+sphinx_args = []
+if get_option('werror')
+  sphinx_args += '-W'
+endif
+
 html_docs = custom_target(
   'html',
   depfile: 'docs.d',
   depend_files: files('conf.py'),
   command: [sphinx, '-b', 'html', '-q',
             '-Ddepfile=@DEPFILE@',
+            sphinx_args,
             meson.current_source_dir(), '@OUTPUT@'],
   output: 'html',
   build_by_default: get_option('html-docs').enabled(),