docs: conf.py: properly handle include and exclude patterns

When one does:
	make SPHINXDIRS="foo" htmldocs

All patterns would be relative to Documentation/foo, which
causes the include/exclude patterns like:

	include_patterns = [
		...
		f'foo/*.{ext}',
	]

to break. This is not what it is expected. Address it by
adding a logic to dynamically adjust the pattern when
SPHINXDIRS is used.

That allows adding parsers for other file types.

It should be noticed that include_patterns was added on
Sphinx 5.1:
	https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-include_patterns

So, a backward-compatible code is needed when we start
using it for real.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/429c9c670fe27860f5e4f29aaf72576a4ed52ad1.1750571906.git.mchehab+huawei@kernel.org

Documentation/conf.py

@@ -17,6 +17,66 @@ import os
 import sphinx
 import shutil
 
+# Get Sphinx version
+major, minor, patch = sphinx.version_info[:3]
+
+# Include_patterns were added on Sphinx 5.1
+if (major < 5) or (major == 5 and minor < 1):
+    has_include_patterns = False
+else:
+    has_include_patterns = True
+    # Include patterns that don't contain directory names, in glob format
+    include_patterns = ['**.rst']
+
+# Location of Documentation/ directory
+doctree = os.path.abspath('.')
+
+# Exclude of patterns that don't contain directory names, in glob format.
+exclude_patterns = []
+
+# List of patterns that contain directory names in glob format.
+dyn_include_patterns = []
+dyn_exclude_patterns = ['output']
+
+# Properly handle include/exclude patterns
+# ----------------------------------------
+
+def update_patterns(app, config):
+
+    """
+    On Sphinx, all directories are relative to what it is passed as
+    SOURCEDIR parameter for sphinx-build. Due to that, all patterns
+    that have directory names on it need to be dynamically set, after
+    converting them to a relative patch.
+
+    As Sphinx doesn't include any patterns outside SOURCEDIR, we should
+    exclude relative patterns that start with "../".
+    """
+
+    sourcedir = app.srcdir  # full path to the source directory
+    builddir = os.environ.get("BUILDDIR")
+
+    # setup include_patterns dynamically
+    if has_include_patterns:
+        for p in dyn_include_patterns:
+            full = os.path.join(doctree, p)
+
+            rel_path = os.path.relpath(full, start = app.srcdir)
+            if rel_path.startswith("../"):
+                continue
+
+            config.include_patterns.append(rel_path)
+
+    # setup exclude_patterns dynamically
+    for p in dyn_exclude_patterns:
+        full = os.path.join(doctree, p)
+
+        rel_path = os.path.relpath(full, start = app.srcdir)
+        if rel_path.startswith("../"):
+            continue
+
+        config.exclude_patterns.append(rel_path)
+
 # helper
 # ------
 
@@ -219,10 +279,6 @@ language = 'en'
 # Else, today_fmt is used as the format for a strftime call.
 #today_fmt = '%B %d, %Y'
 
-# List of patterns, relative to source directory, that match files and
-# directories to ignore when looking for source files.
-exclude_patterns = ['output']
-
 # The reST default role (used for this markup: `text`) to use for all
 # documents.
 #default_role = None
@@ -516,3 +572,6 @@ kerneldoc_srctree = '..'
 # the last statement in the conf.py file
 # ------------------------------------------------------------------------------
 loadConfig(globals())
+
+def setup(app):
+    app.connect('config-inited', update_patterns)