docs: cdomain.py: add support for a new Sphinx 3.1+ tag

Since Sphinx 3.0, the C domain code was rewritten, but only
after version 3.1 it got support for setting namespaces on
C domains, with is something that it is required, in order to
document system calls, like ioctl() and others.

As part of changing the documentation subsystem to properly
build with Sphinx 3.1+, add support for such new tag:

	.. c:namespace::"

Such tag optionally replaces the optional "name" tag for functions,
setting a single namespace domain for all C references found
at the file.

With that, it should be possible to convert existing
documentation to be compatible with both Sphinx 1.x/2.x and
3.1+.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/sphinx/cdomain.py

@@ -40,14 +40,56 @@ from sphinx import addnodes
 from sphinx.domains.c import c_funcptr_sig_re, c_sig_re
 from sphinx.domains.c import CObject as Base_CObject
 from sphinx.domains.c import CDomain as Base_CDomain
+from itertools import chain
+import re
 
-__version__  = '1.0'
+__version__  = '1.1'
 
 # Get Sphinx version
 major, minor, patch = sphinx.version_info[:3]
 
+# Namespace to be prepended to the full name
+namespace = None
+
+#
+# Handle trivial newer c domain tags that are part of Sphinx 3.1 c domain tags
+# - Store the namespace if ".. c:namespace::" tag is found
+
+RE_namespace = re.compile(r'^\s*..\s*c:namespace::\s*(\S+)\s*$')
+
+def markup_namespace(match):
+    global namespace
+
+    namespace = match.group(1)
+
+    return ""
+
+def c_markups(app, docname, source):
+    result = ""
+    markup_func = {
+        RE_namespace: markup_namespace,
+    }
+
+    lines = iter(source[0].splitlines(True))
+    for n in lines:
+        match_iterators = [regex.finditer(n) for regex in markup_func]
+        matches = sorted(chain(*match_iterators), key=lambda m: m.start())
+        for m in matches:
+            n = n[:m.start()] + markup_func[m.re](m) + n[m.end():]
+
+        result = result + n
+
+    source[0] = result
+
+#
+# Now implements support for the cdomain namespacing logic
+#
+
 def setup(app):
 
+    # Handle easy Sphinx 3.1+ simple new tags: :c:expr and .. c:namespace::
+    app.connect('source-read', c_markups)
+
     if (major == 1 and minor < 8):
         app.override_domain(CDomain)
     else:
@@ -75,6 +117,8 @@ class CObject(Base_CObject):
         function-like macro, the name of the macro is returned. Otherwise
         ``False`` is returned.  """
 
+        global namespace
+
         if not self.objtype == 'function':
             return False
 
@@ -107,11 +151,16 @@ class CObject(Base_CObject):
             param += nodes.emphasis(argname, argname)
             paramlist += param
 
+        if namespace:
+            fullname = namespace + "." + fullname
+
         return fullname
 
     def handle_signature(self, sig, signode):
         """Transform a C signature into RST nodes."""
 
+        global namespace
+
         fullname = self.handle_func_like_macro(sig, signode)
         if not fullname:
             fullname = super(CObject, self).handle_signature(sig, signode)
@@ -122,6 +171,10 @@ class CObject(Base_CObject):
             else:
                 # FIXME: handle :name: value of other declaration types?
                 pass
+        else:
+            if namespace:
+                fullname = namespace + "." + fullname
+
         return fullname
 
     def add_target_and_index(self, name, sig, signode):