[PATCH v2 5/5] docs: automarkup.py: Allow automatic cross-reference inside C namespace

["Nícolas F. R. A. Prado" <nfraprado@protonmail.com>]

Sphinx 3.1 introduced namespaces for C cross-references. With this,
each C domain type/function declaration is put inside the namespace that
was active at the time of its declaration.

To support automatic cross-reference inside C namespaces:
- Save the C namespace used in each doc file (if any) at the source-read
  phase, in the beginning of the Sphinx process.
- When making the automarkup, if any namespace was used in the current
  file, try to cross-reference to the symbol inside of it before trying
  in the global namespace.

To make the first step possible, disable the parallel_read_safe option
in Sphinx, since the dictionary that maps the files to the C namespaces
can't be concurrently updated. This unfortunately increases the build
time of the documentation.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@protonmail.com>
---
 Documentation/sphinx/automarkup.py | 130 ++++++++++++++++++-----------
 1 file changed, 82 insertions(+), 48 deletions(-)

diff --git a/Documentation/sphinx/automarkup.py b/Documentation/sphinx/automarkup.py
index 409dbc4100de..bca8cf5f519d 100644
--- a/Documentation/sphinx/automarkup.py
+++ b/Documentation/sphinx/automarkup.py
@@ -45,6 +45,8 @@ RE_typedef = re.compile(r'\b(typedef)\s+([a-zA-Z_]\w+)', flags=re.ASCII)
 #
 RE_doc = re.compile(r'\bDocumentation(/[\w\-_/]+)(\.\w+)*')
 
+RE_namespace = re.compile(r'^\s*..\s*c:namespace::\s*(\S+)\s*$')
+
 #
 # Reserved C words that we should skip when cross-referencing
 #
@@ -62,6 +64,8 @@ Skipfuncs = [ 'open', 'close', 'read', 'write', 'fcntl', 'mmap',
               'select', 'poll', 'fork', 'execve', 'clone', 'ioctl',
               'socket' ]
 
+c_namespace = {}
+
 def markup_refs(docname, app, node):
     t = node.astext()
     done = 0
@@ -120,30 +124,42 @@ def markup_func_ref_sphinx3(docname, app, match):
     #
     # Go through the dance of getting an xref out of the C domain
     #
-    target = match.group(2)
+    base_target = match.group(2)
     target_text = nodes.Text(match.group(0))
     xref = None
-    if not (target in Skipfuncs or target in Skipnames):
-        for class_s, reftype_s in zip(class_str, reftype_str):
-            lit_text = nodes.literal(classes=['xref', 'c', class_s])
-            lit_text += target_text
-            pxref = addnodes.pending_xref('', refdomain = 'c',
-                                          reftype = reftype_s,
-                                          reftarget = target, modname = None,
-                                          classname = None)
-            #
-            # XXX The Latex builder will throw NoUri exceptions here,
-            # work around that by ignoring them.
-            #
-            try:
-                xref = cdom.resolve_xref(app.env, docname, app.builder,
-                                         reftype_s, target, pxref,
-                                         lit_text)
-            except NoUri:
-                xref = None
-
-            if xref:
-                return xref
+    possible_targets = [base_target]
+    # Check if this document has a namespace, and if so, try
+    # cross-referencing inside it first.
+    try:
+        namespace = c_namespace[docname]
+    except KeyError:
+        pass
+    else:
+        possible_targets.insert(0, namespace + "." + base_target)
+
+    if base_target not in Skipnames:
+        for target in possible_targets:
+            if target not in Skipfuncs:
+                for class_s, reftype_s in zip(class_str, reftype_str):
+                    lit_text = nodes.literal(classes=['xref', 'c', class_s])
+                    lit_text += target_text
+                    pxref = addnodes.pending_xref('', refdomain = 'c',
+                                                  reftype = reftype_s,
+                                                  reftarget = target, modname = None,
+                                                  classname = None)
+                    #
+                    # XXX The Latex builder will throw NoUri exceptions here,
+                    # work around that by ignoring them.
+                    #
+                    try:
+                        xref = cdom.resolve_xref(app.env, docname, app.builder,
+                                                 reftype_s, target, pxref,
+                                                 lit_text)
+                    except NoUri:
+                        xref = None
+
+                    if xref:
+                        return xref
 
     return target_text
 
@@ -171,34 +187,43 @@ def markup_c_ref(docname, app, match):
     #
     # Go through the dance of getting an xref out of the C domain
     #
-    target = match.group(2)
+    base_target = match.group(2)
     target_text = nodes.Text(match.group(0))
     xref = None
-    if not ((match.re == RE_function and target in Skipfuncs)
-            or (target in Skipnames)):
-        lit_text = nodes.literal(classes=['xref', 'c', class_str[match.re]])
-        lit_text += target_text
-        pxref = addnodes.pending_xref('', refdomain = 'c',
-                                      reftype = reftype_str[match.re],
-                                      reftarget = target, modname = None,
-                                      classname = None)
-        #
-        # XXX The Latex builder will throw NoUri exceptions here,
-        # work around that by ignoring them.
-        #
-        try:
-            xref = cdom.resolve_xref(app.env, docname, app.builder,
-                                     reftype_str[match.re], target, pxref,
-                                     lit_text)
-        except NoUri:
-            xref = None
-    #
-    # Return the xref if we got it; otherwise just return the plain text.
-    #
-    if xref:
-        return xref
+    possible_targets = [base_target]
+    # Check if this document has a namespace, and if so, try
+    # cross-referencing inside it first.
+    try:
+        namespace = c_namespace[docname]
+    except KeyError:
+        pass
     else:
-        return target_text
+        possible_targets.insert(0, namespace + "." + base_target)
+
+    if base_target not in Skipnames:
+        for target in possible_targets:
+            if not (match.re == RE_function and target in Skipfuncs):
+                lit_text = nodes.literal(classes=['xref', 'c', class_str[match.re]])
+                lit_text += target_text
+                pxref = addnodes.pending_xref('', refdomain = 'c',
+                                              reftype = reftype_str[match.re],
+                                              reftarget = target, modname = None,
+                                              classname = None)
+                #
+                # XXX The Latex builder will throw NoUri exceptions here,
+                # work around that by ignoring them.
+                #
+                try:
+                    xref = cdom.resolve_xref(app.env, docname, app.builder,
+                                             reftype_str[match.re], target, pxref,
+                                             lit_text)
+                except NoUri:
+                    xref = None
+
+                if xref:
+                    return xref
+
+    return target_text
 
 #
 # Try to replace a documentation reference of the form Documentation/... with a
@@ -246,9 +271,18 @@ def auto_markup(app, doctree, name):
             if not isinstance(node.parent, nodes.literal):
                 node.parent.replace(node, markup_refs(name, app, node))
 
+def save_c_namespace(app, docname, source):
+    lines = iter(source[0].splitlines(True))
+    for l in lines:
+        match = RE_namespace.search(l)
+        if match:
+            c_namespace[docname] = match.group(1)
+            return
+
 def setup(app):
+    app.connect('source-read', save_c_namespace)
     app.connect('doctree-resolved', auto_markup)
     return {
-        'parallel_read_safe': True,
+        'parallel_read_safe': False,
         'parallel_write_safe': True,
         }
-- 
2.28.0