gh-126609: Revert Availability Directive changes

Doc/conf.py

@@ -23,7 +23,6 @@
 # Our custom Sphinx extensions are found in Doc/Tools/extensions/
 extensions = [
     'audit_events',
-    'availability',
     'c_annotations',
     'changes',
     'glossary_search',

Doc/tools/extensions/pyspecific.py

@@ -18,6 +18,7 @@
 from docutils.utils import unescape
 from sphinx import addnodes
 from sphinx.domains.python import PyFunction, PyMethod, PyModule
+from sphinx.util import logging
 from sphinx.locale import _ as sphinx_gettext
 from sphinx.util.docutils import SphinxDirective
 
@@ -90,6 +91,76 @@ def run(self):
         return [pnode]
 
 
+# Support for documenting platform availability
+
+class Availability(SphinxDirective):
+
+    has_content = True
+    required_arguments = 1
+    optional_arguments = 0
+    final_argument_whitespace = True
+
+    # known platform, libc, and threading implementations
+    known_platforms = frozenset({
+        "AIX", "Android", "BSD", "DragonFlyBSD", "Emscripten", "FreeBSD",
+        "GNU/kFreeBSD", "Linux", "NetBSD", "OpenBSD", "POSIX", "Solaris",
+        "Unix", "VxWorks", "WASI", "Windows", "macOS", "iOS",
+        # libc
+        "BSD libc", "glibc", "musl",
+        # POSIX platforms with pthreads
+        "pthreads",
+    })
+
+    def run(self):
+        availability_ref = ':ref:`Availability <availability>`: '
+        avail_nodes, avail_msgs = self.state.inline_text(
+            availability_ref + self.arguments[0],
+            self.lineno)
+        pnode = nodes.paragraph(availability_ref + self.arguments[0],
+                                '', *avail_nodes, *avail_msgs)
+        self.set_source_info(pnode)
+        cnode = nodes.container("", pnode, classes=["availability"])
+        self.set_source_info(cnode)
+        if self.content:
+            self.state.nested_parse(self.content, self.content_offset, cnode)
+        self.parse_platforms()
+
+        return [cnode]
+
+    def parse_platforms(self):
+        """Parse platform information from arguments
+        Arguments is a comma-separated string of platforms. A platform may
+        be prefixed with "not " to indicate that a feature is not available.
+        Example::
+           .. availability:: Windows, Linux >= 4.2, not WASI
+        Arguments like "Linux >= 3.17 with glibc >= 2.27" are currently not
+        parsed into separate tokens.
+        """
+        platforms = {}
+        for arg in self.arguments[0].rstrip(".").split(","):
+            arg = arg.strip()
+            platform, _, version = arg.partition(" >= ")
+            if platform.startswith("not "):
+                version = False
+                platform = platform[4:]
+            elif not version:
+                version = True
+            platforms[platform] = version
+
+        unknown = set(platforms).difference(self.known_platforms)
+        if unknown:
+            cls = type(self)
+            logger = logging.getLogger(cls.__qualname__)
+            logger.warning(
+                f"Unknown platform(s) or syntax '{' '.join(sorted(unknown))}' "
+                f"in '.. availability:: {self.arguments[0]}', see "
+                f"{__file__}:{cls.__qualname__}.known_platforms for a set "
+                "known platforms."
+            )
+
+        return platforms
+
+
 class PyCoroutineMixin(object):
     def handle_signature(self, sig, signode):
         ret = super(PyCoroutineMixin, self).handle_signature(sig, signode)
@@ -260,6 +331,7 @@ def setup(app):
     app.add_role('issue', issue_role)
     app.add_role('gh', gh_issue_role)
     app.add_directive('impl-detail', ImplementationDetail)
+    app.add_directive('availability', Availability)
     app.add_object_type('opcode', 'opcode', '%s (opcode)', parse_opcode_signature)
     app.add_object_type('pdbcommand', 'pdbcmd', '%s (pdb command)', parse_pdb_command)
     app.add_object_type('monitoring-event', 'monitoring-event', '%s (monitoring event)', parse_monitoring_event)