From 59a72da360e2eff53ef510261c3f6307148b52dc Mon Sep 17 00:00:00 2001
From: Michał Górny <mgorny@gentoo.org>
Date: Sat, 22 Feb 2020 18:15:51 +0100
Subject: Generate a Policy Index
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Signed-off-by: Michał Górny <mgorny@gentoo.org>
---
 exts/policyident.py | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 75 insertions(+), 3 deletions(-)

diff --git a/exts/policyident.py b/exts/policyident.py
index 6093c8c..7ecc9f2 100644
--- a/exts/policyident.py
+++ b/exts/policyident.py
@@ -2,13 +2,44 @@
 # (c) 2020 Michał Górny
 # 2-clause BSD license
 
+import collections
+
 from docutils import nodes
 
+from sphinx.domains import Index
 from sphinx.util import logging
 
 
 logger = logging.getLogger(__name__)
 
+Policy = collections.namedtuple('Policy', ('id', 'title', 'docname',
+                                           'chapter'))
+
+
+class PolicyIndex(Index):
+    name = 'policy-index'
+    localname = 'Policy Index'
+    shortname = 'Policy Index'
+
+    def generate(self, docnames=None):
+        env = self.domain.env
+        if not hasattr(env, 'policy_index'):
+            env.policy_index = []
+
+        entries = collections.defaultdict(list)
+        for p in env.policy_index:
+            if docnames is not None and p.docname not in docnames:
+                continue
+            entries[p.chapter].append(('PG' + p.id,  # name
+                                       0,            # subtype
+                                       p.docname,    # docname
+                                       'pg' + p.id,  # anchor
+                                       p.title,      # extra
+                                       '',           # qualifier
+                                       ''))          # descr
+
+        return ([(k, sorted(v)) for k, v in entries.items()], False)
+
 
 def find_pg_id(section):
     # first child should be title
@@ -17,7 +48,7 @@ def find_pg_id(section):
     # second child should be field list
     cl = section.children[1]
     if not isinstance(cl, nodes.field_list):
-        return None
+        return None, title.astext(), None
 
     for f in cl.traverse(nodes.field):
         fn = next(iter(f.traverse(nodes.field_name)))
@@ -29,20 +60,61 @@ def find_pg_id(section):
             if fv.astext() != iv:
                 raise RuntimeError('PG value must be 4 digits, zero-padded ({})'
                                    .format(iv))
-            return iv
+
+            el = section
+            titles = []
+            while el.parent is not None:
+                title = el.children[0]
+                assert isinstance(title, nodes.title)
+                titles.append(title.astext())
+                el = el.parent
+            # combine all section titles up to but excluding
+            # the chapter title
+            title = ': '.join(reversed(titles[:-1]))
+
+            return iv, title, titles[-1]
 
     logger.warning('%s: no PG identifier found', title.astext())
+    return None, title.astext(), None
 
 
 def on_doctree_read(app, doctree):
+    env = app.builder.env
+    if not hasattr(env, 'policy_index'):
+        env.policy_index = []
+
     for node in doctree.traverse(nodes.section):
-        pg_id = find_pg_id(node)
+        pg_id, title, chapter = find_pg_id(node)
         if pg_id is not None:
             node['ids'].insert(0, 'pg' + pg_id)
+            env.policy_index.append(Policy(pg_id, title, env.docname,
+                                           chapter))
+
+
+def on_env_purge_doc(app, env, docname):
+    if not hasattr(env, 'policy_index'):
+        return
+
+    env.policy_index = [p for p in env.policy_index
+                        if p.docname != docname]
+
+
+def on_env_merge_info(app, env, docnames, other):
+    if not hasattr(other, 'policy_index'):
+        return
+    if not hasattr(env, 'policy_index'):
+        env.policy_index = []
+
+    env.policy_index.extend(other.policy_index)
 
 
 def setup(app):
     app.connect('doctree-read', on_doctree_read)
+    app.connect('env-purge-doc', on_env_purge_doc)
+    app.connect('env-merge-info', on_env_merge_info)
+    app.add_index_to_domain('std', PolicyIndex)
     return {
         'version': '0',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
     }
-- 
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