Support multiple targets on one section properly

Apply transform before PropagateTargets to special-case the first target and
prioritize its ID and name. This makes references to the other targets point to
the last target rather than the section itself (which has the old ID).

Changelog: add::

sphinx_better_subsection.py

@@ -34,30 +34,30 @@ class PreferSectionTarget(Transform):
     .. code-block:: xml
 
         ...
-            <target refid="a">
-            <target refid="b">
-            <target refid="c">
-            <section ids="section-title a b c">
+            <target ids="['a']" names="['a']">
+            <target ids="['b']" names="['b']">
+            <target ids="['c']" names="['c']">
+            <section ids="section-title" names="Section\\ Title">
                 ...
 
     Transforming it gives:
 
     .. code-block:: xml
 
         ...
-            <target refid="a">
-            <target refid="b">
+            <target ids="['a']" names="['a']">
+            <target ids="['b']" names="['b']">
             <target refid="c">
-            <section ids="c section-title a b">
+            <section ids="c section-title" names="c Section\\ Title">
                 ...
 
     Note that the other IDs are all preserved; only the order is modified.
     Nested subsections are also checked.
 
     """
-    # Post processing priority from
-    # https://www.sphinx-doc.org/en/master/extdev/appapi.html?highlight=transform#sphinx.application.Sphinx.add_transform
-    default_priority = 700
+    # Run before `docutils.transforms.references.PropagateTransform` which has
+    # priority 260.
+    default_priority = 255
 
     def apply(self):
         """Docutils transform entry point"""
@@ -79,14 +79,55 @@ def apply(self):
             # Filter away nodes that aren't targets
             if not isinstance(last, nodes.target):
                 continue
-            # Internal hyperlink targets have refid (external ones have refuri)
-            if "refid" not in last:
+            # Filter away targets with content
+            if (
+                isinstance(last.parent, nodes.TextElement)
+                or last.hasattr("refid")
+                or last.hasattr("refuri")
+                or last.hasattr("refname")
+            ):
                 continue
-            refid = last["refid"]
-            assert refid in node["ids"]
+
+            # Store ID and name
+            print(last.parent, node)
+            refname = last["names"][0]
+            refid = last["ids"][0]
+
+            # Propagate the previous target
+            # Source from `PropagateTargets.apply`
+            node["ids"].extend(last["ids"])
+            node["names"].extend(last["names"])
+            # Set defaults for node.expect_referenced_by_name/id.
+            if not hasattr(node, "expect_referenced_by_name"):
+                node.expect_referenced_by_name = {}
+            if not hasattr(node, "expect_referenced_by_id"):
+                node.expect_referenced_by_id = {}
+            for id_ in last["ids"]:
+                node.expect_referenced_by_id[id_] = last
+                # Update IDs to node mapping.
+                self.document.ids[id_] = node
+            last["ids"] = []
+            for name in last["names"]:
+                node.expect_referenced_by_name[name] = last
+            last["names"] = []
+            # If there are any expect_referenced_by_name/id attributes in
+            # target set, copy them to node.
+            node.expect_referenced_by_name.update(
+                getattr(last, "expect_referenced_by_name", {}))
+            node.expect_referenced_by_id.update(
+                getattr(last, "expect_referenced_by_id", {}))
+            # Set refid to point to the first former ID of target which is now
+            # an ID of next_node.
+            last["refid"] = refid
+            self.document.note_refid(last)
+            # End source
+
             # Prefer the target's ID
             node["ids"].remove(refid)
             node["ids"].insert(0, refid)
+            # Also prefer the target's name
+            node["names"].remove(refname)
+            node["names"].insert(0, refname)
 
 def setup(app):
     """Sphinx extension entry point"""