Cache doctrees between reading and writing phases

sphinx/builders/__init__.py

@@ -542,6 +542,8 @@ class Builder:
         with open(doctree_filename, 'wb') as f:
             pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL)
 
+        self.env._write_doc_doctree_cache[docname] = doctree
+
     def write(
         self,
         build_docnames: Iterable[str],

sphinx/environment/__init__.py

@@ -181,6 +181,9 @@ class BuildEnvironment:
         # docname -> pickled doctree
         self._pickled_doctree_cache: dict[str, bytes] = {}
 
+        # docname -> doctree
+        self._write_doc_doctree_cache: dict[str, nodes.document] = {}
+
         # File metadata
         # docname -> dict of metadata items
         self.metadata: dict[str, dict[str, Any]] = defaultdict(dict)
@@ -608,7 +611,12 @@ class BuildEnvironment:
         toctrees and return it.
         """
         if doctree is None:
-            doctree = self.get_doctree(docname)
+            try:
+                doctree = self._write_doc_doctree_cache.pop(docname)
+                doctree.settings.env = self
+                doctree.reporter = LoggingReporter(self.doc2path(docname))
+            except KeyError:
+                doctree = self.get_doctree(docname)
 
         # resolve all pending cross-references
         self.apply_post_transforms(doctree, docname)