revlogutils: teach issue6528 filtering about grandparents

During dynamic filtering, we should assume that the current repository
is correct. Therefore the parents of the delta base can tell us if that
parent has metadata without having to build the whole text.

mercurial/revlogutils/rewrite.py

@@ -618,12 +618,17 def _is_revision_affected_fast(repo, fl,
     delta = lambda: rl._inner._chunk(filerev)
     full_text = lambda: rl.rawdata(filerev)
     parent_revs = lambda: rl.parentrevs(filerev)
+    # This function is used by repair_issue6528, but not by
+    # filter_delta_issue6528. As such, we do not want to trust
+    # parent revisions of the delta base to decide whether
+    # the delta base has metadata.
     return _is_revision_affected_fast_inner(
         is_censored,
         delta_base,
         delta,
         full_text,
         parent_revs,
+        None,  # don't trust the parent revisions
         filerev,
         metadata_cache,
     )
@@ -635,6 +640,7 def _is_revision_affected_fast_inner(
     delta,
     full_text,
     parent_revs,
+    deltabase_parentrevs,
     filerev,
     metadata_cache,
 ):
@@ -659,12 +665,25 def _is_revision_affected_fast_inner(
     delta_parent = delta_base()
     parent_has_metadata = metadata_cache.get(delta_parent)
     if parent_has_metadata is None:
-        return _is_revision_affected_inner(
-            full_text,
-            parent_revs,
-            filerev,
-            metadata_cache,
-        )
+        if deltabase_parentrevs is not None:
+            deltabase_parentrevs = deltabase_parentrevs()
+            if deltabase_parentrevs == (nullrev, nullrev):
+                # Need to check the content itself as there is no flag.
+                parent_has_metadata = None
+            elif deltabase_parentrevs[0] == nullrev:
+                # Second parent is !null, assume repository is correct
+                # and has flagged this file revision as having metadata.
+                parent_has_metadata = True
+            elif deltabase_parentrevs[1] == nullrev:
+                # First parent is !null, so assume it has no metadata.
+                parent_has_metadata = False
+        if parent_has_metadata is None:
+            return _is_revision_affected_inner(
+                full_text,
+                parent_revs,
+                filerev,
+                metadata_cache,
+            )
 
     chunk = delta()
     if not len(chunk):
@@ -766,9 +785,9 def filter_delta_issue6528(revlog, delta
         p2_rev = revlog.rev(p2_node)
 
         is_censored = lambda: bool(flags & REVIDX_ISCENSORED)
-        delta_base = lambda: revlog.rev(delta_base)
         delta_base = lambda: base_rev
         parent_revs = lambda: (p1_rev, p2_rev)
+        deltabase_parentrevs = lambda: revlog.parentrevs(base_rev)
 
         def full_text():
             # note: being able to reuse the full text computation in the
@@ -794,6 +813,7 def filter_delta_issue6528(revlog, delta
             lambda: delta,
             full_text,
             parent_revs,
+            deltabase_parentrevs,
             rev,
             metadata_cache,
         )