issue6528: implement _is_revision_affected using callback

The delta comming from a bundle/stream does not exists in the revlog yet, so we
will need other way to retrieve the same information.

To prepare for this we split the function to use callbacks in the core logic.

Differential Revision: https://phab.mercurial-scm.org/D11267

mercurial/revlogutils/rewrite.py

@@ -563,6 +563,19 b' def _reorder_filelog_parents(repo, fl, t'
 
 
 def _is_revision_affected(fl, filerev, metadata_cache=None):
+    full_text = lambda: fl._revlog.rawdata(filerev)
+    parent_revs = lambda: fl._revlog.parentrevs(filerev)
+    return _is_revision_affected_inner(
+        full_text, parent_revs, filerev, metadata_cache
+    )
+
+
+def _is_revision_affected_inner(
+    full_text,
+    parents_revs,
+    filerev,
+    metadata_cache=None,
+):
     """Mercurial currently (5.9rc0) uses `p1 == nullrev and p2 != nullrev` as a
     special meaning compared to the reverse in the context of filelog-based
     copytracing. issue6528 exists because new code assumed that parent ordering
@@ -570,7 +583,7 b' def _is_revision_affected(fl, filerev, m'
     it's only used for filelog-based copytracing) and its parents are in the
     "wrong" order."""
     try:
-        raw_text = fl.rawdata(filerev)
+        raw_text = full_text()
     except error.CensoredNodeError:
         # We don't care about censored nodes as they never carry metadata
         return False
@@ -578,7 +591,7 b' def _is_revision_affected(fl, filerev, m'
     if metadata_cache is not None:
         metadata_cache[filerev] = has_meta
     if has_meta:
-        (p1, p2) = fl.parentrevs(filerev)
+        (p1, p2) = parents_revs()
         if p1 != nullrev and p2 == nullrev:
             return True
     return False