From patchwork Wed Mar 10 17:10:03 2021
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Subject: D10150: revlog: guarantee that p1 != null if a non-null parent exists
From: phabricator <phabricator@mercurial-scm.org>
X-Patchwork-Id: 48465
Message-Id: <differential-rev-PHID-DREV-b6huestsah5tdgbipv5v-req@mercurial-scm.org>
To: Phabricator <phabricator@mercurial-scm.org>
Cc: mercurial-devel@mercurial-scm.org
Date: Wed, 10 Mar 2021 17:10:03 +0000

joerg.sonnenberger created this revision.
Herald added a reviewer: indygreg.
Herald added a reviewer: durin42.
Herald added a reviewer: hg-reviewers.
Herald added a subscriber: mercurial-patches.

REVISION SUMMARY
  This change does not affect the hashing (which already did this
  transformation), but can change the log output in the rare case where
  this behavior was observed in repositories. The change can simplify
  iteration code where regular changesets and merges are distinct
  branches.

REPOSITORY
  rHG Mercurial

BRANCH
  default

REVISION DETAIL
  https://phab.mercurial-scm.org/D10150

AFFECTED FILES
  mercurial/revlog.py
  relnotes/next
  tests/test-narrow-shallow-merges.t

CHANGE DETAILS




To: joerg.sonnenberger, indygreg, durin42, #hg-reviewers
Cc: mercurial-patches, mercurial-devel

diff --git a/tests/test-narrow-shallow-merges.t b/tests/test-narrow-shallow-merges.t
--- a/tests/test-narrow-shallow-merges.t
+++ b/tests/test-narrow-shallow-merges.t
@@ -179,7 +179,7 @@
   
 
   $ hg log -T '{if(ellipsis,"...")}{node|short} {p1node|short} {p2node|short} {desc}\n' | sort
-  ...2a20009de83e 000000000000 3ac1f5779de3 outside 10
+  ...2a20009de83e 3ac1f5779de3 000000000000 outside 10
   ...3ac1f5779de3 bb96a08b062a 465567bdfb2d merge a/b/c/d 9
   ...8d874d57adea 7ef88b4dd4fa 000000000000 outside 12
   ...b844052e7b3b 000000000000 000000000000 outside 2c
diff --git a/relnotes/next b/relnotes/next
--- a/relnotes/next
+++ b/relnotes/next
@@ -21,6 +21,13 @@
 
 == Backwards Compatibility Changes ==
 
+ * In normal repositories, the first parent of a changeset is not null,
+   unless both parents are null (like the first changeset). Some legacy
+   repositories violate this condition. The revlog code will now
+   silentely swap the parents if this condition is tested. This can
+   change the output of `hg log` when explicitly asking for first or
+   second parent.
+
 
 == Internal API Changes ==
 
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -878,8 +878,10 @@
             if rev == wdirrev:
                 raise error.WdirUnsupported
             raise
-
-        return entry[5], entry[6]
+        if entry[5] == nullrev:
+            return entry[6], entry[5]
+        else:
+            return entry[5], entry[6]
 
     # fast parentrevs(rev) where rev isn't filtered
     _uncheckedparentrevs = parentrevs
@@ -900,7 +902,11 @@
     def parents(self, node):
         i = self.index
         d = i[self.rev(node)]
-        return i[d[5]][7], i[d[6]][7]  # map revisions to nodes inline
+        # inline node() to avoid function call overhead
+        if d[5] == nullid:
+            return i[d[6]][7], i[d[5]][7]
+        else:
+            return i[d[5]][7], i[d[6]][7]
 
     def chainlen(self, rev):
         return self._chaininfo(rev)[0]