repo: skip invalidation of changelog if it has 'delayed' changes (API)

The changelog object can store recently added revisions in memory
until the transaction is committed. We don't want to lose those
changes even if repo.invalidate(clearfilecache=True), so let's skip
the changelog when it has such 'delayed' changes.

Differential Revision: https://phab.mercurial-scm.org/D152

mercurial/localrepo.py

@@ -1461,6 +1461,13 b' class localrepository(object):'
             # dirstate is invalidated separately in invalidatedirstate()
             if k == 'dirstate':
                 continue
+            if (k == 'changelog' and
+                self.currenttransaction() and
+                self.changelog._delayed):
+                # The changelog object may store unwritten revisions. We don't
+                # want to lose them.
+                # TODO: Solve the problem instead of working around it.
+                continue
 
             if clearfilecache:
                 del self._filecache[k]

tests/test-context.py

@@ -179,3 +179,14 b" for i in [b'1', b'2', b'3']:"
             print('data mismatch')
     except Exception as ex:
         print('cannot read data: %r' % ex)
+
+with repo.wlock(), repo.lock(), repo.transaction('test'):
+    with open(b'4', 'wb') as f:
+        f.write(b'4')
+    repo.dirstate.normal('4')
+    repo.commit('4')
+    revsbefore = len(repo.changelog)
+    repo.invalidate(clearfilecache=True)
+    revsafter = len(repo.changelog)
+    if revsbefore != revsafter:
+        print('changeset lost by repo.invalidate()')