transaction: track newly introduced revisions

Tracking revisions is not the data that will unlock the most new capability.
However, they are the simplest thing to track and still unlock some nice
improvements in regard with caching.

We plug ourself at the changelog level to make sure we do not miss any revision
additions.

The 'revs' set is configured at the repository level because the transaction
itself does not needs to know that much about the business logic.

mercurial/changelog.py

@@ -535,3 +535,14 b' class changelog(revlog.revlog):'
         just to access this is costly."""
         extra = self.read(rev)[5]
         return encoding.tolocal(extra.get("branch")), 'close' in extra
+
+    def _addrevision(self, node, rawtext, transaction, *args, **kwargs):
+        # overlay over the standard revlog._addrevision to track the new
+        # revision on the transaction.
+        rev = len(self)
+        node = super(changelog, self)._addrevision(node, rawtext, transaction,
+                                                   *args, **kwargs)
+        revs = transaction.changes.get('revs')
+        if revs is not None:
+            revs.add(rev)
+        return node

mercurial/localrepo.py

@@ -1072,6 +1072,7 b' class localrepository(object):'
                                      self.store.createmode,
                                      validator=validate,
                                      releasefn=releasefn)
+        tr.changes['revs'] = set()
 
         tr.hookargs['txnid'] = txnid
         # note: writing the fncache only during finalize mean that the file is