--- a/autoland/autoland/transplant.py
+++ b/autoland/autoland/transplant.py
@@ -99,26 +99,30 @@ def _transplant(logger, client, tree, de
     if commit_descriptions:
         with tempfile.NamedTemporaryFile() as f:
             json.dump(commit_descriptions, f)
             f.flush()
 
             try:
                 cmd = ['rewritecommitdescriptions',
                        '--descriptions=%s' % f.name, rev]
-                base_revision = run_hg(cmd)
+                cmd_output = run_hg(cmd)
             except hglib.error.CommandError as e:
-                return False, formulate_hg_error(['hg'] + cmd, base_revision)
+                return False, formulate_hg_error(['hg'] + cmd, cmd_output)
 
-        m = re.search(r'base: ([0-9a-z]+)$', base_revision)
-        if not m or not m.groups():
+        for line in cmd_output.splitlines():
+            m = re.search(r'^rev: [0-9a-z]+ -> ([0-9a-z]+)', line)
+            if m and m.groups():
+                base_revision = m.groups()[0]
+                break
+
+        if not base_revision:
             return False, ('Could not determine base revision for rebase: ' +
-                           base_revision)
+                           cmd_output)
 
-        base_revision = m.groups()[0]
         logger.info('base revision: %s' % base_revision)
 
     if not trysyntax and not base_revision:
         return False, 'Could not determine base revision for rebase'
 
     # Perform rebase if necessary
     if not trysyntax:
         try:

--- a/autoland/hgext/rewritecommitdescriptions.py
+++ b/autoland/hgext/rewritecommitdescriptions.py
@@ -1,96 +1,106 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 import json
 import os
 
 from mercurial import (context,
                        cmdutil,
                        encoding,
+                       error,
+                       extensions,
                        phases)
 
-from mercurial.i18n import _
-
 OUR_DIR = os.path.normpath(os.path.dirname(__file__))
 execfile(os.path.join(OUR_DIR, '..', '..', 'hgext', 'bootstrap.py'))
 
 from mozhg import rewrite
 
 testedwith = '3.5'
 
 cmdtable = {}
 command = cmdutil.command(cmdtable)
 
 
 @command('rewritecommitdescriptions',
          [('', 'descriptions', '',
            'path to json file with new commit descriptions', 'string')],
-         _('hg rewritecommitdescriptions'))
-def rewrite_commit_descriptions(ui, repo, node, descriptions=None):
+         'hg rewritecommitdescriptions')
+def rewrite_commit_descriptions(ui, repo, base_node, descriptions=None):
+
+    def sha1_of(node):
+        return repo[node].hex()[:12]
 
+    # Rewriting fails if the evolve extension is enabled.
+    try:
+        extensions.find('evolve')
+        raise error.Abort('Cannot continue as the "evolve" extension is '
+                          'enabled.')
+    except KeyError:
+        pass
+
+    # Read commit descriptions map.
     description_map = {}
     with open(descriptions, 'rb') as f:
         raw_descriptions = json.load(f)
-        for k in raw_descriptions:
-            description_map[k[:12]] = encoding.tolocal(
-                raw_descriptions[k].encode('utf-8'))
+        for sha1 in raw_descriptions:
+            description_map[sha1[:12]] = encoding.tolocal(
+                raw_descriptions[sha1].encode('utf-8'))
+
+    # Collect nodes listed by description_map.
+    nodes = []
 
-    if not node:
-        node = 'tip'
+    def add_node(ctx):
+        node = ctx.node()
+        if sha1_of(node) in description_map:
+            nodes.append(node)
 
-    ctx = repo[node]
-    nodes = [ctx.node()]
+    ctx = repo[base_node]
+    add_node(ctx)
     for ancestor in ctx.ancestors():
-        ctx = repo[ancestor]
         if ctx.phase() != phases.draft:
             break
-        sha1 = repo[ctx.node()].hex()[:12]
-        if sha1 in description_map:
-            nodes.append(ctx.node())
+        add_node(repo[ancestor])
     nodes.reverse()
 
     if not nodes:
-        ui.write(_('no commits found to be rewritten\n'))
-        return 1
+        raise error.Abort('No commits found to be rewritten.')
 
-    oldest_relevant_commit = repo[nodes[0]].hex()[:12]
+    # We need to store the original sha1 values because we won't be able to
+    # look them up once they are rewritten.
+    original_sha1s = {}
+    for node in nodes:
+        original_sha1s[node] = sha1_of(node)
 
+    # Update changed nodes.
     def prune_unchanged(node):
-        sha1 = repo[node].hex()[:12]
-        description = repo[node].description()
-        revised_description = description_map.get(sha1, description)
-        if description == revised_description:
-            ui.write(_('not rewriting %s - description unchanged\n' % sha1))
-            return False
-        return True
+        return repo[node].description() != description_map[sha1_of(node)]
 
-    nodes = filter(prune_unchanged, nodes)
-    if not nodes:
-        ui.write(_('no commits found to be rewritten\n'))
-        # in this case, we need to output the sha1 of the oldest commit
-        # present in commit descriptions
-        ui.write('base: ' + oldest_relevant_commit + '\n')
-        return 0
-
-    def createfn(repo, ctx, revmap, filectxfn):
+    def create_func(repo, ctx, revmap, filectxfn):
         parents = rewrite.newparents(repo, ctx, revmap)
 
         sha1 = ctx.hex()[:12]
-        if sha1 in description_map:
-            description = description_map[sha1]
-        else:
-            description = ctx.description()
+        description = description_map[sha1]
 
         memctx = context.memctx(repo, parents, description,
                                 ctx.files(), filectxfn, user=ctx.user(),
                                 date=ctx.date(), extra=ctx.extra())
         status = ctx.p1().status(ctx)
         memctx.modified = lambda: status[0]
         memctx.added = lambda: status[1]
         memctx.removed = lambda: status[2]
 
         return memctx
 
-    # we output the sha1 of the oldest modified commit
-    nodemap = rewrite.replacechangesets(repo, nodes, createfn)
-    ui.write('base: ' + repo[nodemap[nodes[0]]].hex()[:12] + '\n')
-    return 0
+    node_map = {}
+    changed_nodes = filter(prune_unchanged, nodes)
+    if changed_nodes:
+        node_map = rewrite.replacechangesets(repo, changed_nodes, create_func)
+
+    # Output result.
+    for node in nodes:
+        original_sha1 = original_sha1s[node]
+        if node in node_map:
+            new_sha1 = sha1_of(node_map[node])
+        else:
+            new_sha1 = original_sha1s[node]
+        ui.write('rev: %s -> %s\n' % (original_sha1, new_sha1))

--- a/autoland/tests/test-rewritecommitdescriptions.t
+++ b/autoland/tests/test-rewritecommitdescriptions.t
@@ -21,19 +21,18 @@ Create some commits to rewrite
   $ REV=`hg log -r . --template "{node|short}"`
 
 We handle having no commits which match commit_descriptions properly
 
   $ cat > descriptions.json << EOF
   > {"42": "non-existent commit"}
   > EOF
   $ hg rewritecommitdescriptions --descriptions descriptions.json .
-  not rewriting 10f03055d22c - description unchanged
-  no commits found to be rewritten
-  base: 10f03055d22c
+  abort: No commits found to be rewritten.
+  [255]
   $ hg --encoding utf-8 log
   changeset:   2:10f03055d22c
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     bug 1 - more stuff
   
   changeset:   1:599eee383634
@@ -48,19 +47,17 @@ We handle having no commits which match 
   
 
 We handle having no commits to rewrite properly
 
   $ cat > descriptions.json << EOF
   > {"$REV": "bug 1 - more stuff"}
   > EOF
   $ hg rewritecommitdescriptions --descriptions descriptions.json .
-  not rewriting 10f03055d22c - description unchanged
-  no commits found to be rewritten
-  base: 10f03055d22c
+  rev: 10f03055d22c -> 10f03055d22c
   $ hg --encoding utf-8 log
   changeset:   2:10f03055d22c
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     bug 1 - more stuff
   
   changeset:   1:599eee383634
@@ -76,17 +73,18 @@ We handle having no commits to rewrite p
 
 We handle unicode commit descriptions properly
 
   $ cat > descriptions.json << EOF
   > {"$REV": "bug 1 - こんにちは", "$PARENT": "bug 1 - stuff++"}
   > EOF
   $ hg rewritecommitdescriptions --descriptions descriptions.json .
   saved backup bundle to $TESTTMP/clone/.hg/strip-backup/10f03055d22c-f5e0148f-replacing.hg (glob)
-  base: a1dea3050632
+  rev: 599eee383634 -> a1dea3050632
+  rev: 10f03055d22c -> 99d16379ed19
 
   $ hg --encoding utf-8 log
   changeset:   2:99d16379ed19
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     bug 1 - \xe3\x81\x93\xe3\x82\x93\xe3\x81\xab\xe3\x81\xa1\xe3\x81\xaf (esc)
   
@@ -104,17 +102,17 @@ We handle unicode commit descriptions pr
 We handle long sha1s properly
 
   $ REV=`hg log -r . --template "{node}"`
   $ cat > descriptions.json << EOF
   > {"$REV": "bug 1 - long sha1 is ok"}
   > EOF
   $ hg rewritecommitdescriptions --descriptions descriptions.json .
   saved backup bundle to $TESTTMP/clone/.hg/strip-backup/99d16379ed19-6e1da412-replacing.hg (glob)
-  base: 2c6f2ddf672a
+  rev: 99d16379ed19 -> 2c6f2ddf672a
 
   $ hg --encoding utf-8 log
   changeset:   2:2c6f2ddf672a
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     bug 1 - long sha1 is ok