rebase: add --fail-fast support

Lets switch the default rebase behavior to align with our new sync
behavior: we try to rebase all projects by default and exit/summarize
things at the very end if there were any errors.  Or if people want
to exit immediately, they can use the new --fail-fast option.

Change-Id: I436ac563f972b45de6ce9ad74da1e4870e584902
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/238553
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

subcmds/rebase.py

@@ -37,6 +37,9 @@ branch but need to incorporate new upstream changes "underneath" them.
                 dest="interactive", action="store_true",
                 help="interactive rebase (single project only)")
 
+    p.add_option('--fail-fast',
+                 dest='fail_fast', action='store_true',
+                 help='Stop rebasing after first error is hit')
     p.add_option('-f', '--force-rebase',
                  dest='force_rebase', action='store_true',
                  help='Pass --force-rebase to git rebase')
@@ -88,7 +91,11 @@ branch but need to incorporate new upstream changes "underneath" them.
     if opt.interactive:
       common_args.append('-i')
 
+    ret = 0
     for project in all_projects:
+      if ret and opt.fail_fast:
+        break
+
       cb = project.CurrentBranch
       if not cb:
         if one_project:
@@ -127,13 +134,19 @@ branch but need to incorporate new upstream changes "underneath" them.
           stash_args = ["stash"]
 
           if GitCommand(project, stash_args).Wait() != 0:
-            return 1
+            ret += 1
+            continue
 
       if GitCommand(project, args).Wait() != 0:
-        return 1
+        ret += 1
+        continue
 
       if needs_stash:
         stash_args.append('pop')
         stash_args.append('--quiet')
         if GitCommand(project, stash_args).Wait() != 0:
-          return 1
+          ret += 1
+
+    if ret:
+      print('error: %i projects had errors' % (ret,), file=sys.stderr)
+    return ret