Do not try to fetch default revision for mirrors always

* Mirrors may contain multiple projects, some of which may not
  always contain the default revision.
* Only fetch the default revision explicitly if
  '--current-branch' is set.
* Fixes breakage casued by
  commit 6856f98467
  "Fix repo mirror with --current-branch"

Bug: https://crbug.com/gerrit/12274
Change-Id: Iaafabe2992f76f3644b841f24245d3e19c9515a9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/253093
Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Chirayu Desai <chirayudesai1@gmail.com>
(cherry picked from commit f7b64e3350)

project.py

@@ -2252,7 +2252,10 @@ class Project(object):
       spec.append('tag')
       spec.append(tag_name)
 
-    branch = self.revisionExpr
+    if self.manifest.IsMirror and not current_branch_only:
+      branch = None
+    else:
+      branch = self.revisionExpr
     if (not self.manifest.IsMirror and is_sha1 and depth
         and git_require((1, 8, 3))):
       # Shallow checkout of a specific commit, fetch from that commit and not

repo

@@ -16,7 +16,7 @@ import os
 REPO_URL = os.environ.get('REPO_URL', None)
 if not REPO_URL:
   REPO_URL = 'https://gerrit.googlesource.com/git-repo'
-REPO_REV = 'stable'
+REPO_REV = 'repo-1'
 
 # Copyright (C) 2008 Google Inc.
 #

subcmds/gitc_init.py

@@ -50,7 +50,7 @@ use for this GITC client.
 """
 
   def _Options(self, p):
-    super(GitcInit, self)._Options(p)
+    super(GitcInit, self)._Options(p, gitc_init=True)
     g = p.add_option_group('GITC options')
     g.add_option('-f', '--manifest-file',
                  dest='manifest_file',

subcmds/init.py

@@ -81,7 +81,7 @@ manifest, a subsequent `repo sync` (or `repo sync -d`) is necessary
 to update the working directory files.
 """
 
-  def _Options(self, p):
+  def _Options(self, p, gitc_init=False):
     # Logging
     g = p.add_option_group('Logging options')
     g.add_option('-q', '--quiet',
@@ -96,7 +96,12 @@ to update the working directory files.
     g.add_option('-b', '--manifest-branch',
                  dest='manifest_branch',
                  help='manifest branch or revision', metavar='REVISION')
-    g.add_option('-c', '--current-branch',
+    cbr_opts = ['--current-branch']
+    # The gitc-init subcommand allocates -c itself, but a lot of init users
+    # want -c, so try to satisfy both as best we can.
+    if gitc_init:
+      cbr_opts += ['-c']
+    g.add_option(*cbr_opts,
                  dest='current_branch_only', action='store_true',
                  help='fetch only current manifest branch from server')
     g.add_option('-m', '--manifest-name',