repo: lower min version of git a bit

We were perhaps a bit too hasty to jump to git-2.10.  Existing LTS
releases of Ubuntu are quite old still: Trusty has 1.9 while Xenial
has 2.5.  While we plan on dropping support for those eventually as
we migrate to Python 3.6, we don't need to be so strict just yet on
the git versions.

We also want to disconnect the version the repo launcher requires
from the version the rest of the source tree requires.  The repo
launcher doesn't need as many features, and being flexible there
allows us more freedom to upgrade & rollback as needed.

So we'll allow git-1.7 again, but start warning on any users older
than git-1.9.  This aligns better with existing LTS releases, and
gives users a chance to start upgrading before we cut them off.

Change-Id: I140305dd8e42c9719c84e2aee0dc6a5c5b18da25
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254573
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

git_command.py

@@ -28,8 +28,17 @@ from repo_trace import REPO_TRACE, IsTrace, Trace
 from wrapper import Wrapper
 
 GIT = 'git'
-# Should keep in sync with the "repo" launcher file.
+# NB: These do not need to be kept in sync with the repo launcher script.
-MIN_GIT_VERSION = (2, 10, 2)
+# These may be much newer as it allows the repo launcher to roll between
+# different repo releases while source versions might require a newer git.
+#
+# The soft version is when we start warning users that the version is old and
+# we'll be dropping support for it.  We'll refuse to work with versions older
+# than the hard version.
+#
+# git-1.7 is in (EOL) Ubuntu Precise.  git-1.9 is in Ubuntu Trusty.
+MIN_GIT_VERSION_SOFT = (1, 9, 1)
+MIN_GIT_VERSION_HARD = (1, 7, 2)
 GIT_DIR = 'GIT_DIR'
 
 LAST_GITDIR = None

repo

@@ -166,7 +166,12 @@ TACbBS+Up3RpfYVfd63c1cDdlru13pQAn3NQy/SN858MkxN+zym86UBgOad2
 """
 
 GIT = 'git'                      # our git command
-MIN_GIT_VERSION = (2, 10, 2)     # minimum supported git version
+# NB: The version of git that the repo launcher requires may be much older than
+# the version of git that the main repo source tree requires.  Keeping this at
+# an older version also makes it easier for users to upgrade/rollback as needed.
+#
+# git-1.7 is in (EOL) Ubuntu Precise.
+MIN_GIT_VERSION = (1, 7, 2)      # minimum supported git version
 repodir = '.repo'                # name of repo's private directory
 S_repo = 'repo'                  # special repo repository
 S_manifests = 'manifests'        # special manifest repository

subcmds/init.py

@@ -34,7 +34,7 @@ from command import InteractiveCommand, MirrorSafeCommand
 from error import ManifestParseError
 from project import SyncBuffer
 from git_config import GitConfig
-from git_command import git_require, MIN_GIT_VERSION
+from git_command import git_require, MIN_GIT_VERSION_SOFT, MIN_GIT_VERSION_HARD
 import platform_utils
 
 class Init(InteractiveCommand, MirrorSafeCommand):
@@ -451,7 +451,12 @@ to update the working directory files.
       self.OptionParser.error('--mirror and --archive cannot be used together.')
 
   def Execute(self, opt, args):
-    git_require(MIN_GIT_VERSION, fail=True)
+    git_require(MIN_GIT_VERSION_HARD, fail=True)
+    if not git_require(MIN_GIT_VERSION_SOFT):
+      print('repo: warning: git-%s+ will soon be required; please upgrade your '
+            'version of git to maintain support.'
+            % ('.'.join(str(x) for x in MIN_GIT_VERSION_SOFT),),
+            file=sys.stderr)
 
     self._SyncManifest(opt)
     self._LinkManifest(opt.manifest_name)