git: Update git submodules with --checkout

Git 1.7.8 and newer allows submodules to be updated by other commands
than "git checkout". When this behavior is configured in .gitmodules,
buildbot can end up with incorrect commit checked out in the submodule.

Fix this by explicitly specifying --checkout option to "git submodule
update".

master/buildbot/steps/source/git.py

@@ -125,6 +125,7 @@ def __init__(self, repourl=None, branch='HEAD', mode='incremental', method=None,
         self.getDescription = getDescription
         self.config = config
         self.supportsBranch = True
+        self.supportsSubmoduleCheckout = True
         self.srcdir = 'source'
         Source.__init__(self, **kwargs)
 
@@ -534,8 +535,10 @@ def _syncSubmodule(self, _=None):
 
     def _updateSubmodule(self, _=None):
         if self.submodules:
-            return self._dovccmd(['submodule', 'update',
-                                  '--init', '--recursive', '--force'])
+            vccmd = ['submodule', 'update', '--init', '--recursive', '--force']
+            if self.supportsSubmoduleCheckout:
+                vccmd.extend(['--checkout'])
+            return self._dovccmd(vccmd)
         else:
             return defer.succeed(0)
 
@@ -567,6 +570,8 @@ def checkSupport(stdout):
             version = stdout.strip().split(' ')[2]
             if LooseVersion(version) < LooseVersion("1.6.5"):
                 self.supportsBranch = False
+            if LooseVersion(version) < LooseVersion("1.7.8"):
+                self.supportsSubmoduleCheckout = False
             return gitInstalled
         return d
 

master/buildbot/test/unit/test_steps_source_git.py

@@ -950,6 +950,56 @@ def test_mode_full_fresh_submodule(self):
         self.expectProperty('got_revision', 'f6ad368298bd941e934a41f3babc827b2aa95a1d', 'Git')
         return self.runStep()
 
+    def test_mode_full_fresh_submodule_v1_7_8(self):
+        """This tests the same as test_mode_full_fresh_submodule, but the
+        "submodule update" command should be different for Git v1.7.8+."""
+        self.setupStep(
+            git.Git(repourl='http://github.com/buildbot/buildbot.git',
+                    mode='full', method='fresh', submodules=True))
+        self.expectCommands(
+            ExpectShell(workdir='wkdir',
+                        command=['git', '--version'])
+            + ExpectShell.log('stdio',
+                              stdout='git version 1.7.8')
+            + 0,
+            Expect('stat', dict(file='wkdir/.buildbot-patched',
+                                logEnviron=True))
+            + 1,
+            Expect('listdir', {'dir': 'wkdir', 'logEnviron': True,
+                               'timeout': 1200})
+            + Expect.update('files', ['.git'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'clean', '-f', '-f', '-d', '-x'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'fetch', '-t',
+                                 'http://github.com/buildbot/buildbot.git',
+                                 'HEAD'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'reset', '--hard', 'FETCH_HEAD', '--'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'submodule', 'sync'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'submodule', 'update', '--init', '--recursive', '--force', '--checkout'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'submodule', 'foreach', '--recursive', 'git', 'clean',
+                                 '-f', '-f', '-d', '-x'])
+            + 0,
+            ExpectShell(workdir='wkdir',
+                        command=['git', 'rev-parse', 'HEAD'])
+            + ExpectShell.log('stdio',
+                              stdout='f6ad368298bd941e934a41f3babc827b2aa95a1d')
+            + 0,
+        )
+        self.expectOutcome(result=SUCCESS)
+        self.expectProperty('got_revision', 'f6ad368298bd941e934a41f3babc827b2aa95a1d', 'Git')
+        return self.runStep()
+
     def test_mode_full_clobber_shallow(self):
         self.setupStep(
             git.Git(repourl='http://github.com/buildbot/buildbot.git',