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tools/git_utils.py

Index: tools/git_utils.py
diff --git a/tools/git_utils.py b/tools/git_utils.py
new file mode 100644
index 0000000000000000000000000000000000000000..910dc47a7086942e996dc1cbeef2999d5c11d9df
--- /dev/null
+++ b/tools/git_utils.py
@@ -0,0 +1,136 @@
+# Copyright 2014 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Module to host the ChangeGitBranch class and test_git_executable function.
+"""
+
+import os
+import subprocess
+from misc_utils import VerboseSubprocess
+
+
+class ChangeGitBranch(object):
+    """Class to manage git branches.
+
+    This class allows one to create a new branch in a repository based
+    off of a given commit, and restore the original tree state.
+
+    Assumes current working directory is a git repository.
+
+    Example:
+        with ChangeGitBranch('git', 'newBranch'):
+            edit_files(files)
+            git_add(files)
+            git_commit()
+            git_format_patch('HEAD~')
+        # At this point, the repository is returned to its original
+        # state.
+
+    Constructor Args:
+        git: (string) git executable.
+        brach_name: (string) if not None, the name of the branch to

[borenet, 2014/01/30 14:36:35]

"branch_name".

Also, please document that this exact name might not be used if the branch
already exists.

[hal.canary, 2014/01/30 20:11:02]

Done.

+            use.  If None, then use a temporary branch that will be
+            deleted.
+        start_point: (string) if not None, the name of the branch or
+            commit to branch from.  If None, then use origin/master

[borenet, 2014/01/30 14:36:35]

I think upstream_branch or tracking_branch are better names for this.

[hal.canary, 2014/01/30 20:11:02]

Done.

+        verbose: (boolean) if true, makes debugging easier.
+        delete_branch: (boolean) delete the branch afterwards
+
+    Raises:
+        OSError: failed to execute git.
+        subprocess.CalledProcessError: git returned unexpected status.
+        Exception: if the given branch name exists, or if the repository
+            isn't clean on exit
+    """
+    # pylint: disable=I0011,R0903,R0902
+
+    def __init__(self,
+                 git,
+                 branch_name,
+                 start_point=None,
+                 verbose=False,
+                 delete_branch=False):
+        # pylint: disable=I0011,R0913
+        self._branch_name = branch_name
+        if start_point:
+            self._start_point = start_point
+        else:
+            self._start_point = 'origin/master'
+        self._git = git
+        self._stash = None
+        self._original_branch = None
+        self._vsp = VerboseSubprocess(verbose)
+        self._delete_branch = delete_branch
+
+    def _has_git_diff(self):
+        """Return true iff repository has uncommited changes."""
+        return bool(self._vsp.call([self._git, 'diff', '--quiet', 'HEAD']))
+
+    def _branch_exists(self, branch):
+        """Return true iff branch exists."""
+        return 0 == self._vsp.call([self._git, 'show-ref', '--quiet', branch])
+
+    def __enter__(self):
+        git, vsp = self._git, self._vsp
+
+        while self._branch_exists(self._branch_name):
+            self._branch_name += '_'
+
+        self._stash = self._has_git_diff()
+        if self._stash:
+            vsp.check_call([git, 'stash', 'save'])
+        self._original_branch = git_branch_name(git, vsp.verbose)
+        vsp.check_call(
+            [git, 'checkout', '-q', '-b',
+             self._branch_name, self._start_point])
+
+    def __exit__(self, etype, value, traceback):
+        # pylint: disable=I0011,R0912
+        git, vsp = self._git, self._vsp
+
+        if self._has_git_diff():
+            status = vsp.check_output([git, 'status', '-s'])
+            raise Exception('git checkout not clean:\n%s' % status)
+        vsp.check_call([git, 'checkout', '-q', self._original_branch])
+        if self._stash:
+            vsp.check_call([git, 'stash', 'pop'])
+        if self._delete_branch:
+            assert self._original_branch != self._branch_name
+            vsp.check_call([git, 'branch', '-D', self._branch_name])
+
+
+def git_branch_name(git, verbose):
+    """Return a description of the current branch.
+
+    Args:
+        git: (string) git executable.
+        verbose: (boolean) makes debugging easier
+
+    Returns:
+        A string suitable for passing to `git checkout` later.
+    """
+    vsp = VerboseSubprocess(verbose)
+    try:
+        full_branch = vsp.strip_output([git, 'symbolic-ref', 'HEAD'])
+        return full_branch.split('/')[-1]
+    except (subprocess.CalledProcessError,):
+        # "fatal: ref HEAD is not a symbolic ref"
+        return vsp.strip_output([git, 'rev-parse', 'HEAD'])
+
+
+def test_git_executable(git_executable):
+    """Test the git executable.
+
+    Args:
+        git_executable: git executable path.
+    Returns:
+        True if test is successful.
+    """
+    with open(os.devnull, 'w') as devnull:
+        try:
+            subprocess.call([git_executable, '--version'], stdout=devnull)
+        except (OSError,):
+            return False
+    return True