Use new common tools in Python scripts

tools/git_utils.py

-# 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
-
-import misc_utils
-
-
-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():
-            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:
-        branch_name: (string) if not None, the name of the branch to
-            use.  If None, then use a temporary branch that will be
-            deleted.  If the branch already exists, then a different
-            branch name will be created.  Use git_branch_name() to
-            find the actual branch name used.
-        upstream_branch: (string) if not None, the name of the branch or
-            commit to branch from.  If None, then use origin/master
-        verbose: (boolean) if true, makes debugging easier.
-
-    Raises:
-        OSError: the git executable disappeared.
-        subprocess.CalledProcessError: git returned unexpected status.
-        Exception: if the given branch name exists, or if the repository
-            isn't clean on exit, or git can't be found.
-    """
-    # pylint: disable=I0011,R0903,R0902
-
-    def __init__(self,
-                 branch_name=None,
-                 upstream_branch=None,
-                 verbose=False):
-        # pylint: disable=I0011,R0913
-        if branch_name:
-            self._branch_name = branch_name
-            self._delete_branch = False
-        else:
-            self._branch_name = 'ChangeGitBranchTempBranch'
-            self._delete_branch = True
-
-        if upstream_branch:
-            self._upstream_branch = upstream_branch
-        else:
-            self._upstream_branch = 'origin/master'
-
-        self._git = git_executable()
-        if not self._git:
-            raise Exception('Git can\'t be found.')
-
-        self._stash = None
-        self._original_branch = None
-        self._vsp = misc_utils.VerboseSubprocess(verbose)
-
-    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
-
-        if self._branch_exists(self._branch_name):
-            i, branch_name = 0, self._branch_name
-            while self._branch_exists(branch_name):
-                i += 1
-                branch_name = '%s_%03d' % (self._branch_name, i)
-            self._branch_name = branch_name
-
-        self._stash = self._has_git_diff()
-        if self._stash:
-            vsp.check_call([git, 'stash', 'save'])
-        self._original_branch = git_branch_name(vsp.verbose)
-        vsp.check_call(
-            [git, 'checkout', '-q', '-b',
-             self._branch_name, self._upstream_branch])
-
-    def __exit__(self, etype, value, traceback):
-        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(verbose=False):
-    """Return a description of the current branch.
-
-    Args:
-        verbose: (boolean) makes debugging easier
-
-    Returns:
-        A string suitable for passing to `git checkout` later.
-    """
-    git = git_executable()
-    vsp = misc_utils.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):
-    """Test the git executable.
-
-    Args:
-        git: git executable path.
-    Returns:
-        True if test is successful.
-    """
-    with open(os.devnull, 'w') as devnull:
-        try:
-            subprocess.call([git, '--version'], stdout=devnull)
-        except (OSError,):
-            return False
-    return True
-
-
-def git_executable():
-    """Find the git executable.
-
-    If the GIT_EXECUTABLE environment variable is set, that will
-    override whatever is found in the PATH.
-
-    If no suitable executable is found, return None
-
-    Returns:
-        A string suiable for passing to subprocess functions, or None.
-    """
-    env_git = os.environ.get('GIT_EXECUTABLE')
-    if env_git and test_git_executable(env_git):
-        return env_git
-    for git in ('git', 'git.exe', 'git.bat'):
-        if test_git_executable(git):
-            return git
-    return None
-