Add a script that allows developers to run checkstyle.

Allow developers to run Java style check in two ways.

Specific file:
checkstyle.py -f path/to/file/View.java

Lines modified in the latest commit:
checkstyle.py

Review moved from https://googleplex-android-review.googlesource.com/#/c/818813/
due to move from packages/experimental to development/tools

Bug: 25852971
Change-Id: Ibcf9d80644f2938828b21e8f50ab0d6f39c286b0

tools/checkstyle/gitlint/git.py

@@ -0,0 +1,139 @@
+# Copyright 2013-2014 Sebastian Kreft
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Functions to get information from git."""
+
+import os.path
+import subprocess
+
+import gitlint.utils as utils
+
+
+def repository_root():
+    """Returns the root of the repository as an absolute path."""
+    try:
+        root = subprocess.check_output(['git', 'rev-parse', '--show-toplevel'],
+                                       stderr=subprocess.STDOUT).strip()
+        # Convert to unicode first
+        return root.decode('utf-8')
+    except subprocess.CalledProcessError:
+        return None
+
+
+def last_commit():
+    """Returns the SHA1 of the last commit."""
+    try:
+        root = subprocess.check_output(['git', 'rev-parse', 'HEAD'],
+                                       stderr=subprocess.STDOUT).strip()
+        # Convert to unicode first
+        return root.decode('utf-8')
+    except subprocess.CalledProcessError:
+        return None
+
+
+def _remove_filename_quotes(filename):
+    """Removes the quotes from a filename returned by git status."""
+    if filename.startswith('"') and filename.endswith('"'):
+        return filename[1:-1]
+
+    return filename
+
+
+def modified_files(root, tracked_only=False, commit=None):
+    """Returns a list of files that has been modified since the last commit.
+
+    Args:
+      root: the root of the repository, it has to be an absolute path.
+      tracked_only: exclude untracked files when True.
+      commit: SHA1 of the commit. If None, it will get the modified files in the
+        working copy.
+
+    Returns: a dictionary with the modified files as keys, and additional
+      information as value. In this case it adds the status returned by
+      git status.
+    """
+    assert os.path.isabs(root), "Root has to be absolute, got: %s" % root
+
+    if commit:
+        return _modified_files_with_commit(root, commit)
+
+    # Convert to unicode and split
+    status_lines = subprocess.check_output([
+        'git', 'status', '--porcelain', '--untracked-files=all',
+        '--ignore-submodules=all']).decode('utf-8').split(os.linesep)
+
+    modes = ['M ', ' M', 'A ', 'AM', 'MM']
+    if not tracked_only:
+        modes.append(r'\?\?')
+    modes_str = '|'.join(modes)
+
+    modified_file_status = utils.filter_lines(
+        status_lines,
+        r'(?P<mode>%s) (?P<filename>.+)' % modes_str,
+        groups=('filename', 'mode'))
+
+    return dict((os.path.join(root, _remove_filename_quotes(filename)), mode)
+                for filename, mode in modified_file_status)
+
+
+def _modified_files_with_commit(root, commit):
+    # Convert to unicode and split
+    status_lines = subprocess.check_output(
+        ['git', 'diff-tree', '-r', '--root', '--no-commit-id', '--name-status',
+         commit]).decode('utf-8').split(os.linesep)
+
+    modified_file_status = utils.filter_lines(
+        status_lines,
+        r'(?P<mode>A|M)\s(?P<filename>.+)',
+        groups=('filename', 'mode'))
+
+    # We need to add a space to the mode, so to be compatible with the output
+    # generated by modified files.
+    return dict((os.path.join(root, _remove_filename_quotes(filename)),
+                 mode + ' ') for filename, mode in modified_file_status)
+
+
+def modified_lines(filename, extra_data, commit=None):
+    """Returns the lines that have been modifed for this file.
+
+    Args:
+      filename: the file to check.
+      extra_data: is the extra_data returned by modified_files. Additionally, a
+        value of None means that the file was not modified.
+      commit: the complete sha1 (40 chars) of the commit. Note that specifying
+        this value will only work (100%) when commit == last_commit (with
+        respect to the currently checked out revision), otherwise, we could miss
+        some lines.
+
+    Returns: a list of lines that were modified, or None in case all lines are
+      new.
+    """
+    if extra_data is None:
+        return []
+    if extra_data not in ('M ', ' M', 'MM'):
+        return None
+
+    if commit is None:
+        commit = '0' * 40
+    commit = commit.encode('utf-8')
+
+    # Split as bytes, as the output may have some non unicode characters.
+    blame_lines = subprocess.check_output(
+        ['git', 'blame', '--porcelain', filename]).split(
+            os.linesep.encode('utf-8'))
+    modified_line_numbers = utils.filter_lines(
+        blame_lines,
+        commit + br' (?P<line>\d+) (\d+)',
+        groups=('line',))
+
+    return list(map(int, modified_line_numbers))