add diff style check test (#617)

* add diff style check test

* add diff style check test

* add diff style check test

* add diff style check test

* add license

* add license

tests/test_diff_codestyle.py

@@ -0,0 +1,115 @@
+"""
+Diff based code style checker with flake8
+
+This code come from:
+https://github.com/scipy/scipy/blob/main/tools/lint_diff.py
+
+Scipy's licence: https://github.com/scipy/scipy/blob/main/LICENSE.txt
+Copyright (c) 2001-2002 Enthought, Inc. 2003-2022, SciPy Developers.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above
+   copyright notice, this list of conditions and the following
+   disclaimer in the documentation and/or other materials provided
+   with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived
+   from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+"""
+import conftest
+import subprocess
+
+
+def rev_list(branch, num_commits):
+    """List commits in reverse chronological order.
+    Only the first `num_commits` are shown.
+    """
+    res = subprocess.run(
+        [
+            'git',
+            'rev-list',
+            '--max-count',
+            f'{num_commits}',
+            '--first-parent',
+            branch
+        ],
+        stdout=subprocess.PIPE,
+        encoding='utf-8',
+    )
+    res.check_returncode()
+    return res.stdout.rstrip('\n').split('\n')
+
+
+def find_branch_point(branch):
+    """Find when the current branch split off from the given branch.
+    It is based off of this Stackoverflow post:
+    https://stackoverflow.com/questions/1527234/finding-a-branch-point-with-git#4991675
+    """
+    branch_commits = rev_list('HEAD', 1000)
+    main_commits = set(rev_list(branch, 1000))
+    for branch_commit in branch_commits:
+        if branch_commit in main_commits:
+            return branch_commit
+
+    # If a branch split off over 1000 commits ago we will fail to find
+    # the ancestor.
+    raise RuntimeError(
+        'Failed to find a common ancestor in the last 1000 commits')
+
+
+def find_diff(sha):
+    """Find the diff since the given sha."""
+    files = ['*.py']
+    res = subprocess.run(
+        ['git', 'diff', '--unified=0', sha, '--'] + files,
+        stdout=subprocess.PIPE,
+        encoding='utf-8'
+    )
+    res.check_returncode()
+    return res.stdout
+
+
+def run_flake8(diff):
+    """Run flake8 on the given diff."""
+    res = subprocess.run(
+        ['flake8', '--diff'],
+        input=diff,
+        stdout=subprocess.PIPE,
+        encoding='utf-8',
+    )
+    return res.returncode, res.stdout
+
+
+def test():
+    branch_commit = find_branch_point("origin/master")
+    diff = find_diff(branch_commit)
+    rc, errors = run_flake8(diff)
+    if errors:
+        print(errors)
+    else:
+        print("No lint errors found.")
+    assert rc == 0
+
+
+if __name__ == '__main__':
+    conftest.run_this_test(__file__)