Add Python script for auto-generating changelogs from pull requests.

For more information, please see http://mattdeboard.net/2014/01/14/automatic-changelog-generation-with-git/.

Author: mattdeboard

release.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python
+"""This script generates release notes for each merged pull request from
+git merge-commit messages.
+
+Usage:
+
+ `python release.py <start_commit> <end_commit> [--output {file,stdout}]`
+
+For example, if you wanted to find the diff between version 1.0 and 1.2,
+and write the output to the release notes file, you would type the
+following:
+
+ `python release.py 1.0 1.2 -o file`
+
+"""
+import os.path as op
+import re
+import subprocess
+from collections import deque
+
+
+def commit_msgs(start_commit, end_commit):
+    """Run the git command that outputs the merge commits (both subject
+    and body) to stdout, and return the output.
+
+    """
+    fmt_string = ("'%s%n* [#{pr_num}]"
+                  "(https://github.com/elixir-lang/emacs-elixir/pull/{pr_num}) - %b'")
+    return subprocess.check_output([
+        "git",
+        "log",
+        "--pretty=format:%s" % fmt_string,
+        "--merges", "%s..%s" % (start_commit, end_commit)])
+
+
+def release_note_lines(msgs):
+    """Parse the lines from git output and format the strings using the
+    pull request number.
+
+    """
+    ptn = r"Merge pull request #(\d+).*\n([^\n]*)'$"
+    pairs = re.findall(ptn, msgs, re.MULTILINE)
+    return deque(body.format(pr_num=pr_num) for pr_num, body in pairs)
+
+
+def release_header_line(version, release_date=None):
+    release_date = release_date or datetime.date.today().strftime('%Y/%m/%d')
+    return "## %s - %s" % (version, release_date)
+
+
+def prepend(filename, lines, release_header=False):
+    """Write `lines` (i.e. release notes) to file `filename`."""
+    if op.exists(filename):
+        with open(filename, 'r+') as f:
+            first_line = f.read()
+            f.seek(0, 0)
+            f.write('\n\n'.join([lines, first_line]))
+    else:
+        with open(filename, 'w') as f:
+            f.write(lines)
+            f.write('\n')
+
+
+if __name__ == "__main__":
+    import argparse
+    import datetime
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('start_commit', metavar='START_COMMIT_OR_TAG')
+    parser.add_argument('end_commit', metavar='END_COMMIT_OR_TAG')
+    parser.add_argument('--filepath', '-f',
+                        help="Absolute path to output file.")
+    parser.add_argument('--tag', '-t', metavar='NEW_TAG')
+    parser.add_argument(
+        '--date', '-d', metavar='RELEASE_DATE',
+        help="Date of release for listed patch notes. Use yyyy/mm/dd format.")
+    args = parser.parse_args()
+    start, end = args.start_commit, args.end_commit
+    lines = release_note_lines(commit_msgs(start, end))
+
+    if args.tag:
+        lines.appendleft(release_header_line(args.tag, args.date))
+
+    lines = '\n'.join(lines)
+
+    if args.filepath:
+        filename = op.abspath(args.filepath)
+        prepend(filename, lines)
+    else:
+        print lines