git-w.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

'''
git-w.py

A tool to normalize line endings to reduce diffs.
It may normalize line endings to either '\n' (unix) or '\r\n' (windows)
depending on which one best reduces the diff size.
'''

import subprocess

def command_output(cmd):
    return subprocess.Popen(cmd.split(), stdout=subprocess.PIPE).stdout.read().decode('utf-8')

diff_stat_cmd = 'git diff HEAD --numstat'

def parse_diffs_line(line):
    (added, removed, filename) = line.split(None, 2)
    return filename.strip(), int(added) + int(removed)

def diffs(options = ''):
    for line in command_output(diff_stat_cmd + (' ' if options else '') + options).splitlines():
        yield parse_diffs_line(line)

diffs_w = dict(diffs('-w'))

for (filename, stats) in diffs():
    if stats <= diffs_w.get(filename, 0):
        continue
    def check_success(label):
        new_stats_txt = command_output(diff_stat_cmd + ' ' + filename)
        new_stats = parse_diffs_line(new_stats_txt)[1] if new_stats_txt.strip() else 0
        if new_stats >= stats:
            return False
        print('%s: Changed to %s line endings, reducing diff by %d lines.' % (filename, label, stats-new_stats))
        return True
    content = open(filename, 'rb').read()
    unix_style = content.replace(b'\r', b'')
    open(filename, 'wb').write(unix_style)
    if check_success('unix'):
        continue
    windows_style = unix_style.replace(b'\n', b'\r\n')
    open(filename, 'wb').write(windows_style)
    if check_success('windows'):
        continue
    open(filename, 'wb').write(content)
    print('%s: No simple fix' % filename)