diff-commit-lists

#!/usr/bin/env python3
#
# Diff two commit lists
#

import subprocess
import sys

def read_list(filename):
    data = []
    with open(filename) as fh:
        for line in fh:
            commit, subject = line.strip().split(' ', 1)
            data.append({
                'commit': commit,
                'subject': subject,
            })
    return data

def search_list(list1, subject):
    for line in list1:
        if line['subject'] == subject:
            return line['commit']
    return '-'

def add_common_commits(list1, list2):
    data = []
    for line in list1:
        line['match'] = search_list(list2, line['subject'])
        data.append(line)
    return data

left = read_list(sys.argv[1])
right = read_list(sys.argv[2])

left_plus = add_common_commits(left, right)
right_plus = add_common_commits(right, left)

# Write the processed lists to temp files
with open('/tmp/.left', 'w') as fh:
    for line in left_plus:
        fh.write('{commit:12} {match:12} {subject}\n'.format(**line))
with open('/tmp/.right', 'w') as fh:
    for line in right_plus:
        fh.write('{match:12} {commit:12} {subject}\n'.format(**line))

# Run 'diff' on the two temp files
width = 400
p = subprocess.run(['sdiff', '--ignore-case', '--ignore-all-space',
                    '--ignore-blank-lines', '--width={}'.format(2 * width + 3),
                    '--expand-tabs', '--tabsize=1', '--minimal',
                    '/tmp/.left', '/tmp/.right'],
                   capture_output=True, check=False)

# Process the side-by-side diff output
for line in p.stdout.decode().split('\n')[:-1]:
    left = line[0:width].strip()
    right = line[width + 2:].strip()
    result = line[width + 1:width + 2]

    if result in (' ', '>'):
        # Prefer the right-side ordering
        print(right)
    elif result == '<':
        # Drop the line if it's an out-of-order common commit
        right_commit = line.split(' ')[1]
        if right_commit == '-':
            print(left)
    elif result == '|':
        print(left)
        print(right)
    else:
        print('*************************')
        print('Unable to process line:')
        print(line)
        print('*************************')