Adds required keyword on_delete to ForeignKey and OneToOneField in Django migrations

migratemigrations2django2.py

#!/usr/bin/python3
"""
This script adds on_delete to Django migrations. It works on multi-line
definitions of ForeignKey/OneToOneField which may be in your codebase if you
have black'ened the migration files.

It's not perfect, but it doesn't create syntax errors and you can run black on
the code again afterwards.

First version:
https://gist.github.com/benjaoming/3e5770ffcf029c1e11d9a7f79f2e7f89

https://stackoverflow.com/questions/41571281/easy-way-to-set-on-delete-across-entire-application
https://stackoverflow.com/questions/11898998/how-can-i-write-a-regex-which-matches-non-greedy
https://stackoverflow.com/questions/15474741/python-regex-optional-capture-group
"""
import re
from pathlib import Path


regex = re.compile(
    r"(ForeignKey|OneToOneField)\((\n?\s*([^\)]|\"[^\"]+\")+)(:?[\,\s\n]*)?\)(\,?\n)",
    re.MULTILINE,
)

index = 0
for filename in Path(".").glob("**/migrations/*.py"):
    print(filename)

    contents = open(filename, "r").read()

    matches = re.finditer(regex, contents)

    for a in matches:

        # on_delete is already part of the expression
        if "on_delete" in a.group(0):
            continue

        max_indents = 0
        for line in a.group(0).split("\n"):
            indents = len(line) - len(line.strip())
            max_indents = max(max_indents, indents)

        # A in-line expression of kwargs
        if len(a.group(0).split("\n")) < 5:
            contents = contents.replace(
                a.group(0),
                "{}({}, on_delete=models.CASCADE\n{}),\n{}".format(
                    a.group(1),
                    a.group(2).rstrip(),
                    " " * (max_indents - 4),
                    a.group(3) or "",
                ),
            )
            continue

        contents = contents.replace(
            a.group(0),
            "{}({}    on_delete=models.CASCADE,\n{}),{}\n".format(
                a.group(1), a.group(2), " " * (max_indents - 4), a.group(3) or ""
            ),
        )

    # This is the match, print it to verify
    # print(a.group(0))
    open(filename, "w").write(contents)