RegexValidator needs support for flags passed to `re.compile` (migrations do not allow for compiled patterns)

[Daniel Hahler]

When using a RegexValidator with a compiled pattern, makemigration fails:

ValueError: Cannot serialize: <_sre.SRE_Pattern object at 0x24e8ac0>

A sample model:

from django.core.validators import RegexValidator
pattern = re.compile(r'foo', re.IGNORECASE)
validator = RegexValidator(pattern)

class Model(models.Model):
    foo = models.CharField(
        validators = [validator],
        ...
    )

This is somehow expected, and when passing in the pattern uncompiled it works.
But this won't allow to use re.IGNORE_CASE or other flags for re.compile anymore.

RegexValidator should support a new argument flags, which would then be used for non-compiled patterns (passed on to re.compile).
(​https://github.com/django/django/blob/master/django/core/validators.py#L25)

Let me know, if I could provide a pull request / patch for this (as far as I can see) trivial change.

(It seems like with the new migrations, supporting a pre-compiled pattern is not really relevant anymore (but could be kept still))

(I found this related commit: ​https://github.com/django/django/commit/e565e1332ddfbb44fe7e6139375e3c243af7398d)

[Daniel Hahler]

Since you can pass the flag(s) using (?i) etc, this can be easily worked around.

[Sasha Romijn]

So, with the latest comment, are you suggesting you no longer think patching this is useful?

Patching this makes sense to me: it can make code that uses RegexValidator a lot clearer when flags are passed separately, and the change required in Django is trivial.
For clarity: #21275 explains that the serialisation of validators is an intentional feature.

[Dejan Noveski]

Pull request here ​https://github.com/django/django/pull/2427

[Dejan Noveski]

Updated the patch ​https://github.com/django/django/pull/2427

[Daniel Hahler]

FWIW, the patch looks good to me.

Thanks!

[Sasha Romijn]

Left a comment on the patch. Minor issue in the docs.

[Erik Romijn <erik@…>]

In 4d0c5f61427a8e67552ee2d777fffbadc7aff3b2:

Fixed #22255 -- Added support for specifying re flags in RegexValidator

[Sasha Romijn]

This was also backported to 1.7, thanks for the patch :)