Make EmailValidator use HTML5 validation rather than more complicated regular expressions

[Tim Graham]

As discussed on the ​django-developers mailing list, the regular expressions for validating email addresses are complicated for questionable benefit. We should simplify it to use HTML5 type="email" validation (​possible candidate). A deprecation may be needed to give time for projects to add back more complex validation that they might required.

[Sergei Maertens]

We should also assert that non-ascii characters are allowed in the local part of the e-mail address, see #25986 for background on this issue.

[Chris Butler]

Taking ownership on this at PyCon2016 Sprint. Discussed with Markus and have background on consensus direction a solution should take.

[Claude Paroz]

It would have been nice to know the "consensus direction" mentioned in the comment above!

[Claude Paroz]

#27029 was closed as a duplicate.

[Claude Paroz]

This ​PR only marginally simplifies the regex, but all current tests are still passing, in addition of the non-ASCII local part.
I'm not sure it solves all concerns of this report, to be discussed/confirmed.

[Claude Paroz]

My patch was moved to #27029.

[Jeff Willette]

Replying to timgraham:

As discussed on the ​django-developers mailing list, the regular expressions for validating email addresses are complicated for questionable benefit. We should simplify it to use HTML5 type="email" validation (​possible candidate). A deprecation may be needed to give time for projects to add back more complex validation that they might required.

I've found another possible fix here ​https://html.spec.whatwg.org/multipage/forms.html#valid-e-mail-address, but I have tried this regex and it does not match much out of the ASCII range. What does "HTML5" like browsers match that this regex does not?

[Claude Paroz]

I suggest that Unicode validation be discussed separately in #27029.

[Tim Graham]

​PR from Collin Anderson.

[Haris Ibrahim K. V.]

I've added some documentation that I think will help keep the user expectations clear after digging into the conversation / discussion history of this ticket.

​https://github.com/django/django/pull/8081

[MisRob]

#27932 was closed as a duplicate

[Max Nordlund]

I came across this today and realized that the current regexp, in 1.10.5, contains a type. At least I think it does, since the opening bracket of the second range in user_regex is escaped, but it shouldn't be.

Anyway, I threw together a small PR to fix that, and I hope it can be merge to stable until this lands. I also added a bunch of new examples, and at the very least those should get slurped into the PR from Haris. Hope this helps.

See ​https://github.com/django/django/pull/8187

[Haris Ibrahim K. V.]

Not maintaining the PR any more. Please do feel free to fork and submit a new PR.