URLField form adds trailing slash to pathless URLs

[coredumperror@…]

On line 678 in forms/fields.py, the URLfield.to_python() method adds a trailing slash to all pathless URLs (e.g. ​http://www.example.com becomes ​http://www.example.com/, but ​http://www.example.com/blah.html is left alone). The comment for why it does this is "the path portion may need to be added before query params", but I have no idea what that has to do with arbitrarily adding a slash to the end of pathless URLs.

Considering that this makes a visible change to the user's desired input, and they have no way to prevent it, I would like to see this changed. Simply removing the offending line (and the if check it's inside) seems to work just fine.

[Daniele Procida]

I think you're right about how it should behave - but since it has behaved in this way for some years, a lot of code may have been written since then that relies on this behaviour, so there could be backward-compatibility issues.

[Robert Rollins]

I don't know the backward-compatibility policies for Django, but a change like this sounds ideal for a major version bump. So could Django 1.7 potentially contain this fix?

[Daniele Procida]

A future version, yes - I don't know about 1.7 though.

​https://docs.djangoproject.com/en/dev/misc/api-stability/

​https://docs.djangoproject.com/en/dev/internals/release-process/#internal-release-deprecation-policy

So, to do away with this, we'd have to:

• provide an alternative function that works correctly
• raise a deprecation warning
• maintain the existing functionality over the full length of the deprecation cycle

but I am not at all sure how this would be achieved here.

[Robert Rollins]

Yeah, that would suck. You'd basically need to define models.URLField2 and forms.URLField2 (or something like that). Though, from my cursory reading of the API Stability page, this seems like a viable "Backwards incompatible change" for a minor version release. It's such a tiny difference.

I wonder if it would be worthwhile, at least, to mention the bug and workaround for it in the docs for URLField. As far as I know, there are currently two ways to work around this:

1) Define a custom field class that derives from CharField, doing the same thing as URLField but using a custom class for it's "form_class" setting in formfield(). That custom class is identical to forms.URLField, except for those offending lines.

2) Define that same forms.URLField-like class, and use it in the "formfield_overrides" setting of your ModelAdmin-derived class in your admin.py file, as seen in my answer here: ​http://stackoverflow.com/a/21944976/464318

[Daniele Procida]

Yes - please do mention the behaviour in the docs, and the longer-term question of what to do about the method's behaviour can be dealt with subsequently.

[ANUBHAV JOSHI]

I think this should not be done...
​http://www.example.com if is appended with trailing '/' will have no effect
But ​http://www.example.com/test will have . What if 'test' is a document and adding a trailing '/' to it will render it as dir

[Claude Paroz]

No, current behavior is not correct. I don't see the point in unconditionally transforming http://www.example.com to http://www.example.com/.

What sort of (serious) compatibility issues could be triggered by changing this?

[ANUBHAV JOSHI]

Replying to claudep:

No, current behavior is not correct. I don't see the point in unconditionally transforming http://www.example.com to http://www.example.com/.

What sort of (serious) compatibility issues could be triggered by changing this?

I meant that '/' is not added in the second case that is correct... I misread the summary and thought it wanted trailing '/'
Also I think the diff is good.

[Robert Rollins]

Yay, a patch! Thank you for taking on this bug, claudep.

I'm curious about the change you made, though: why is it important to add a trailing slash onto a pathless URL that has query args?

[Claude Paroz]

You're right, I probably read #11826 too quickly. I just uploaded a new patch.

[Tim Graham]

For the release note (besides moving it to 1.8): "URLField.to_python no longer adds a trailing slash to pathless URLs." Otherwise, LGTM.

[Claude Paroz <claude@…>]

In d320863878f097b5cbf33ace12e3adb5e02f27e0:

Fixed #22114 -- Stopped adding trailing slashes in URLField.to_python

Thanks coredumperror at gmail.com for the report and Tim Graham
for the review.