Adding Form.has_error() to easily check if a given error has happened.

[loic84]

Since #17413, it's possible to know, not only if a field has errors, but also what these errors are.

I propose that we add an API to easily check if a given error has happened.

This would enable logic like this in the view:

if form.has_error('email', 'not_verified'):
    context['email_not_verified'] = True

When a given error happens, I often want to display HTML that describes how to resolve the issue, (usually with links to the relevant sections in the docs which in turn require url reversing); stuffing these in the error message is neither clean (HTML belongs to the templates), nor practical. Following a given error, one may also want to perform actions that typically belongs to the views, like using the message framework.

[loic84]

POC ​https://github.com/loic/django/compare/has_error.

In term of API, I'm hesitating about how to best deal with non-field errors, add_error() accepts a value of None for them, but here has_error(None, 'invalid') could be ambiguous ("Is there any error with the 'invalid' code?" vs "Are there non-field errors with the 'invalid' code?").

With the current implementation non-field errors should be targeted with field=NON_FIELD_ERRORS.

[loic84]

PR ​https://github.com/django/django/pull/2466.

[Tim Graham <timograham@…>]

In 7ac8380799eedb374621317b62ccf026d86ea245:

Fixed #22318 -- Added Form.has_error() to easily check if a given error has happened.