id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
35314	Django 5 breaks value of Date field rendering correctly in template	Michael	nobody	"This used to work correctly in Django 4. Django 5 removed USE_L10N setting from settings.py

When rendering an input field that is of type `date`:
{{{
  /home/michael/.venv/project/lib/python3.11/site-packages/django/forms/boundfield.py(108)as_widget()
-> return widget.render(
  /home/michael/.venv/project/lib/python3.11/site-packages/django/forms/widgets.py(279)render()
-> context = self.get_context(name, value, attrs)
  /home/michael/.venv/project/lib/python3.11/site-packages/django/forms/widgets.py(332)get_context()
-> context = super().get_context(name, value, attrs)
  /home/michael/.venv/project/lib/python3.11/site-packages/django/forms/widgets.py(271)get_context()
-> ""value"": self.format_value(value),
  /home/michael/.venv/project/lib/python3.11/site-packages/django/forms/widgets.py(555)format_value()
-> value, self.format or formats.get_format(self.format_key)[0]
}}}

We see that ` formats.get_format(self.format_key)` only passes in 1 argument to:

{{{
# django/utils/formats.py(109)get_format()

def get_format(format_type, lang=None, use_l10n=None):
    """"""
    For a specific format type, return the format for the current
    language (locale). Default to the format in the settings.
    format_type is the name of the format, e.g. 'DATE_FORMAT'.

    If use_l10n is provided and is not None, it forces the value to
    be localized (or not), otherwise it's always localized.
    """"""
    if use_l10n is None:
        use_l10n = True
    if use_l10n and lang is None:
        lang = get_language()
    format_type = str(format_type)  # format_type may be lazy.
    cache_key = (format_type, lang)
    try:
        return _format_cache[cache_key]
    except KeyError:
        pass
}}}

this means use_l10n initial value is `None`, which means it will be set to True via the logic:
{{{
    if use_l10n is None:
        use_l10n = True
}}}

So then it sets a language, in my case `en-gb`, which makes results in a `cache_key` of `('DATE_INPUT_FORMATS', 'en-gb')`

Which means the `get_format` method returns `['%d/%m/%Y', '%d/%m/%y', '%Y-%m-%d']`
Which is really bad when `format_type = 'DATE_INPUT_FORMATS'`, because HTML inputs must always be in the format `YYYY/MM/DD`, and hence selecting the first format of `%d/%m/%Y` results in an error in your HTML template when your input is rendered like `<input type=""date"" value=""31/12/2024"">` instead of  `<input type=""date"" value=""2024/12/31"">`


Not that it changes anything, but here is my `DATE_INPUT_FORMATS` from settings.py (it has no `USE_L10N` setting as unfortunately that has been removed):
{{{
DATE_INPUT_FORMATS = [
    '%Y-%m-%d',
]
}}}
"	Bug	closed	Forms	5.0	Normal	duplicate	form date		Unreviewed	0	0	0	0	0	0