Avoid refering to "username" in admin templates as USERNAME_FIELD can be updated

[antoliny0919]

Hello!! I made a ticket because I thought that UserAdmin can be improved through USERNAME_FIELD of User model and UserAdmin provided by Django.

This is a way to provide more convenient UserAdmin when django users customize their user models.
The add_fieldsetes in UserAdmin currently provided by Django use the static "username".

@admin.register(User)
class UserAdmin(admin.ModelAdmin):
    add_fieldsets = (
        (
            None,
            {
                "classes": ("wide",),
                "fields": ("username", "usable_password", "password1", "password2"),
            },
        ),
    )

Assuming that the user customizes the user model and uses email as an example of USERNAME_FIELD, UserAdmin must be customized by the user as follows.

# admin.py
class CustomUserAdmin(UserAdmin):
    add_fieldsets = (
        (
            None,
            {
                "classes": ("wide",),
                "fields": ("email", "usable_password", "password1", "password2"),
            },
        ),
    )

# add_form.html
{% block form_top %}
  {% if not is_popup %}
    <p>{% translate 'First, enter a email and password. Then, you’ll be able to edit more user options.' %}</p>
  {% else %}
    <p>{% translate "Enter a email and password." %}</p>
  {% endif %}
{% endblock %}

I think it's better to replace the static "username" with the USERNAME_FIELD dynamic value in this part.

# admin.py
class CustomUserAdmin(UserAdmin):
  add_fieldsets = (
    (
      None,
      {
        "classes": ("wide",),
        "fields": (User.USERNAME_FIELD, "usable_password", "password1", "password2"),
      },
    ),
  )

# add_form.html
{% block form_top %}
  {% if not is_popup %}
    <p>{% blocktranslate %}First, enter a {{ username }} and password. Then, you’ll be able to edit more user options.{% endblocktranslate %}</p>
  {% else %}
    <p>{% blcoktranslate %}Enter a {{ username }} and password.{% endblocktranslate %}</p>
  {% endif %}
{% endblock %}

Even if I keep the original code, there is no problem with the function, but if I replace it with a dynamic value as above, I thought it would be more convenient for the django users to customize the User model, so I suggested this part.

I would also like to know the opinions of Django members and contributors about this improvement.
Thank you for reading my improvements :)

[antoliny0919]

[PR](​https://github.com/django/django/pull/18552)

[Clifford Gama]

Hello @antoliny0919!

Thank you for submitting this ticket and the accompanying PR.

I am accepting the ticket as this seems to be a legitimate accessibility issue when USERNAME_FIELD
has been renamed, and I haven't found another ticket that deals with that specifically.

To be clear: This is about how the prompt text on the user creation form does not respect the USERNAME_FIELD
and always says First, enter a username and password. Then, you’ll be able to edit more user options. with no
way to change that.

[Clifford Gama]

https://code.djangoproject.com/ticket/19368 is related.

[antoliny0919]

Replying to Clifford Gama:

Hello @antoliny0919!

Thank you for submitting this ticket and the accompanying PR.

I am accepting the ticket as this seems to be a legitimate accessibility issue when USERNAME_FIELD
has been renamed, and I haven't found another ticket that deals with that specifically.

To be clear: This is about how the prompt text on the user creation form does not respect the USERNAME_FIELD
and always says First, enter a username and password. Then, you’ll be able to edit more user options. with no
way to change that.

Replying to Clifford Gama:
Thank you so much @Clifford Gama
I checked the advice you gave me in PR.
I also agree with the parts you advised and have revised the source code.

[antoliny0919]

I created PR through good advice!

PR -> ​https://github.com/django/django/pull/18552

[Natalia Bidart]

Hey antoliny, thank you for your work!

Please note that the Triage Stage should not be changed to unreviewed because that means that the ticket (as a report) needs triaging. If, instead, what needs review is your PR, you need to unset the relevant ticket flags (needs improvement, needs tests, needs docs, etc). The contributing docs provides details about this workflow: ​https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#patch-style

[Natalia Bidart]

I've been doing some more investigation for this ticket, and while I agree this should be improved, I think there are a few more places where we need to fix the usage of the literal "username". These are:

• Password reset link on the admin login page, when password reset is enabled. Currently shows "Forgotten your password or username?"
• (Unsure) The password reset email shows "Your username, in case you’ve forgotten:". I guess this should say "your account identifier" or similar?

The PR is on the right path but needs tests for sure.

[antoliny0919]

First of all, I'm sorry for the change in the Triage Stage. I was wondering what the Django members thought about this ticket and I didn't know if I was proceeding correctly.
As you advised, I will look for more parts that need to be fixed with USERNAME_FIELD and commit again.
And I will request it when I need a review.
Thank you for your kind answer.

[antoliny0919]

I have updated all the .po files so that the username template variable can be translated.
Only the part that was previously used as 'username' was changed to %(username)s, but some languages were unable to change the 'username' part because it was difficult to distinguish exactly.
What should I do about these parts?

[Claude Paroz]

.po files should never be touched by non-translators except for cases where tests are affected. Translation updates follow their own workflow (generally during the last weeks before a new major release).

[antoliny0919]

I updated the test code and document!!
I'd appreciate it if you could review my code.

[Sarah Boyce]

Updated the ticket description to reduce the scope overlap with #28608

[Sarah Boyce <42296566+sarahboyce@…>]

In 862026a8:

Fixed #35742 -- Removed hardcoded "username" references in admin templates.

[Claude Paroz <claude@…>]

In 43287cbb:

Refs #35742 -- Used curly quote in add user form message.