LG-3711: Migrate ad hoc alerts to USWDS alert partial

[aduth]

Related: LG-3711
Previously: #4375

Why: Consolidate to single, consistent alert styling.

I've had this branch sitting locally for some time, initially as an exploration of effort involved in migrating the remainder of ad-hoc alert usage.

A few notable findings:

• alert-thumb doesn't map directly to any equivalent design system variant, but I assume it should be eliminated in favor of usa-alert--success.
• Following the logic, there may be an issue prior to these changes where SP custom alert texts may not be showing correctly in non-English locales. Needs more investigation. Edit: See LG-3711: Migrate ad hoc alerts to USWDS alert partial #4418 (comment).
• Not included here (yet): Simple Form may require more work to customize, since with the current configuration it assumes a particular alert markup which is not aligned to the USWDS alerts
  • Edit: Simple Form now customized. See LG-3711: Migrate ad hoc alerts to USWDS alert partial #4418 (comment) and following comments.

  • identity-idp/config/initializers/simple_form.rb

    Lines 6 to 7 in b72d615

    	config.error_notification_tag = :div
    	config.error_notification_class = 'alert alert-error'

[aduth]

• Following the logic, there may be an issue prior to these changes where SP custom alert texts may not be showing correctly in non-English locales. Needs more investigation.

In further testing, this didn't prove to be a problem after all. The initial worry was the difference in how we consider paths between...

identity-idp/app/decorators/service_provider_session_decorator.rb

Lines 126 to 127 in 97fe583

	sign_in_path =
	I18n.locale == :en ? new_user_session_path : new_user_session_path(locale: I18n.locale)

identity-idp/app/views/shared/_sp_alert.html.erb

Line 4 in 97fe583

<% if current_page?(new_user_session_path) %>

But it appears that by the time the view is rendered, the new_user_session_path takes current locale into consideration, which is not the case in the decorator.

[aduth]

Updates:

• The SimpleForm customization we need seems to be only achievable by monkey-patch (6518e3c, a783a7aef). I landed at this after a thorough exploration of the relevant source revealed no additional options for markup customization, and in referencing relevant third-party CSS framework integration documentation suggesting a similar approach. A primary alternative here is to avoid using error_notification altogether, if I'm correct in assuming there's no magic error notification display logic and that we're only using it in a single form (source).
• Remove _alert.scss (48ba7c554) 🎉. I'd have liked to remove all of the alert icon images, but it appears we use some of them elsewhere. I think those should be updated at some point to use the design system icons, so we have consistency.

[zachmargolis]

LGTM

[aduth]

Fortunately the failing tests related to outdated selectors in ec77b7f2a clued me into a regression I'd accidentally introduced, where previously we relied on the decorator's sp_msg method to interpolate some common variables into the message. Since I adapted custom_alert to return the actual alert message, this wasn't happening anymore. Rather than worrying about keeping them in sync, I removed sp_msg and generate_custom_alert, and just made custom_alert return the formatted text.

Updated in 313f1c4e0.

It also prompted me to figure out why my changes to config/service_providers.yml weren't taking effect (needed make setup) so that I could confirm it actually works locally:

[aduth]

I was having some trouble with tests in the previous implementation having the monkey-patch at lib/simple-form. It appeared that the very presence and require of the file was preventing the base class from being defined at all, where the intention was to extend it. Loosely following the convention of Active Support Core Extensions (lib/core_extensions), it appears to be happier at lib/extensions/simple-form.

I might very well be missing something obvious about load order / auto-loading / monkey-patching. Happy to adjust if I am, or if there might be a better place to put these files than creating a new directory.