Remove legacy error notifications infrastructure in favor of store-based one

The storeErrorNotifications feature flag should be removed and the logic behind it should become the new default, more specifically the only version available.

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Acceptance criteria

Part 1: Replace generic errors legacy infrastructure

1. The principal usage of showErrorNotification should be replaced with a datastore-driven alternative, using the core/site store:
   1. It should receive actions setInternalServerError( error ) and clearInternalServerError() and a selector getInternalServerError(), all of which behave similarly to their *AuthError counterparts in the core/user store.
   2. The usages of showErrorNotification that handle errors after a failed module activation (which is basically almost all usages of that function in total) should use setInternalServerError instead (also see next bullet point for context on how to replace the notifications themselves).
   3. A new InternalServerError component should be implemented in assets/js/components/notifications/ which should display the error notification for getInternalServerError (inspired by logic in the AuthError component), with similar appearance (e.g. title, format etc.) that the notifications from the current usages of showErrorNotification have. That component should then be included in the ErrorNotifications component, on top of the two other components.
2. The showErrorNotification function and its remaining usages should be completely removed.
   1. The now unused GenericError component should also be removed.

Part 2: Remove legacy error notifications infrastructure

1. The storeErrorNotifications feature flag should be removed and what’s currently behind it should become the new way to display error notifications.
2. The legacy ErrorNotification component (sometimes referred to as LegacyErrorNotifications) should no longer be used.
3. The googlesitekit.ErrorNotification filter and all of its usages should be removed, e.g.:
   1. the legacy ErrorNotification
   2. the relevant logic in the legacy handleWPError function and in assets/js/components/legacy-notifications/index.js

Implementation Brief

Numbering here matches numbering on AC. Refer to AC first

Part 1

1 .i. Create a new datastore assets/js/googlesitekit/data/site/errors.js. Copy relevant actions and selectors from assets/js/googlesitekit/datastore/user/authentication.js but change names and constants (and ignore all the code for storing authentication state. This datastore is much larger)

1 .ii. Follow AC. Some existing calls to showErrorNotification have a second argument e.g.

showErrorNotification( GenericError, {
	id: 'activate-module-error',
	title: __( 'Internal Server Error', 'google-site-kit' ),
	description: error.message,
	format: 'small',
	type: 'win-error',
} );

and another call passes in an instantiated Notification component showErrorNotification( InvalidCredentialsWarning );

The id, title, description, learnMoreURL, and learnMoreLabel change

So copying AuthError we’d want these passed in error.data

1. iii. Follow IB. Copy like AuthError but pass in the keys above to the inner `Notification component.

2. i. Follow AC

“The usages of showErrorNotification that handle errors after a failed module activation (which is basically almost all usages of that function in total)” The only other usage of showErrorNotification in assets/js/components/legacy-notifications/data-error.js is to be deleted

Part 2

1. Remove storeErrorNotifications from feature-flags.json

2. Remove any usage of this storeErrorNotifications flag from codebase. Not many uses. In Header.js make the component behind the flag always visible. Tests should still pass where previously this was set.

3. Remove <LegacyErrorNotification/> from Header.js (double-check no more instances)

4. Do as per AC

Test Coverage

• Create a assets/js/googlesitekit/data/site/errors.test.js, copying relevant tests from assets/js/googlesitekit/data/site/authentication.test.js
• Currently assets/js/util/test/showErrorNotification.js contains tests for showErrorNotification. Check that setInternalServerError, clearInternalServerError and getInternalServerError cause corresponding changes in InternalServerError (displayed, not displayed, displays correct message)

Visual Regression Changes

• Changes not expected

QA Brief

• Check the new datastore/site/errors store has been created with the following:
  • action: setInternalServerError
  • action: clearInternalServerError
  • selector: getInternalServerError
• Check that all instances of showErrorNotification have been replaced with dispatches to setInternalServerError
• Check the storeErrorNotifications flag has been removed from feature-flags.json and from everywhere in the codebase
• Check the LegacyErrorNotification component has been removed from Header.js and everywhere else in the codebase
• Check that js tests pass

Changelog entry

• N/A

[felixarntz]

@eugene-manuilov @aaemnnosttv Please do not merge this until develop is open towards the 1.38.0 release, since we want to time this to go out together with #1997, #2077, and #2258.

[danielgent]

@Hazlitte that’s definitely a typo on my behalf 😄 Apologies. Put any more questions in here!