Create an interface for \Drupal\Core\Routing\AdminContext

OK, so this largely was an IDE nobrainer, except for
* @var FQN namespaces,
* @inheritdoc
* removing unused import statements

(Any hints how to tweak PHPStorm settings to automate these?)

Patch flying in.

Setting major as this blocks stable contrib release of tim's initial work in #2621536: [admin_theme] Administration theme

Yeah, i often want to do stuff just to find i already did in my repo... Git says that's your code:

/**
 * Decorates the core AdminContext to check custom admin paths.
 *
 * @todo Do not extend the decorated class, implement an interface after
 *   https://www.drupal.org/node/2708599.
 */
class AdminThemeAdminContext extends AdminContext {

Well OK it may not be a hard blocker, just a kittenkiller...

Some nits. According to $ ag AdminContext you did replace all the instances.

1. +++ b/core/lib/Drupal/Core/Routing/AdminContext.php
   @@ -5,9 +5,9 @@
    /**
   - * Provides a helper class to determine whether the route is an admin one.
   + * {@inheritdoc}
     */
   

   Oh, wow.

   Does this work? I don't think we do this but I can't seem to find any documentation about it.

2. +++ b/core/lib/Drupal/Core/Routing/AdminContextInterface.php
   @@ -0,0 +1,24 @@
   +use Symfony\Component\Routing\Route;
   +
   +
   +/**
   

   Should be only one newline

3. +++ b/core/lib/Drupal/Core/Routing/AdminContextInterface.php
   @@ -0,0 +1,24 @@
   + * Provides a helper class to determine whether the route is an admin one.
   

   I don't think this comment is correct, this is the interface, not the class.

4. +++ b/core/lib/Drupal/Core/Routing/AdminContextInterface.php
   @@ -0,0 +1,24 @@
   +  public function isAdminRoute(Route $route = NULL);
   +}
   \ No newline at end of file
   

   Needs a newline at the end of the file and a newline before the closing bracket of the class.

5. +++ b/core/modules/user/src/Theme/AdminNegotiator.php
   @@ -38,7 +38,7 @@ class AdminNegotiator implements ThemeNegotiatorInterface {
   -   * @var \Drupal\Core\Routing\AdminContext
   +   * @var AdminContextInterface
   

   Should be the FQN.

Thanks for the nits! I'll incorporate them.

5. FQN => MEMO to me, weed out how to make phpstorm do this by itself...

1. inheritdoc => in fact it's the rule:
https://www.drupal.org/docs/develop/coding-standards/api-documentation-a...
(other projects have the rule to leave this as it's just visual clutter and don't add info, but drupal decided for it, i guess api.drupal.org uses it)

#9, that documentation page talks about methods, not classes. I was talking about the class documentation there.

Ah yes i see. Here we go. New patch with nits 1-5.

Exception: Warning: apcu_store(): Unable to allocate memory for pool.

Looks like a CI problem.

Nits were resolved. This looks good to go.

Thank you for creating this issue to improve Drupal.

We are working to decide if this task is still relevant to a currently supported version of Drupal. There hasn't been any discussion here for over 8 years which suggests that this has either been implemented or is no longer relevant. Your thoughts on this will allow a decision to be made.

Since we need more information to move forward with this issue, the status is now Postponed (maintainer needs more info). If we don't receive additional information to help with the issue, it may be closed after three months.

Thanks!

It still doesn't have an interface, so if we still want interfaces for all classes, I'm sure we can revive this. However I am not sure what the current policy is about that.

Discussed this a bit in slack with catch, we don't think this would ever need to be decorated or swapped out for another implementation.
https://drupal.slack.com/archives/C08HS1S71H7/p1772090051771109

I think we can close this issue.

At the very least, we can mark this as normal