Remove BC layers in entity system

Only removals, no additions - looks good to me.

Yes IMO we should make 10.0.0-alpha1 as much as possible 9.4 + dependency updates, so that contrib can get a deprecation report for as much as possible without having to update anything yet. Then once it's out start committing deprecation removals.

Going to mark as postponed on the alpha1 issue for now.

Thanks @dww and @catch, I got carried away in my sheer enthusiasm to get rid of deprecations.

Will stop working on those until 10.0.0-alpha1 is out.

Returning $this->entityType->getClass() may cause a problem because it can return a NULL but the signature does not allow it. This causes issues like #3259941: getEntityClass() must be of the type string, null returned.

--- copied from closed issue #3246150: Bundle class changes mean the entity class is now determined by the active entity-type definition -----

This change introduces appears to be causing a compatibility issue described at #3259941: getEntityClass() must be of the type string, null returned where the EntityStorageBase::baseEntityClass is not set, and returns a badly typed result:

 public function getEntityClass(?string $bundle = NULL): string {
    // @todo Simplify this in Drupal 10 to return $this->entityType->getClass().
    // @see https://www.drupal.org/project/drupal/issues/3244802
    return $this->baseEntityClass ?? $this->entityType->getClass();
  }

That function returns a NULL when the baseEntityClass is not set and $this->entityType->getClass() returns NULL too (the signature of that function allows an empty return), but the function signature does not allow for NULL results.

Rewriting it like this fixes the problem, but it may well be a symptom of a deeper problem

    return ($this->baseEntityClass ?? $this->entityType->getClass()) ?? "";

Unpostponing

Removed remains from the Entity namespace

remove legacy test

+++ b/core/lib/Drupal/Core/Entity/Query/Sql/Query.php
@@ -137,8 +137,7 @@ protected function prepare() {
     if (is_null($this->accessCheck)) {
-      $this->accessCheck = TRUE;
-      @trigger_error('Relying on entity queries to check access by default is deprecated in drupal:9.2.0 and an error will be thrown from drupal:10.0.0. Call \Drupal\Core\Entity\Query\QueryInterface::accessCheck() with TRUE or FALSE to specify whether access should be checked. See https://www.drupal.org/node/3201242', E_USER_DEPRECATED);
+      throw new QueryException('Entity query must specify whether access should be checked.');

+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityQueryTest.php
@@ -1358,11 +1359,10 @@ public function testToString() {
-   * @group legacy
    */
   public function testAccessCheckSpecified() {
-    $this->expectDeprecation('Relying on entity queries to check access by default is deprecated in drupal:9.2.0 and an error will be thrown from drupal:10.0.0. Call \Drupal\Core\Entity\Query\QueryInterface::accessCheck() with TRUE or FALSE to specify whether access should be checked. See https://www.drupal.org/node/3201242');
+    $this->expectException(QueryException::class);
+    $this->expectExceptionMessage('Entity query must specify whether access should be checked.');
     $this->storage->getQuery()->execute();

probably could use better wording

I shall leave it up to the committer to decide if the query exception message should be improved and if so to what exactly. For me it is good enough.
All code changes look good to me.
For me it is RTBC.

Opened some phpstan-drupal issues for the deprecation removals.

https://github.com/mglaman/phpstan-drupal/issues/336
https://github.com/mglaman/phpstan-drupal/issues/335
https://github.com/mglaman/phpstan-drupal/issues/334

On the exception message:

Entity query must specify whether access should be checked.

Maybe this?
Entity queries must explicitly set whether the query should be access checked or not. See Drupal\Core\Entity\Query\QueryInterface::accessCheck()

Widening the title to match the patch a bit better.

Fixed the exception message

Looks better in the patch :) Ready to go once the bot is green.

Committed d47cd98 and pushed to 10.0.x. Thanks!