Fix doctrine#9095 by re-applying doctrine#9096

Since doctrine#10411 has been merged, no more need to specify all intermediate
abstract entity classes.

Thus, we can relax the schema validator check as requested in doctrine#9095. The
reasons given in doctrine#9142 no longer apply.

Fixes doctrine#9095
Closes doctrine#9096

lib/Doctrine/ORM/Tools/SchemaValidator.php

@@ -253,7 +253,7 @@ public function validateClass(ClassMetadataInfo $class)
             }
         }
 
-        if (! $class->isInheritanceTypeNone() && ! $class->isRootEntity() && ! $class->isMappedSuperclass && array_search($class->name, $class->discriminatorMap, true) === false) {
+        if (! $class->isInheritanceTypeNone() && ! $class->isRootEntity() && ($class->reflClass !== null && ! $class->reflClass->isAbstract()) && ! $class->isMappedSuperclass && array_search($class->name, $class->discriminatorMap, true) === false) {
             $ce[] = "Entity class '" . $class->name . "' is part of inheritance hierarchy, but is " .
                 "not mapped in the root entity '" . $class->rootEntityName . "' discriminator map. " .
                 'All subclasses must be listed in the discriminator map.';

tests/Doctrine/Tests/ORM/Tools/SchemaValidatorTest.php

@@ -221,6 +221,14 @@ public function testMappedSuperclassNotPresentInDiscriminator(): void
 
         $this->assertEquals([], $ce);
     }
+
+    public function testAbstractChildClassNotPresentInDiscriminator(): void
+    {
+        $class1 = $this->em->getClassMetadata(Issue9095AbstractChild::class);
+        $ce     = $this->validator->validateClass($class1);
+
+        self::assertEmpty($ce);
+    }
 }
 
 /** @MappedSuperclass */
@@ -643,3 +651,28 @@ class EmbeddableWithAssociation
      */
     private $cart;
 }
+
+/**
+ * @Entity
+ * @InheritanceType("SINGLE_TABLE")
+ * @DiscriminatorMap({"child" = Issue9095Child::class})
+ */
+abstract class Issue9095Parent
+{
+    /**
+     * @var mixed
+     * @Id
+     * @Column
+     */
+    protected $key;
+}
+
+/** @Entity */
+abstract class Issue9095AbstractChild extends Issue9095Parent
+{
+}
+
+/** @Entity */
+class Issue9095Child extends Issue9095AbstractChild
+{
+}