Fix doctrine.columnType false positive for single table inheritance

src/Rules/Doctrine/ORM/EntityColumnRule.php

@@ -192,10 +192,21 @@ public function processNode(Node $node, Scope $scope): array
 		}
 
 		$nullable = isset($fieldMapping['nullable']) ? $fieldMapping['nullable'] === true : false;
-		if ($nullable) {
-			$writableToPropertyType = TypeCombinator::addNull($writableToPropertyType);
+
+		// In single table inheritance, the database columns of child entities are always nullable,
+		// because the column is shared with the rest of the hierarchy that does not have the field set
+		// (see Doctrine\ORM\Tools\SchemaTool::gatherColumn). The property itself, however, may stay
+		// non-nullable, so the forced database nullability must not be required on the property side.
+		$nullabilityForcedBySingleTableInheritance = $metadata->isInheritanceTypeSingleTable()
+			&& $metadata->parentClasses !== []
+			&& !isset($fieldMapping['inherited']);
+
+		if ($nullable || $nullabilityForcedBySingleTableInheritance) {
 			$writableToDatabaseType = TypeCombinator::addNull($writableToDatabaseType);
 		}
+		if ($nullable && !$nullabilityForcedBySingleTableInheritance) {
+			$writableToPropertyType = TypeCombinator::addNull($writableToPropertyType);
+		}
 
 		$phpDocType = $node->getPhpDocType();
 		$nativeType = $node->getNativeType() ?? new MixedType();

tests/Rules/Doctrine/ORM/EntityColumnRuleTest.php

@@ -548,6 +548,26 @@ public function testBugSingleEnum(?string $objectManagerLoader): void
 		$this->analyse([__DIR__ . '/data/bug-single-enum.php'], []);
 	}
 
+	/**
+	 * @dataProvider dataObjectManagerLoader
+	 */
+	public function testSingleTableInheritance(?string $objectManagerLoader): void
+	{
+		$this->allowNullablePropertyForRequiredField = false;
+		$this->objectManagerLoader = $objectManagerLoader;
+
+		$this->analyse([__DIR__ . '/data/single-table-inheritance.php'], [
+			[
+				'Property PHPStan\Rules\Doctrine\ORM\SingleTableInheritance\ChildEntity::$childBrokenColumn type mapping mismatch: database can contain string but property expects int.',
+				69,
+			],
+			[
+				'Property PHPStan\Rules\Doctrine\ORM\SingleTableInheritance\ChildEntity::$childBrokenColumn type mapping mismatch: property can contain int but database expects string|null.',
+				69,
+			],
+		]);
+	}
+
 	/**
 	 * @dataProvider dataObjectManagerLoader
 	 */

tests/Rules/Doctrine/ORM/data/single-table-inheritance.php

@@ -0,0 +1,71 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Doctrine\ORM\SingleTableInheritance;
+
+use Doctrine\ORM\Mapping as ORM;
+
+/**
+ * @ORM\Entity()
+ * @ORM\InheritanceType("SINGLE_TABLE")
+ * @ORM\DiscriminatorColumn(name="discr", type="string")
+ * @ORM\DiscriminatorMap({
+ *  "base"="PHPStan\Rules\Doctrine\ORM\SingleTableInheritance\BaseEntity",
+ *  "child"="PHPStan\Rules\Doctrine\ORM\SingleTableInheritance\ChildEntity"
+ * })
+ */
+class BaseEntity
+{
+
+	/**
+	 * @ORM\Id()
+	 * @ORM\GeneratedValue()
+	 * @ORM\Column(type="integer")
+	 *
+	 * @var int
+	 */
+	private $id;
+
+	/**
+	 * @ORM\Column(type="string")
+	 *
+	 * @var string
+	 */
+	private $baseColumn;
+
+}
+
+/**
+ * @ORM\Entity()
+ */
+class ChildEntity extends BaseEntity
+{
+
+	/**
+	 * The column must be nullable in the database because it is shared with the rest of the
+	 * single table inheritance hierarchy, but the property itself is always set.
+	 *
+	 * @ORM\Column(type="string", nullable=true)
+	 *
+	 * @var string
+	 */
+	private $childColumn;
+
+	/**
+	 * Nullable property is fine too.
+	 *
+	 * @ORM\Column(type="string", nullable=true)
+	 *
+	 * @var string|null
+	 */
+	private $childNullableColumn;
+
+	/**
+	 * Genuine type mismatches in child entities are still reported.
+	 *
+	 * @ORM\Column(type="string", nullable=true)
+	 *
+	 * @var int
+	 */
+	private $childBrokenColumn;
+
+}