Add IDENTITY() type inference support

src/Type/Doctrine/Query/QueryResultTypeWalker.php

@@ -506,6 +506,55 @@ public function walkFunction($function)
 
 				return $this->marshalType($type);
 
+			case $function instanceof AST\Functions\IdentityFunction:
+				$dqlAlias = $function->pathExpression->identificationVariable;
+				$assocField = $function->pathExpression->field;
+				$queryComp = $this->queryComponents[$dqlAlias];
+				$class = $queryComp['metadata'];
+				$assoc = $class->associationMappings[$assocField];
+				$targetClass = $this->em->getClassMetadata($assoc['targetEntity']);
+
+				if ($function->fieldMapping === null) {
+					$identifierFieldNames = $targetClass->getIdentifierFieldNames();
+					if (count($identifierFieldNames) === 0) {
+						throw new ShouldNotHappenException();
+					}
+
+					$targetFieldName = $identifierFieldNames[0];
+				} else {
+					$targetFieldName = $function->fieldMapping;
+				}
+
+				$typeName = $targetClass->getTypeOfField($targetFieldName);
+				if ($typeName === null) {
+					return $this->marshalType(new MixedType());
+				}
+
+				$fieldMapping = $targetClass->fieldMappings[$targetFieldName] ?? null;
+				if ($fieldMapping === null) {
+					return $this->marshalType(new MixedType());
+				}
+
+				$joinColumn = null;
+
+				foreach ($assoc['joinColumns'] as $item) {
+					if ($item['referencedColumnName'] === $fieldMapping['columnName']) {
+						$joinColumn = $item;
+						break;
+					}
+				}
+
+				if ($joinColumn === null) {
+					return $this->marshalType(new MixedType());
+				}
+
+				$nullable = (bool) ($joinColumn['nullable'] ?? true)
+					|| $this->hasAggregateWithoutGroupBy();
+
+				$fieldType = $this->resolveDatabaseInternalType($typeName, $nullable);
+
+				return $this->marshalType($fieldType);
+
 			default:
 				return $this->marshalType(new MixedType());
 		}

tests/Type/Doctrine/Query/QueryResultTypeWalkerTest.php

@@ -1152,6 +1152,29 @@ public function getTestData(): array
 					FROM		QueryResult\Entities\Many m
 				',
 			],
+			'identity function' => [
+				$this->constantArray([
+					[new ConstantIntegerType(1), TypeCombinator::addNull($this->numericStringOrInt())],
+					[new ConstantIntegerType(2), $this->numericStringOrInt()],
+					[new ConstantIntegerType(3), TypeCombinator::addNull($this->numericStringOrInt())],
+					[new ConstantIntegerType(4), TypeCombinator::addNull(new StringType())],
+					[new ConstantIntegerType(5), TypeCombinator::addNull(new StringType())],
+					[new ConstantIntegerType(6), TypeCombinator::addNull($this->numericStringOrInt())],
+					[new ConstantIntegerType(7), TypeCombinator::addNull(new MixedType())],
+					[new ConstantIntegerType(8), TypeCombinator::addNull($this->numericStringOrInt())],
+				]),
+				'
+					SELECT		IDENTITY(m.oneNull),
+								IDENTITY(m.one),
+								IDENTITY(m.oneDefaultNullability),
+								IDENTITY(m.compoundPk),
+								IDENTITY(m.compoundPk, \'id\'),
+								IDENTITY(m.compoundPk, \'version\'),
+								IDENTITY(m.compoundPkAssoc),
+								IDENTITY(m.compoundPkAssoc, \'version\')
+					FROM		QueryResult\Entities\Many m
+				',
+			],
 			'select nullable association' => [
 				$this->constantArray([
 					[new ConstantIntegerType(1), TypeCombinator::addNull($this->numericStringOrInt())],

tests/Type/Doctrine/data/QueryResult/Entities/CompoundPk.php

@@ -0,0 +1,35 @@
+<?php declare(strict_types=1);
+
+namespace QueryResult\Entities;
+
+use Doctrine\Common\Collections\Collection;
+use Doctrine\ORM\Mapping\Column;
+use Doctrine\ORM\Mapping\Embedded as ORMEmbedded;
+use Doctrine\ORM\Mapping\Entity;
+use Doctrine\ORM\Mapping\Id;
+use Doctrine\ORM\Mapping\JoinColumn;
+use Doctrine\ORM\Mapping\ManyToOne;
+use Doctrine\ORM\Mapping\OneToMany;
+use QueryResult\Entities\One;
+
+/**
+ * @Entity
+ */
+class CompoundPk
+{
+	/**
+	 * @Column(type="string")
+	 * @Id
+	 *
+	 * @var string
+	 */
+	public $id;
+
+	/**
+	 * @Column(type="integer")
+	 * @Id
+	 *
+	 * @var int
+	 */
+	public $version;
+}

tests/Type/Doctrine/data/QueryResult/Entities/CompoundPkAssoc.php

@@ -0,0 +1,36 @@
+<?php declare(strict_types=1);
+
+namespace QueryResult\Entities;
+
+use Doctrine\Common\Collections\Collection;
+use Doctrine\ORM\Mapping\Column;
+use Doctrine\ORM\Mapping\Embedded as ORMEmbedded;
+use Doctrine\ORM\Mapping\Entity;
+use Doctrine\ORM\Mapping\Id;
+use Doctrine\ORM\Mapping\JoinColumn;
+use Doctrine\ORM\Mapping\ManyToOne;
+use Doctrine\ORM\Mapping\OneToMany;
+use QueryResult\Entities\One;
+
+/**
+ * @Entity
+ */
+class CompoundPkAssoc
+{
+	/**
+	 * @ManyToOne(targetEntity="QueryResult\Entities\One")
+	 * @JoinColumn(nullable=false)
+	 * @Id
+	 *
+	 * @var One
+	 */
+	public $one;
+
+	/**
+	 * @Column(type="integer")
+	 * @Id
+	 *
+	 * @var int
+	 */
+	public $version;
+}

tests/Type/Doctrine/data/QueryResult/Entities/Many.php

@@ -6,6 +6,7 @@
 use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\Id;
 use Doctrine\ORM\Mapping\JoinColumn;
+use Doctrine\ORM\Mapping\JoinColumns;
 use Doctrine\ORM\Mapping\ManyToOne;
 
 /**
@@ -78,4 +79,26 @@ class Many
 	 * @var One|null
 	 */
 	public $oneDefaultNullability;
+
+	/**
+	 * @ManyToOne(targetEntity="QueryResult\Entities\CompoundPk")
+	 * @JoinColumns({
+	 *  @JoinColumn(name="compoundPk_id", referencedColumnName="id"),
+	 *  @JoinColumn(name="compoundPk_version", referencedColumnName="version")
+	 * })
+	 *
+	 * @var CompoundPk|null
+	 */
+	public $compoundPk;
+
+	/**
+	 * @ManyToOne(targetEntity="QueryResult\Entities\CompoundPkAssoc")
+	 * @JoinColumns({
+	 *  @JoinColumn(name="compoundPk_one", referencedColumnName="one_id"),
+	 *  @JoinColumn(name="compoundPk_version", referencedColumnName="version")
+	 * })
+	 *
+	 * @var CompoundPkAssoc|null
+	 */
+	public $compoundPkAssoc;
 }