Fix for performance issue

Closes phpstan/phpstan#14462

Author: ondrejmirtes

src/Type/TypeCombinator.php

@@ -1154,6 +1154,27 @@ private static function reduceArrays(array $constantArrays, bool $preserveTagged
 					continue;
 				}
 
+				// Merge two single-key arrays sharing the same key when their value
+				// types union into a single type (not a UnionType). This is lossless
+				// and prevents exponential union growth when narrowing nested
+				// ArrayDimFetch expressions on a ConstantArrayType parent (see
+				// phpstan/phpstan#14462).
+				if (
+					$preserveTaggedUnions
+					&& $overlappingKeysCount === 1
+					&& count($arraysToProcess[$i]->getKeyTypes()) === 1
+					&& count($arraysToProcess[$j]->getKeyTypes()) === 1
+				) {
+					$iValueType = $arraysToProcess[$i]->getValueTypes()[0];
+					$jValueType = $arraysToProcess[$j]->getValueTypes()[0];
+					$unionValueType = self::union($iValueType, $jValueType);
+					if (!$unionValueType instanceof UnionType) {
+						$arraysToProcess[$j] = $arraysToProcess[$j]->mergeWith($arraysToProcess[$i]);
+						unset($arraysToProcess[$i]);
+						continue 2;
+					}
+				}
+
 				if (
 					$preserveTaggedUnions
 					&& $overlappingKeysCount === count($arraysToProcess[$i]->getKeyTypes())

tests/PHPStan/Analyser/data/bug-8004.php

@@ -73,7 +73,7 @@ public function getErrorsOnInvalidQuestions(array $importQuiz, int $key): array
             }
         }
 
-		assertType("list<array{line: int, type: 'empty_answer'|'empty_question'|'invalid_answer_1_too_long'|'invalid_answer_1_type'|'invalid_answer_2_too_long'|'invalid_answer_2_type'|'invalid_answer_3_too_long'|'invalid_answer_3_type'|'invalid_answer_4_too_long'|'invalid_answer_4_type'|'invalid_question_too_long'|'invalid_right_answer', value: int}&oversized-array>&oversized-array", $errors);
+		assertType("list<array{line: int, type: 'empty_answer'|'empty_question'|'invalid_answer_1_too_long'|'invalid_answer_1_type'|'invalid_answer_2_too_long'|'invalid_answer_2_type'|'invalid_answer_3_too_long'|'invalid_answer_3_type'|'invalid_answer_4_too_long'|'invalid_answer_4_type'|'invalid_question_too_long'|'invalid_right_answer', value: int}>", $errors);
 
         return $errors;
     }

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -106,7 +106,7 @@ public function testRule(): void
 				145,
 			],
 			[
-				'Offset \'c\' might not exist on array{c: false}|array{c: true}|array{e: true}.',
+				'Offset \'c\' might not exist on array{c: bool}|array{e: true}.',
 				171,
 			],
 			[

tests/bench/data/bug-14462.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14462;
+
+/** @return array{menu: array<non-empty-string, bool>} */
+function get_config(): array {
+	return ['menu' => []];
+}
+
+$config = get_config();
+
+$data = [ ];
+if ($config['menu']['notefrais']) {
+	$data[] = [ 'name' => 'notefrais', 'menu' => 'notefrais_base' ];
+}
+if ($config['menu']['achat']) {
+	$data[] = [ 'name' => 'achat', 'menu' => 'achat_base' ];
+}
+
+if ($config['menu']['vente-commande_planning'] || $config['menu']['vente-commande']) {
+	$data[] = [ 'name' => 'vente' , 'menu' => 'vente_order_recent' ];
+}
+if ($config['menu']['vente-commande_planning']) {
+	$data[] = [ 'name' => 'vente', 'menu' => 'vente_base_planned' ];
+}
+if ($config['menu']['vente-commande']) {
+	$data[] = [ 'name' => 'vente', 'menu' => 'vente_base_com' ];
+}
+if ($config['menu']['carte']) {
+	$data[] = [ 'name' => 'carte', 'menu' => '' ];
+}
+if ($config['menu']['crm']) {
+	$data[] = [ 'name' => 'crm', 'menu' => 'crm_suivi' ];
+}
+if ($config['menu']['inventaire']) {
+	$data[] = [ 'name' => 'inventaire', 'menu' => 'inventaire_base' ];
+}
+
+
+foreach ($data as $row) {
+	$stack = [ ];
+	if ($row['menu'] === 'vente_order_recent') {
+		$stack[] = 'f';
+	}
+	else {
+		$stack[] = 'g';
+	}
+}