Fix phpstan/phpstan#13526: False positive with array_key_exists and union types

Author: staabm

src/Analyser/MutatingScope.php

@@ -3680,10 +3680,6 @@ public function addTypeToExpression(Expr $expr, Type $type): self
 
 		if ($originalExprType->equals($nativeType)) {
 			$newType = TypeCombinator::intersect($type, $originalExprType);
-			if ($newType->isConstantScalarValue()->yes() && $newType->equals($originalExprType)) {
-				// don't add the same type over and over again to improve performance
-				return $this;
-			}
 			return $this->specifyExpressionType($expr, $newType, $newType, TrinaryLogic::createYes());
 		}
 

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -1155,4 +1155,10 @@ public function testBug11276(): void
 		$this->analyse([__DIR__ . '/data/bug-11276.php'], []);
 	}
 
+	public function testBug13526(): void
+	{
+		$this->reportPossiblyNonexistentConstantArrayOffset = true;
+		$this->analyse([__DIR__ . '/data/bug-13526.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-13526.php

@@ -0,0 +1,26 @@
+<?php declare(strict_types=1);
+
+namespace Bug13526;
+
+class Foo
+{
+	public function foo(string $item, bool $a): ?int
+	{
+		$map1 = [
+			'MAP_1_ITEM_1' => 1,
+			'MAP_1_ITEM_2' => 2,
+		];
+		$map2 = [
+			'MAP_2_ITEM_1' => 1,
+			'MAP_2_ITEM_2' => 2,
+		];
+
+		$map = $a ? $map1 : $map2;
+
+		if (array_key_exists($item, $map)) {
+			return $map[$item];
+		}
+
+		return null;
+	}
+}