Fix false positive about offset that's ensured with array_key_exists

Author: ondrejmirtes

src/Analyser/MutatingScope.php

@@ -4571,8 +4571,35 @@ 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;
+				$exprString = $this->getNodeKey($expr);
+				if (array_key_exists($exprString, $this->expressionTypes)) {
+					// don't add the same type over and over again to improve performance
+					return $this;
+				}
+
+				$expressionTypes = $this->expressionTypes;
+				$expressionTypes[$exprString] = new ExpressionTypeHolder($expr, $type, TrinaryLogic::createYes());
+				$nativeTypes = $this->nativeExpressionTypes;
+				$nativeTypes[$exprString] = new ExpressionTypeHolder($expr, $nativeType, TrinaryLogic::createYes());
+
+				return $this->scopeFactory->create(
+					$this->context,
+					$this->isDeclareStrictTypes(),
+					$this->getFunction(),
+					$this->getNamespace(),
+					$expressionTypes,
+					$nativeTypes,
+					$this->conditionalExpressions,
+					$this->inClosureBindScopeClasses,
+					$this->anonymousFunctionReflection,
+					$this->inFirstLevelStatement,
+					$this->currentlyAssignedExpressions,
+					$this->currentlyAllowedUndefinedExpressions,
+					$this->inFunctionCallsStack,
+					$this->afterExtractCall,
+					$this->parentScope,
+					$this->nativeTypesPromoted,
+				);
 			}
 			return $this->specifyExpressionType($expr, $newType, $newType, TrinaryLogic::createYes());
 		}

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -1000,4 +1000,9 @@ public function testBug10492(): void
 		]);
 	}
 
+	public function testBug13526(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-13526.php'], []);
+	}
+
 }

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

@@ -0,0 +1,26 @@
+<?php
+
+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;
+	}
+}