Revert "Cleanup instanceof Type checks"

src/Analyser/MutatingScope.php

@@ -4367,29 +4367,24 @@ public function specifyExpressionType(Expr $expr, Type $type, Type $nativeType,
 			&& !$expr->dim instanceof Expr\PostInc
 		) {
 			$dimType = $scope->getType($expr->dim)->toArrayKey();
-			if ($dimType->isInteger()->yes() || $dimType->isString()->yes()) {
+			if ($dimType instanceof ConstantIntegerType || $dimType instanceof ConstantStringType) {
 				$exprVarType = $scope->getType($expr->var);
 				if (!$exprVarType instanceof MixedType && !$exprVarType->isArray()->no()) {
 					$types = [
 						new ArrayType(new MixedType(), new MixedType()),
 						new ObjectType(ArrayAccess::class),
 						new NullType(),
 					];
-					if ($dimType->isInteger()->yes()) {
+					if ($dimType instanceof ConstantIntegerType) {
 						$types[] = new StringType();
 					}
-					$offsetValueType = TypeCombinator::intersect($exprVarType, TypeCombinator::union(...$types));
-
-					if ($dimType instanceof ConstantIntegerType || $dimType instanceof ConstantStringType) {
-						$offsetValueType = TypeCombinator::intersect(
-							$offsetValueType,
-							new HasOffsetValueType($dimType, $type),
-						);
-					}
 
 					$scope = $scope->specifyExpressionType(
 						$expr->var,
-						$offsetValueType,
+						TypeCombinator::intersect(
+							TypeCombinator::intersect($exprVarType, TypeCombinator::union(...$types)),
+							new HasOffsetValueType($dimType, $type),
+						),
 						$scope->getNativeType($expr->var),
 						$certainty,
 					);

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -1169,4 +1169,14 @@ public function testBug8719(): void
 		$this->analyse([__DIR__ . '/data/bug-8719.php'], []);
 	}
 
+	public function testBug13694(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = true;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+
+		$this->analyse([__DIR__ . '/data/bug-13694.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Variables/data/bug-13694.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * @param int[] $keys
+ * @param array<int, int|null> $things
+ */
+function evaluateThings(array $keys, array $things): void
+{
+	foreach ($keys as $key) {
+		if (array_key_exists($key, $things) && $things[$key] === null) {
+			echo "Value for key $key is null\n";
+			continue;
+		}
+
+		if (isset($things[$key])) {
+			echo "Key $key is set\n";
+		}
+	}
+}