Fix #6120: Nullsafe result !== null narrows the caller to non-null

- When assigning from a nullsafe expression (e.g. $result = $clazz?->foo),
  checking $result !== null now correctly narrows $clazz to non-null
- Added non-null/null conditional expressions in processAssignVar alongside
  the existing truthy/falsey ones, so !== null checks trigger narrowing
- Updated bug-13546 test: array_key_first assignment narrowing now correctly
  narrows to non-empty-list/array{} when checking result !== null
- Removed baseline entry for ClassReflection::getCacheKey() which is now
  correctly resolved by the improved narrowing

Author: staabm

phpstan-baseline.neon

@@ -411,12 +411,6 @@ parameters:
 			count: 1
 			path: src/Reflection/ClassReflection.php
 
-		-
-			rawMessage: 'Method PHPStan\Reflection\ClassReflection::getCacheKey() should return string but returns string|null.'
-			identifier: return.type
-			count: 1
-			path: src/Reflection/ClassReflection.php
-
 		-
 			rawMessage: Binary operation "&" between bool|float|int|string|null and bool|float|int|string|null results in an error.
 			identifier: binaryOp.invalid

src/Analyser/NodeScopeResolver.php

@@ -6108,6 +6108,23 @@ private function processAssignVar(
 					$conditionalExpressions = $this->processSureNotTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $falseySpecifiedTypes, $falseyType);
 				}
 
+				$nonNullType = TypeCombinator::removeNull($type);
+				if (
+					!$nonNullType->equals($type)
+					&& !$nonNullType->equals($truthyType)
+				) {
+					$notNullConditionExpr = new Expr\BinaryOp\NotIdentical($assignedExpr, new ConstFetch(new Name('null')));
+					$notNullSpecifiedTypes = $this->typeSpecifier->specifyTypesInCondition($scope, $notNullConditionExpr, TypeSpecifierContext::createTrue());
+					$conditionalExpressions = $this->processSureTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $notNullSpecifiedTypes, $nonNullType);
+					$conditionalExpressions = $this->processSureNotTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $notNullSpecifiedTypes, $nonNullType);
+
+					$nullType = new NullType();
+					$nullConditionExpr = new Expr\BinaryOp\Identical($assignedExpr, new ConstFetch(new Name('null')));
+					$nullSpecifiedTypes = $this->typeSpecifier->specifyTypesInCondition($scope, $nullConditionExpr, TypeSpecifierContext::createTrue());
+					$conditionalExpressions = $this->processSureTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $nullSpecifiedTypes, $nullType);
+					$conditionalExpressions = $this->processSureNotTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $nullSpecifiedTypes, $nullType);
+				}
+
 				$this->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedExpr), $scopeBeforeAssignEval, $storage);
 				$scope = $scope->assignVariable($var->name, $type, $scope->getNativeType($assignedExpr), TrinaryLogic::createYes());
 				foreach ($conditionalExpressions as $exprString => $holders) {

tests/PHPStan/Analyser/nsrt/bug-13546.php

@@ -66,10 +66,10 @@ function mixedLast($mixed): void
 function firstInCondition(array $array)
 {
 	if (($key = array_key_first($array)) !== null) {
-		assertType('list<string>', $array); // could be 'non-empty-list<string>'
+		assertType('non-empty-list<string>', $array);
 		return $array[$key];
 	}
-	assertType('list<string>', $array);
+	assertType('array{}', $array);
 	return null;
 }
 

tests/PHPStan/Analyser/nsrt/bug-6120.php

@@ -27,3 +27,58 @@ public function sayHello(): void
 		}
 	}
 }
+
+final class Clazz
+{
+
+	public int $foo = 0;
+
+	public function bar(?Clazz $clazz): void
+	{
+		$result = $clazz?->foo;
+		assertType('int|null', $result);
+		if ($result !== null) {
+			assertType('Bug6120\Clazz', $clazz);
+			assertType('int', $result);
+			$clazz->bar(null);
+		}
+	}
+
+	public function baz(?Clazz $clazz): void
+	{
+		$result = $clazz?->foo;
+		if ($result === null) {
+			assertType('Bug6120\Clazz|null', $clazz);
+			assertType('null', $result);
+		} else {
+			assertType('Bug6120\Clazz', $clazz);
+			assertType('int', $result);
+		}
+	}
+
+	public function withNullableProperty(?Clazz $clazz): void
+	{
+		$result = $clazz?->nullableProperty;
+		if ($result !== null) {
+			assertType('Bug6120\Clazz', $clazz);
+			assertType('string', $result);
+		}
+	}
+
+	public ?string $nullableProperty = null;
+
+	public function withMethodCall(?Clazz $clazz): void
+	{
+		$result = $clazz?->getFoo();
+		if ($result !== null) {
+			assertType('Bug6120\Clazz', $clazz);
+			assertType('int', $result);
+		}
+	}
+
+	public function getFoo(): int
+	{
+		return $this->foo;
+	}
+
+}