More precise ?? type inference

Author: ondrejmirtes

src/Analyser/MutatingScope.php

@@ -1576,7 +1576,8 @@ private function resolveType(string $exprString, Expr $node): Type
 		}
 
 		if ($node instanceof Expr\BinaryOp\Coalesce) {
-			$leftType = $this->getType($node->left);
+			$issetLeftExpr = new Expr\Isset_([$node->left]);
+			$leftType = $this->filterByTruthyValue($issetLeftExpr)->getType($node->left);
 
 			$result = $this->issetCheck($node->left, static function (Type $type): ?bool {
 				$isNull = $type->isNull();
@@ -1591,7 +1592,7 @@ private function resolveType(string $exprString, Expr $node): Type
 				return TypeCombinator::removeNull($leftType);
 			}
 
-			$rightType = $this->filterByFalseyValue(new Expr\Isset_([$node->left]))->getType($node->right);
+			$rightType = $this->filterByFalseyValue($issetLeftExpr)->getType($node->right);
 
 			if ($result === null) {
 				return TypeCombinator::union(

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -174,6 +174,7 @@ public function dataFileAsserts(): iterable
 		}
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-3875.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10327.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-2611.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-3548.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-10131.php');

tests/PHPStan/Analyser/data/bug-10327.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Bug10327;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param object{optionalKey?: int} $object
+ * @param array{optionalKey?: int} $array
+ */
+function test(object $object, array $array): void
+{
+	$valueObject = $object->optionalKey ?? null;
+
+	assertType('int|null', $valueObject);
+}

tests/PHPStan/Analyser/data/bug-4117.php

@@ -30,14 +30,14 @@ public function getIterator(): ArrayIterator
 	public function broken(int $key)
 	{
 		$item = $this->items[$key] ?? null;
-		assertType('T (class Bug4117Types\GenericList, argument)|null', $item);
+		assertType('T of mixed~null (class Bug4117Types\GenericList, argument)|null', $item);
 		if ($item) {
 			assertType("T of mixed~0|0.0|''|'0'|array{}|false|null (class Bug4117Types\GenericList, argument)", $item);
 		} else {
-			assertType("(array{}&T (class Bug4117Types\GenericList, argument))|(0.0&T (class Bug4117Types\GenericList, argument))|(0&T (class Bug4117Types\GenericList, argument))|(''&T (class Bug4117Types\GenericList, argument))|('0'&T (class Bug4117Types\GenericList, argument))|(T (class Bug4117Types\GenericList, argument)&false)|null", $item);
+			assertType("(array{}&T of mixed~null (class Bug4117Types\GenericList, argument))|(0.0&T of mixed~null (class Bug4117Types\GenericList, argument))|(0&T of mixed~null (class Bug4117Types\GenericList, argument))|(''&T of mixed~null (class Bug4117Types\GenericList, argument))|('0'&T of mixed~null (class Bug4117Types\GenericList, argument))|(T of mixed~null (class Bug4117Types\GenericList, argument)&false)|null", $item);
 		}
 
-		assertType('T (class Bug4117Types\GenericList, argument)|null', $item);
+		assertType('T of mixed~null (class Bug4117Types\GenericList, argument)|null', $item);
 
 		return $item;
 	}
@@ -48,7 +48,7 @@ public function broken(int $key)
 	public function works(int $key)
 	{
 		$item = $this->items[$key] ?? null;
-		assertType('T (class Bug4117Types\GenericList, argument)|null', $item);
+		assertType('T of mixed~null (class Bug4117Types\GenericList, argument)|null', $item);
 
 		return $item;
 	}

tests/PHPStan/Analyser/data/isset-coalesce-empty-type-root.php

@@ -13,7 +13,7 @@
 assertType('bool', isset($sometimesDefinedVariable));
 assertType('bool', isset($neverDefinedVariable));
 
-assertType('mixed', $foo ?? false);
+assertType('mixed~null', $foo ?? false);
 
 $bar = 'abc';
 assertType('\'abc\'', $bar ?? false);