Fix #4010 – don’t create interface intersections unless there’s no overlap

src/Psalm/Internal/Type/AssertionReconciler.php

@@ -390,22 +390,13 @@ class AssertionReconciler extends \Psalm\Type\Reconciler
         }
 
         if ($new_type_part instanceof TNamedObject
-            && ((
+            && ($new_type_has_interface || $old_type_has_interface)
-                $new_type_has_interface
+            && !UnionTypeComparator::canExpressionTypesBeIdentical(
-                    && !UnionTypeComparator::isContainedBy(
-                        $codebase,
-                        $existing_var_type,
-                        $new_type
-                    )
-            )
-                || (
-                    $old_type_has_interface
-                    && !UnionTypeComparator::isContainedBy(
                 $codebase,
                 $new_type,
-                        $existing_var_type
+                $existing_var_type,
+                false
             )
-                ))
         ) {
             $acceptable_atomic_types = [];
 

src/Psalm/Internal/Type/Comparator/AtomicTypeComparator.php

@@ -639,7 +639,8 @@ class AtomicTypeComparator
     public static function canBeIdentical(
         Codebase $codebase,
         Type\Atomic $type1_part,
-        Type\Atomic $type2_part
+        Type\Atomic $type2_part,
+        bool $allow_interface_equality = true
     ) : bool {
         if ((get_class($type1_part) === TList::class
                 && $type2_part instanceof Type\Atomic\TNonEmptyList)
@@ -673,11 +674,11 @@ class AtomicTypeComparator
         $first_comparison_result = new TypeComparisonResult();
         $second_comparison_result = new TypeComparisonResult();
 
-        $either_contains = (AtomicTypeComparator::isContainedBy(
+        return (AtomicTypeComparator::isContainedBy(
             $codebase,
             $type1_part,
             $type2_part,
-            true,
+            $allow_interface_equality,
             false,
             $first_comparison_result
         )
@@ -686,7 +687,7 @@ class AtomicTypeComparator
             $codebase,
             $type2_part,
             $type1_part,
-            true,
+            $allow_interface_equality,
             false,
             $second_comparison_result
         )
@@ -694,11 +695,5 @@ class AtomicTypeComparator
         ) || ($first_comparison_result->type_coerced
             && $second_comparison_result->type_coerced
         );
-
-        if ($either_contains) {
-            return true;
-        }
-
-        return false;
     }
 }

src/Psalm/Internal/Type/Comparator/UnionTypeComparator.php

@@ -352,7 +352,8 @@ class UnionTypeComparator
     public static function canExpressionTypesBeIdentical(
         Codebase $codebase,
         Type\Union $type1,
-        Type\Union $type2
+        Type\Union $type2,
+        bool $allow_interface_equality = true
     ): bool {
         if ($type1->hasMixed() || $type2->hasMixed()) {
             return true;
@@ -367,7 +368,8 @@ class UnionTypeComparator
                 $either_contains = AtomicTypeComparator::canBeIdentical(
                     $codebase,
                     $type1_part,
-                    $type2_part
+                    $type2_part,
+                    $allow_interface_equality
                 );
 
                 if ($either_contains) {

tests/InterfaceTest.php

@@ -941,6 +941,40 @@ class InterfaceTest extends TestCase
                     }',
                 'error_message' => 'MissingParamType'
             ],
+            'reconcileAfterClassInstanceof' => [
+                '<?php
+                    interface Base {}
+
+                    class E implements Base {
+                        public function bar() : void {}
+                    }
+
+                    function foobar(Base $foo) : void {
+                        if ($foo instanceof E) {
+                            $foo->bar();
+                        }
+
+                        $foo->bar();
+                    }',
+                'error_message' => 'UndefinedInterfaceMethod - src' . \DIRECTORY_SEPARATOR . 'somefile.php:13:31',
+            ],
+            'reconcileAfterInterfaceInstanceof' => [
+                '<?php
+                    interface Base {}
+
+                    interface E extends Base {
+                        public function bar() : void;
+                    }
+
+                    function foobar(Base $foo) : void {
+                        if ($foo instanceof E) {
+                            $foo->bar();
+                        }
+
+                        $foo->bar();
+                    }',
+                'error_message' => 'UndefinedInterfaceMethod - src' . \DIRECTORY_SEPARATOR . 'somefile.php:13:31',
+            ],
         ];
     }
 }