Fix implemented interface checks for self/static

src/Psalm/Checker/FunctionLikeChecker.php

@@ -772,10 +772,24 @@ abstract class FunctionLikeChecker extends SourceChecker implements StatementsSo
             && $implementer_method_storage->return_type
             && $implementer_classlike_storage->user_defined
         ) {
-            if (!TypeChecker::isContainedBy(
+            $implementer_method_storage_return_type = ExpressionChecker::fleshOutType(
                 $project_checker,
                 $implementer_method_storage->return_type,
+                $implementer_classlike_storage->name,
+                null
+            );
+
+            $guide_method_storage_return_type = ExpressionChecker::fleshOutType(
+                $project_checker,
                 $guide_method_storage->return_type,
+                $guide_classlike_storage->name,
+                null
+            );
+
+            if (!TypeChecker::isContainedBy(
+                $project_checker,
+                $implementer_method_storage_return_type,
+                $guide_method_storage_return_type,
                 false,
                 false,
                 $has_scalar_match,

tests/InterfaceTest.php

@@ -323,6 +323,21 @@ class InterfaceTest extends TestCase
                         }
                     }',
             ],
+            'implementStaticReturn' => [
+                '<?php
+                    class A {}
+                    interface I {
+                      /** @return A */
+                      public function foo();
+                    }
+
+                    class B extends A implements I {
+                      /** @return static */
+                      public function foo() {
+                        return $this;
+                      }
+                    }',
+            ],
         ];
     }