Support templated @mixin

src/Psalm/Internal/Analyzer/Statements/Expression/Call/AtomicMethodCallAnalyzer.php

@@ -253,6 +253,53 @@ class AtomicMethodCallAnalyzer extends CallAnalyzer
             $statements_analyzer->getFilePath()
         );
 
+        if (!$naive_method_exists
+            && $class_storage->mixin_param
+            && $lhs_type_part instanceof Type\Atomic\TGenericObject
+            && $class_storage->template_types
+        ) {
+            $param_position = \array_search(
+                $class_storage->mixin_param,
+                \array_keys($class_storage->template_types)
+            );
+
+            if ($param_position !== false
+                && isset($lhs_type_part->type_params[$param_position])
+            ) {
+                if ($lhs_type_part->type_params[$param_position]->isSingle()) {
+                    $lhs_type_part_new = array_values(
+                        $lhs_type_part->type_params[$param_position]->getAtomicTypes()
+                    )[0];
+
+                    if ($lhs_type_part_new instanceof Type\Atomic\TNamedObject) {
+                        $new_method_id = new MethodIdentifier(
+                            $lhs_type_part_new->value,
+                            $method_name_lc
+                        );
+
+                        if ($codebase->methods->methodExists(
+                            $new_method_id,
+                            $context->calling_method_id,
+                            $codebase->collect_locations
+                                ? new CodeLocation($source, $stmt->name)
+                                : null,
+                            !$context->collect_initializations
+                                && !$context->collect_mutations
+                                ? $statements_analyzer
+                                : null,
+                            $statements_analyzer->getFilePath()
+                        )) {
+                            $lhs_type_part = $lhs_type_part_new;
+                            $class_storage = $codebase->classlike_storage_provider->get($lhs_type_part->value);
+
+                            $naive_method_exists = true;
+                            $method_id = $new_method_id;
+                        }
+                    }
+                }
+            }
+        }
+
         if (!$naive_method_exists
             || !MethodAnalyzer::isMethodVisible(
                 $method_id,

src/Psalm/Internal/PhpVisitor/ReflectorVisitor.php

@@ -1261,10 +1261,7 @@ class ReflectorVisitor extends PhpParser\NodeVisitorAbstract implements PhpParse
 
                 if ($docblock_info->mixin) {
                     if (isset($this->class_template_types[$docblock_info->mixin])) {
-                        $storage->docblock_issues[] = new InvalidDocblock(
+                        $storage->mixin_param = $docblock_info->mixin;
-                            'Templates are not currently supported for @mixin',
-                            $name_location ?: $class_location
-                        );
                     } else {
                         $mixin_fqcln = Type::getFQCLNFromString(
                             $docblock_info->mixin,

src/Psalm/Internal/Stubs/CoreGenericClasses.phpstub

@@ -96,6 +96,21 @@ interface Iterator extends Traversable {
     public function rewind();
 }
 
+/**
+ * @template TIterator as IteratorAggregate|RecursiveIterator
+ * @mixin TIterator
+ */
+class RecursiveIteratorIterator {
+    /**
+     * @param TIterator $iterator
+     * @param int $mode
+     * @param int $flags
+     *
+     * @return void
+     */
+    public function __construct($iterator, $mode = 0, $flags = 0) {}
+}
+
 /**
  * @template-covariant TKey
  * @template-covariant TValue

src/Psalm/Storage/ClassLikeStorage.php

@@ -102,6 +102,11 @@ class ClassLikeStorage
      */
     public $mixin_fqcln = null;
 
+    /**
+     * @var null|string
+     */
+    public $mixin_param = null;
+
     /**
      * @var array<string, bool>
      */

tests/MixinAnnotationTest.php

@@ -95,6 +95,20 @@ class MixinAnnotationTest extends TestCase
                      */
                     class A extends AParent {}'
             ],
+            'implicitMixin' => [
+                '<?php
+                    function foo(string $dir) : void {
+                        $iterator = new \RecursiveIteratorIterator(
+                            new \RecursiveDirectoryIterator($dir)
+                        );
+
+                        while ($iterator->valid()) {
+                            if (!$iterator->isDot() && $iterator->isLink()) {}
+
+                            $iterator->next();
+                        }
+                    }'
+            ],
         ];
     }
 }