From 23f8967fb520285cb5e4722f376dac0566848668 Mon Sep 17 00:00:00 2001
From: Brown <github@muglug.com>
Date: Thu, 6 Feb 2020 19:40:18 -0500
Subject: [PATCH] Fix conditional class-string template replacement

---
 src/Psalm/Type/Union.php                    | 54 ++++++++++-----------
 tests/Template/ClassTemplateExtendsTest.php | 27 +++++++++++
 2 files changed, 54 insertions(+), 27 deletions(-)

diff --git a/src/Psalm/Type/Union.php b/src/Psalm/Type/Union.php
index a502106d6..3f6302f96 100644
--- a/src/Psalm/Type/Union.php
+++ b/src/Psalm/Type/Union.php
@@ -1186,38 +1186,38 @@ class Union
             } elseif ($atomic_type instanceof Type\Atomic\TTemplateParamClass) {
                 $template_type = isset($template_types[$atomic_type->param_name][$atomic_type->defining_class])
                     ? clone $template_types[$atomic_type->param_name][$atomic_type->defining_class][0]
-                    : Type::getMixed();
+                    : null;
 
-                foreach ($template_type->types as $template_type_part) {
-                    if ($template_type_part instanceof Type\Atomic\TMixed
-                        || $template_type_part instanceof Type\Atomic\TObject
-                    ) {
-                        $unknown_class_string = new Type\Atomic\TClassString();
+                $class_template_type = null;
 
-                        $new_types[$unknown_class_string->getKey()] = $unknown_class_string;
-                        $keys_to_unset[] = $key;
-                    } elseif ($template_type_part instanceof Type\Atomic\TNamedObject) {
-                        $literal_class_string = new Type\Atomic\TClassString(
-                            $template_type_part->value,
-                            $template_type_part
-                        );
+                if ($template_type) {
+                    foreach ($template_type->types as $template_type_part) {
+                        if ($template_type_part instanceof Type\Atomic\TMixed
+                            || $template_type_part instanceof Type\Atomic\TObject
+                        ) {
+                            $class_template_type = new Type\Atomic\TClassString();
+                        } elseif ($template_type_part instanceof Type\Atomic\TNamedObject) {
+                            $class_template_type = new Type\Atomic\TClassString(
+                                $template_type_part->value,
+                                $template_type_part
+                            );
+                        } elseif ($template_type_part instanceof Type\Atomic\TTemplateParam) {
+                            $first_atomic_type = array_values($template_type_part->as->types)[0];
 
-                        $new_types[$literal_class_string->getKey()] = $literal_class_string;
-                        $keys_to_unset[] = $key;
-                    } elseif ($template_type_part instanceof Type\Atomic\TTemplateParam) {
-                        $first_atomic_type = array_values($template_type_part->as->types)[0];
-
-                        $mapped_template_class = new Type\Atomic\TTemplateParamClass(
-                            $template_type_part->param_name,
-                            $template_type_part->as->getId(),
-                            $first_atomic_type instanceof TNamedObject ? $first_atomic_type : null,
-                            $template_type_part->defining_class
-                        );
-
-                        $new_types[$mapped_template_class->getKey()] = $mapped_template_class;
-                        $keys_to_unset[] = $key;
+                            $class_template_type = new Type\Atomic\TTemplateParamClass(
+                                $template_type_part->param_name,
+                                $template_type_part->as->getId(),
+                                $first_atomic_type instanceof TNamedObject ? $first_atomic_type : null,
+                                $template_type_part->defining_class
+                            );
+                        }
                     }
                 }
+
+                if ($class_template_type) {
+                    $keys_to_unset[] = $key;
+                    $new_types[$class_template_type->getKey()] = $class_template_type;
+                }
             } elseif ($atomic_type instanceof Type\Atomic\TTemplateIndexedAccess) {
                 $keys_to_unset[] = $key;
 
diff --git a/tests/Template/ClassTemplateExtendsTest.php b/tests/Template/ClassTemplateExtendsTest.php
index f047810c5..b33c34add 100644
--- a/tests/Template/ClassTemplateExtendsTest.php
+++ b/tests/Template/ClassTemplateExtendsTest.php
@@ -2930,6 +2930,33 @@ class ClassTemplateExtendsTest extends TestCase
                         }
                     }',
             ],
+            'templateInheritanceWithParentTemplateTypes' => [
+                '<?php
+                    /**
+                     * @template T1
+                     */
+                    class A {
+                        /**
+                         * @template T2
+                         * @param class-string<T2> $t
+                         * @return ?T2
+                         */
+                        public function get($t) {
+                            return new $t;
+                        }
+                    }
+
+                    class AChild extends A {
+                        /**
+                         * @template T3
+                         * @param class-string<T3> $t
+                         * @return ?T3
+                         */
+                        public function get($t) {
+                            return new $t;
+                        }
+                    }'
+            ],
         ];
     }