avm1: Fix prototype chain for movies loaded into levels

core/src/loader.rs

@@ -1599,6 +1599,22 @@ impl<'gc> MovieLoader<'gc> {
 
                     mc.replace_with_movie(uc, Some(movie.clone()), true, loader_info);
 
+                    // Update the MovieClip's script object prototype to match the new movie's version.
+                    // This is needed because the level clip may have been created by a loader with
+                    // a different SWF version, and its script object was set up with the wrong prototype.
+                    if !movie.is_action_script_3() {
+                        if let Some(object) = mc.object1() {
+                            let new_proto = uc.avm1.prototypes(mc.swf_version()).movie_clip;
+
+                            object.define_value(
+                                uc.gc(),
+                                istr!(uc, "__proto__"),
+                                new_proto.into(),
+                                Attribute::DONT_ENUM | Attribute::DONT_DELETE,
+                            );
+                        }
+                    }
+
                     // Loaded movies are considered to be timeline-instantiated
                     mc.set_instantiated_by_timeline(true);
 

tests/tests/swfs/avm1/loadmovienum_cross_version_prototype/Target.as

@@ -0,0 +1,12 @@
+// Compile with:
+//  mtasc -main -header 200:150:30 -version 8 Target.as -swf target.swf
+
+class Target {
+  static function main(current) {
+    current.runProtoTest = function() {
+      MovieClip.prototype.customProp = "FROM_SWF8";
+      trace("Target (SWF8): _level2.customProp = " + _level2.customProp);
+      trace("Target (SWF8): _level2.__proto__ === MovieClip.prototype: " + (_level2.__proto__ === MovieClip.prototype));
+    };
+  }
+}

tests/tests/swfs/avm1/loadmovienum_cross_version_prototype/Test.as

@@ -0,0 +1,49 @@
+// Compile with:
+//  mtasc -main -header 200:150:30 -version 6 Test.as -swf test.swf
+
+class Test {
+  static var checkCount = 0;
+  static var phase = 0;
+
+  static function main(current) {
+    trace("Test (SWF6): Loading target.swf into _level2");
+    getURL("target.swf", "_level2");
+
+    current.onEnterFrame = function() {
+      Test.checkCount++;
+
+      if (Test.phase == 0) {
+        // Phase 0: Wait for load and test prototype
+        if (_level2 != undefined && _level2._url != undefined && _level2._url.indexOf("target.swf") >= 0) {
+          trace("Test (SWF6): _level2.getSWFVersion() = " + _level2.getSWFVersion());
+
+          MovieClip.prototype.testProp = "FROM_SWF6";
+          trace("Test (SWF6): _level2.testProp = " + _level2.testProp);
+          trace("Test (SWF6): _level2.__proto__ === MovieClip.prototype: " + (_level2.__proto__ === MovieClip.prototype));
+
+          if (_level2.runProtoTest != undefined) {
+            _level2.runProtoTest();
+          }
+
+          // Now test unload behavior
+          trace("Test (SWF6): Unloading _level2");
+          getURL("", "_level2");
+          Test.phase = 1;
+          Test.checkCount = 0;
+        } else if (Test.checkCount > 60) {
+          trace("Test (SWF6): Timeout");
+          delete current.onEnterFrame;
+        }
+      } else if (Test.phase == 1) {
+        // Phase 1: Check state after unload (wait a couple frames)
+        if (Test.checkCount >= 2) {
+          trace("Test (SWF6): After unload - _level2.__proto__ === MovieClip.prototype: " + (_level2.__proto__ === MovieClip.prototype));
+          // The prototype should still be SWF8's, not SWF6's, because the unloaded
+          // stub keeps the loaded movie's version
+          trace("Test (SWF6): After unload - _level2.testProp = " + _level2.testProp);
+          delete current.onEnterFrame;
+        }
+      }
+    };
+  }
+}

tests/tests/swfs/avm1/loadmovienum_cross_version_prototype/output.txt

@@ -0,0 +1,9 @@
+Test (SWF6): Loading target.swf into _level2
+Test (SWF6): _level2.getSWFVersion() = 8
+Test (SWF6): _level2.testProp = 
+Test (SWF6): _level2.__proto__ === MovieClip.prototype: false
+Target (SWF8): _level2.customProp = FROM_SWF8
+Target (SWF8): _level2.__proto__ === MovieClip.prototype: true
+Test (SWF6): Unloading _level2
+Test (SWF6): After unload - _level2.__proto__ === MovieClip.prototype: false
+Test (SWF6): After unload - _level2.testProp = 

tests/tests/swfs/avm1/loadmovienum_cross_version_prototype/test.toml

@@ -0,0 +1 @@
+num_frames = 6