3 files changed, 59 insertions, 5 deletions
diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 01b52d916ae..ae76667707e 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -2116,6 +2116,10 @@ class CGDOMJSClass(CGThing):
         self.descriptor = descriptor
 
     def define(self):
+        parentName = self.descriptor.getParentName()
+        if not parentName:
+            parentName = "::dom::bindings::reflector::Reflector"
+
         args = {
             "domClass": DOMClass(self.descriptor),
             "enumerateHook": "None",
@@ -2161,7 +2165,51 @@ static Class: DOMJSClass = DOMJSClass {
         reserved: [0 as *mut _; 3],
     },
     dom_class: %(domClass)s
-};""" % args
+};
+""" % args
+
+
+class CGAssertInheritance(CGThing):
+    """
+    Generate a type assertion for inheritance
+    """
+    def __init__(self, descriptor):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+
+    def define(self):
+        parent = self.descriptor.interface.parent
+        parentName = ""
+        if parent:
+            parentName = parent.identifier.name
+        else:
+            parentName = "::dom::bindings::reflector::Reflector"
+
+        selfName = self.descriptor.interface.identifier.name
+
+        if selfName == "PaintRenderingContext2D":
+            # PaintRenderingContext2D embeds a CanvasRenderingContext2D
+            # instead of a Reflector as an optimization,
+            # but this is fine since CanvasRenderingContext2D
+            # also has a reflector
+            #
+            # FIXME *RenderingContext2D should use Inline
+            parentName = "::dom::canvasrenderingcontext2d::CanvasRenderingContext2D"
+        args = {
+            "parentName": parentName,
+            "selfName": selfName,
+        }
+
+        return """\
+impl %(selfName)s {
+    fn __assert_parent_type(&self) {
+        use dom::bindings::inheritance::HasParent;
+        // If this type assertion fails, make sure the first field of your
+        // DOM struct is of the correct type -- it must be the parent class.
+        let _: &%(parentName)s = self.as_parent();
+    }
+}
+""" % args
 
 
 def str_to_const_array(s):
@@ -6011,6 +6059,8 @@ class CGDescriptor(CGThing):
                 pass
             else:
                 cgThings.append(CGDOMJSClass(descriptor))
+                if not descriptor.interface.isIteratorInterface():
+                    cgThings.append(CGAssertInheritance(descriptor))
                 pass
 
             if descriptor.isGlobal():
diff --git a/components/script/dom/bindings/inheritance.rs b/components/script/dom/bindings/inheritance.rs
index d97843bf42a..c017a806b6e 100644
--- a/components/script/dom/bindings/inheritance.rs
+++ b/components/script/dom/bindings/inheritance.rs
@@ -41,3 +41,8 @@ pub trait Castable: IDLInterface + DomObject + Sized {
         }
     }
 }
+
+pub trait HasParent {
+    type Parent;
+    fn as_parent(&self) -> &Self::Parent;
+}
diff --git a/components/script/dom/filereadersync.rs b/components/script/dom/filereadersync.rs
index cc9a821a073..10095db4961 100644
--- a/components/script/dom/filereadersync.rs
+++ b/components/script/dom/filereadersync.rs
@@ -5,11 +5,10 @@
 use dom::bindings::codegen::Bindings::BlobBinding::BlobMethods;
 use dom::bindings::codegen::Bindings::FileReaderSyncBinding::{FileReaderSyncBinding, FileReaderSyncMethods};
 use dom::bindings::error::{Error, Fallible};
-use dom::bindings::reflector::reflect_dom_object;
+use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::bindings::str::DOMString;
 use dom::blob::Blob;
-use dom::eventtarget::EventTarget;
 use dom::filereader::FileReaderSharedFunctionality;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
@@ -20,13 +19,13 @@ use std::ptr::NonNull;
 
 #[dom_struct]
 pub struct FileReaderSync {
-    eventtarget: EventTarget,
+    reflector: Reflector,
 }
 
 impl FileReaderSync {
     pub fn new_inherited() -> FileReaderSync {
         FileReaderSync {
-            eventtarget: EventTarget::new_inherited(),
+            reflector: Reflector::new(),
         }
     }