Introduce trait Castable

This trait is used to hold onto the downcast and upcast functions of all
castable IDL interfaces. A castable IDL interface is one which either derives
from or is derived by other interfaces.

The deriving relation is represented by implementations of marker trait
DerivedFrom<T: Castable> generated in InheritTypes.

/^[ ]*use dom::bindings::codegen::InheritTypes::.*(Base|Cast|Derived)/ {
    /::[a-zA-Z]+(Base|Cast|Derived);/d
    s/([{ ])[a-zA-Z]+(Base|Cast|Derived), /\1/g
    s/([{ ])[a-zA-Z]+(Base|Cast|Derived), /\1/g
    s/, [a-zA-Z]+(Base|Cast|Derived)([},])/\2/g
    s/, [a-zA-Z]+(Base|Cast|Derived)([},])/\2/g
    /\{([a-zA-Z]+(Base|Cast|Derived))?\};$/d
    s/\{([a-zA-Z_]+)\};$/\1;/
}

s/([a-zA-Z]+)Cast::from_ref\(\&?\**([a-zA-Z_]+)(\.r\(\))?\)/\2.upcast::<\1>()/g
s/([a-zA-Z]+)Cast::from_ref\(\&?\**([a-zA-Z_]+)(\.[a-zA-Z_]+\(\))?\)/\2\3.upcast::<\1>()/g
s/\(([a-zA-Z]+)Cast::from_ref\)/\(Castable::upcast::<\1>\)/g

s/([a-zA-Z]+)Cast::from_root/Root::upcast::<\1>/g

s/([a-zA-Z]+)Cast::from_layout_js\(\&([a-zA-Z_.]+)\)/\2.upcast::<\1>()/g

s/([a-zA-Z]+)Cast::to_ref\(\&?\**([a-zA-Z_]+)(\.r\(\))?\)/\2.downcast::<\1>()/g
s/([a-zA-Z]+)Cast::to_ref\(\&?\**([a-zA-Z_]+)(\.[a-zA-Z_]+\(\))?\)/\2\3.downcast::<\1>()/g
s/\(([a-zA-Z]+)Cast::to_ref\)/\(Castable::downcast::<\1>\)/g

s/([a-zA-Z]+)Cast::to_root/Root::downcast::<\1>/g

s/([a-zA-Z]+)Cast::to_layout_js\(&?([a-zA-Z_.]+(\(\))?)\)/\2.downcast::<\1>()/g

s/\.is_document\(\)/.is::<Document>()/g
s/\.is_htmlanchorelement\(\)/.is::<HTMLAnchorElement>()/g
s/\.is_htmlappletelement\(\)/.is::<HTMLAppletElement>()/g
s/\.is_htmlareaelement\(\)/.is::<HTMLAreaElement>()/g
s/\.is_htmlbodyelement\(\)/.is::<HTMLBodyElement>()/g
s/\.is_htmlembedelement\(\)/.is::<HTMLEmbedElement>()/g
s/\.is_htmlfieldsetelement\(\)/.is::<HTMLFieldSetElement>()/g
s/\.is_htmlformelement\(\)/.is::<HTMLFormElement>()/g
s/\.is_htmlframesetelement\(\)/.is::<HTMLFrameSetElement>()/g
s/\.is_htmlhtmlelement\(\)/.is::<HTMLHtmlElement>()/g
s/\.is_htmlimageelement\(\)/.is::<HTMLImageElement>()/g
s/\.is_htmllegendelement\(\)/.is::<HTMLLegendElement>()/g
s/\.is_htmloptgroupelement\(\)/.is::<HTMLOptGroupElement>()/g
s/\.is_htmloptionelement\(\)/.is::<HTMLOptionElement>()/g
s/\.is_htmlscriptelement\(\)/.is::<HTMLScriptElement>()/g
s/\.is_htmltabledatacellelement\(\)/.is::<HTMLTableDataCellElement>()/g
s/\.is_htmltableheadercellelement\(\)/.is::<HTMLTableHeaderCellElement>()/g
s/\.is_htmltablerowelement\(\)/.is::<HTMLTableRowElement>()/g
s/\.is_htmltablesectionelement\(\)/.is::<HTMLTableSectionElement>()/g
s/\.is_htmltitleelement\(\)/.is::<HTMLTitleElement>()/g

1 files changed, 36 insertions, 0 deletions

diff --git a/components/script/dom/bindings/js.rs b/components/script/dom/bindings/js.rs
index 1ef1d93a86d..2b908877137 100644
--- a/components/script/dom/bindings/js.rs
+++ b/components/script/dom/bindings/js.rs
@@ -24,6 +24,7 @@
 //!
 
 use core::nonzero::NonZero;
+use dom::bindings::conversions::{Castable, DerivedFrom};
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::trace::trace_reflector;
 use dom::bindings::utils::{Reflectable, Reflector};
@@ -34,6 +35,7 @@ use layout_interface::TrustedNodeAddress;
 use script_task::STACK_ROOTS;
 use std::cell::UnsafeCell;
 use std::default::Default;
+use std::mem;
 use std::ops::Deref;
 use std::ptr;
 use util::mem::HeapSizeOf;
@@ -119,6 +121,24 @@ pub struct LayoutJS<T> {
     ptr: NonZero<*const T>
 }
 
+impl<T: Castable> LayoutJS<T> {
+    /// Cast a DOM object root upwards to one of the interfaces it derives from.
+    pub fn upcast<U>(&self) -> LayoutJS<U> where U: Castable, T: DerivedFrom<U> {
+        unsafe { mem::transmute_copy(self) }
+    }
+
+    /// Cast a DOM object downwards to one of the interfaces it might implement.
+    pub fn downcast<U>(&self) -> Option<LayoutJS<U>> where U: DerivedFrom<T> {
+        unsafe {
+            if (*self.unsafe_get()).is::<U>() {
+                Some(mem::transmute_copy(self))
+            } else {
+                None
+            }
+        }
+    }
+}
+
 impl<T: Reflectable> LayoutJS<T> {
     /// Get the reflector.
     pub unsafe fn get_jsobject(&self) -> *mut JSObject {
@@ -447,6 +467,22 @@ pub struct Root<T: Reflectable> {
     root_list: *const RootCollection,
 }
 
+impl<T: Castable> Root<T> {
+    /// Cast a DOM object root upwards to one of the interfaces it derives from.
+    pub fn upcast<U>(root: Root<T>) -> Root<U> where U: Castable, T: DerivedFrom<U> {
+        unsafe { mem::transmute(root) }
+    }
+
+    /// Cast a DOM object root downwards to one of the interfaces it might implement.
+    pub fn downcast<U>(root: Root<T>) -> Option<Root<U>> where U: DerivedFrom<T> {
+        if root.is::<U>() {
+            Some(unsafe { mem::transmute(root) })
+        } else {
+            None
+        }
+    }
+}
+
 impl<T: Reflectable> Root<T> {
     /// Create a new stack-bounded root for the provided JS-owned value.
     /// It cannot not outlive its associated `RootCollection`, and it gives