14 files changed, 2014 insertions, 0 deletions
diff --git a/xpcom/rust/xpcom/Cargo.toml b/xpcom/rust/xpcom/Cargo.toml
new file mode 100644
index 0000000000..9c8a1ec83b
--- /dev/null
+++ b/xpcom/rust/xpcom/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "xpcom"
+version = "0.1.0"
+authors = ["Nika Layzell <nika@thelayzells.com>"]
+edition = "2018"
+license = "MPL-2.0"
+
+[dependencies]
+cstr = "0.2"
+libc = "0.2"
+nsstring = { path = "../nsstring" }
+nserror = { path = "../nserror" }
+threadbound = "0.1"
+xpcom_macros = { path = "xpcom_macros" }
+thin-vec = { version = "0.2.1", features = ["gecko-ffi"] }
+mozbuild = "0.1"
+
+[features]
+thread_sanitizer = []
+gecko_refcount_logging = []
diff --git a/xpcom/rust/xpcom/src/base.rs b/xpcom/rust/xpcom/src/base.rs
new file mode 100644
index 0000000000..556768a179
--- /dev/null
+++ b/xpcom/rust/xpcom/src/base.rs
@@ -0,0 +1,59 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::interfaces::{nsIInterfaceRequestor, nsISupports};
+use crate::{GetterAddrefs, RefCounted, RefPtr};
+
+#[repr(C)]
+#[derive(Copy, Clone, Eq, PartialEq)]
+/// A "unique identifier". This is modeled after OSF DCE UUIDs.
+pub struct nsID(pub u32, pub u16, pub u16, pub [u8; 8]);
+
+/// Interface IDs
+pub type nsIID = nsID;
+/// Class IDs
+pub type nsCID = nsID;
+
+/// A type which implements XpCom must follow the following rules:
+///
+/// * It must be a legal XPCOM interface.
+/// * The result of a QueryInterface or similar call, passing IID, must return a
+///   valid reference to an object of the given type.
+/// * It must be valid to cast a &self reference to a &nsISupports reference.
+pub unsafe trait XpCom: RefCounted {
+    const IID: nsIID;
+
+    /// Perform a QueryInterface call on this object, attempting to dynamically
+    /// cast it to the requested interface type. Returns Some(RefPtr<T>) if the
+    /// cast succeeded, and None otherwise.
+    fn query_interface<T: XpCom>(&self) -> Option<RefPtr<T>> {
+        let mut ga = GetterAddrefs::<T>::new();
+        unsafe {
+            if (*(self as *const Self as *const nsISupports))
+                .QueryInterface(&T::IID, ga.void_ptr())
+                .succeeded()
+            {
+                ga.refptr()
+            } else {
+                None
+            }
+        }
+    }
+
+    /// Perform a `GetInterface` call on this object, returning `None` if the
+    /// object doesn't implement `nsIInterfaceRequestor`, or can't access the
+    /// interface `T`.
+    fn get_interface<T: XpCom>(&self) -> Option<RefPtr<T>> {
+        let ireq = self.query_interface::<nsIInterfaceRequestor>()?;
+
+        let mut ga = GetterAddrefs::<T>::new();
+        unsafe {
+            if ireq.GetInterface(&T::IID, ga.void_ptr()).succeeded() {
+                ga.refptr()
+            } else {
+                None
+            }
+        }
+    }
+}
diff --git a/xpcom/rust/xpcom/src/components.rs b/xpcom/rust/xpcom/src/components.rs
new file mode 100644
index 0000000000..c83e2df705
--- /dev/null
+++ b/xpcom/rust/xpcom/src/components.rs
@@ -0,0 +1,23 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains convenient accessors for static XPCOM components.
+//!
+//! The contents of this file are generated from
+//! `xpcom/components/gen_static_components.py`.
+
+extern "C" {
+    fn Gecko_GetServiceByModuleID(
+        id: ModuleID,
+        iid: &crate::nsIID,
+        result: *mut *mut libc::c_void,
+    ) -> nserror::nsresult;
+    fn Gecko_CreateInstanceByModuleID(
+        id: ModuleID,
+        iid: &crate::nsIID,
+        result: *mut *mut libc::c_void,
+    ) -> nserror::nsresult;
+}
+
+include!(mozbuild::objdir_path!("xpcom/components/components.rs"));
diff --git a/xpcom/rust/xpcom/src/interfaces/idl.rs b/xpcom/rust/xpcom/src/interfaces/idl.rs
new file mode 100644
index 0000000000..c8d62ce716
--- /dev/null
+++ b/xpcom/rust/xpcom/src/interfaces/idl.rs
@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![allow(bad_style)]
+
+use crate::interfaces::*;
+use crate::*;
+
+// NOTE: This file contains a series of `include!()` invocations, defining all
+// idl interfaces directly within this module.
+include!(mozbuild::objdir_path!("dist/xpcrs/rt/all.rs"));
diff --git a/xpcom/rust/xpcom/src/interfaces/mod.rs b/xpcom/rust/xpcom/src/interfaces/mod.rs
new file mode 100644
index 0000000000..5b9de5cef5
--- /dev/null
+++ b/xpcom/rust/xpcom/src/interfaces/mod.rs
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains the xpcom interfaces exposed to rust code.
+//!
+//! The items in this module come in a few flavours:
+//!
+//! 1. `nsI*`: These are the types for XPCOM interfaces. They should always be
+//!    passed behind a reference, pointer, or `RefPtr`. They may be coerced to
+//!    their base interfaces using the `coerce` method.
+//!
+//! 2. `nsI*Coerce`: These traits provide the implementation mechanics for the
+//!    `coerce` method, and can usually be ignored. *These traits are hidden in
+//!    rustdoc*
+//!
+//! 3. `nsI*VTable`: These structs are the vtable definitions for each type.
+//!    They contain the base interface's vtable, followed by pointers for each
+//!    of the vtable's methods. If direct access is needed, a `*const nsI*` can
+//!    be safely transmuted to a `*const nsI*VTable`. *These structs are hidden
+//!    in rustdoc*
+//!
+//! 4. Typedefs used in idl file definitions.
+
+// Interfaces defined in .idl files
+mod idl;
+pub use self::idl::*;
+
+// Other interfaces which are needed to compile
+mod nonidl;
+pub use self::nonidl::*;
diff --git a/xpcom/rust/xpcom/src/interfaces/nonidl.rs b/xpcom/rust/xpcom/src/interfaces/nonidl.rs
new file mode 100644
index 0000000000..b9e3f1abe2
--- /dev/null
+++ b/xpcom/rust/xpcom/src/interfaces/nonidl.rs
@@ -0,0 +1,180 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains definitions of interfaces which are used in idl files
+//! as forward declarations, but are not actually defined in an idl file.
+//!
+//! NOTE: The IIDs in these files must be kept in sync with the IDL definitions
+//! in the corresponding C++ files.
+
+use crate::nsID;
+
+// XXX: This macro should have an option for a custom base interface instead of
+// nsISupports, such that Document can have nsINode as a base, etc. For now,
+// query_interface should be sufficient.
+macro_rules! nonidl {
+    ($name:ident, $iid:expr) => {
+        /// This interface is referenced from idl files, but not defined in
+        /// them. It exports no methods to rust code.
+        #[repr(C)]
+        pub struct $name {
+            _vtable: *const $crate::interfaces::nsISupportsVTable,
+        }
+
+        unsafe impl $crate::XpCom for $name {
+            const IID: $crate::nsIID = $iid;
+        }
+
+        unsafe impl $crate::RefCounted for $name {
+            #[inline]
+            unsafe fn addref(&self) {
+                self.AddRef();
+            }
+            #[inline]
+            unsafe fn release(&self) {
+                self.Release();
+            }
+        }
+
+        impl ::std::ops::Deref for $name {
+            type Target = $crate::interfaces::nsISupports;
+            #[inline]
+            fn deref(&self) -> &$crate::interfaces::nsISupports {
+                unsafe { ::std::mem::transmute(self) }
+            }
+        }
+    };
+}
+
+// Must be kept in sync with Document.h
+nonidl!(
+    Document,
+    nsID(
+        0xce1f7627,
+        0x7109,
+        0x4977,
+        [0xba, 0x77, 0x49, 0x0f, 0xfd, 0xe0, 0x7a, 0xaa]
+    )
+);
+
+// Must be kept in sync with nsINode.h
+nonidl!(
+    nsINode,
+    nsID(
+        0x70ba4547,
+        0x7699,
+        0x44fc,
+        [0xb3, 0x20, 0x52, 0xdb, 0xe3, 0xd1, 0xf9, 0x0a]
+    )
+);
+
+// Must be kept in sync with nsIContent.h
+nonidl!(
+    nsIContent,
+    nsID(
+        0x8e1bab9d,
+        0x8815,
+        0x4d2c,
+        [0xa2, 0x4d, 0x7a, 0xba, 0x52, 0x39, 0xdc, 0x22]
+    )
+);
+
+// Must be kept in sync with nsIConsoleReportCollector.h
+nonidl!(
+    nsIConsoleReportCollector,
+    nsID(
+        0xdd98a481,
+        0xd2c4,
+        0x4203,
+        [0x8d, 0xfa, 0x85, 0xbf, 0xd7, 0xdc, 0xd7, 0x05]
+    )
+);
+
+// Must be kept in sync with nsIGlobalObject.h
+nonidl!(
+    nsIGlobalObject,
+    nsID(
+        0x11afa8be,
+        0xd997,
+        0x4e07,
+        [0xa6, 0xa3, 0x6f, 0x87, 0x2e, 0xc3, 0xee, 0x7f]
+    )
+);
+
+// Must be kept in sync with nsIScriptElement.h
+nonidl!(
+    nsIScriptElement,
+    nsID(
+        0xe60fca9b,
+        0x1b96,
+        0x4e4e,
+        [0xa9, 0xb4, 0xdc, 0x98, 0x4f, 0x88, 0x3f, 0x9c]
+    )
+);
+
+// Must be kept in sync with nsPIDOMWindow.h
+nonidl!(
+    nsPIDOMWindowOuter,
+    nsID(
+        0x769693d4,
+        0xb009,
+        0x4fe2,
+        [0xaf, 0x18, 0x7d, 0xc8, 0xdf, 0x74, 0x96, 0xdf]
+    )
+);
+
+// Must be kept in sync with nsPIDOMWindow.h
+nonidl!(
+    nsPIDOMWindowInner,
+    nsID(
+        0x775dabc9,
+        0x8f43,
+        0x4277,
+        [0x9a, 0xdb, 0xf1, 0x99, 0x0d, 0x77, 0xcf, 0xfb]
+    )
+);
+
+// Must be kept in sync with nsIScriptContext.h
+nonidl!(
+    nsIScriptContext,
+    nsID(
+        0x54cbe9cf,
+        0x7282,
+        0x421a,
+        [0x91, 0x6f, 0xd0, 0x70, 0x73, 0xde, 0xb8, 0xc0]
+    )
+);
+
+// Must be kept in sync with nsIScriptGlobalObject.h
+nonidl!(
+    nsIScriptGlobalObject,
+    nsID(
+        0x876f83bd,
+        0x6314,
+        0x460a,
+        [0xa0, 0x45, 0x1c, 0x8f, 0x46, 0x2f, 0xb8, 0xe1]
+    )
+);
+
+// Must be kept in sync with nsIScrollObserver.h
+nonidl!(
+    nsIScrollObserver,
+    nsID(
+        0xaa5026eb,
+        0x2f88,
+        0x4026,
+        [0xa4, 0x6b, 0xf4, 0x59, 0x6b, 0x4e, 0xdf, 0x00]
+    )
+);
+
+// Must be kept in sync with nsIWidget.h
+nonidl!(
+    nsIWidget,
+    nsID(
+        0x06396bf6,
+        0x2dd8,
+        0x45e5,
+        [0xac, 0x45, 0x75, 0x26, 0x53, 0xb1, 0xc9, 0x80]
+    )
+);
diff --git a/xpcom/rust/xpcom/src/lib.rs b/xpcom/rust/xpcom/src/lib.rs
new file mode 100644
index 0000000000..ac039ebe76
--- /dev/null
+++ b/xpcom/rust/xpcom/src/lib.rs
@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This crate contains the functionality required in order to both implement
+//! and call XPCOM methods from rust code.
+//!
+//! For documentation on how to implement XPCOM methods, see the documentation
+//! for the [`xpcom_macros`](../xpcom_macros/index.html) crate.
+
+#![allow(non_snake_case)]
+#![allow(non_camel_case_types)]
+
+// re-export the xpcom_macros macro
+pub use xpcom_macros::xpcom;
+
+// Helper functions and data structures are exported in the root of the crate.
+mod base;
+pub use base::*;
+
+// Declarative macro to generate XPCOM method stubs.
+mod method;
+pub use method::*;
+
+// dom::Promise resolving.
+mod promise;
+pub use promise::*;
+
+mod refptr;
+pub use refptr::*;
+
+mod statics;
+pub use statics::*;
+
+// XPCOM interface definitions.
+pub mod interfaces;
+
+// XPCOM component getters.
+pub mod components;
+
+// Implementation details of the xpcom_macros crate.
+#[doc(hidden)]
+pub mod reexports;
diff --git a/xpcom/rust/xpcom/src/method.rs b/xpcom/rust/xpcom/src/method.rs
new file mode 100644
index 0000000000..66c0510bd9
--- /dev/null
+++ b/xpcom/rust/xpcom/src/method.rs
@@ -0,0 +1,241 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use nserror::{nsresult, NS_ERROR_NULL_POINTER};
+
+/// The xpcom_method macro generates a Rust XPCOM method stub that converts
+/// raw pointer arguments to references, calls a Rustic implementation
+/// of the method, writes its return value into the XPCOM method's outparameter,
+/// and returns an nsresult.
+///
+/// In other words, given an XPCOM method like:
+///
+/// ```ignore
+/// interface nsIFooBarBaz : nsISupports {
+///   nsIVariant foo(in AUTF8String bar, [optional] in bool baz);
+/// }
+/// ```
+///
+/// And a Rust implementation that uses #[xpcom] to implement it:
+///
+/// ```ignore
+/// #[xpcom(implement(nsIFooBarBaz), atomic)]
+/// struct FooBarBaz {
+///     // …
+/// }
+/// ```
+///
+/// With the appropriate extern crate and use declarations
+///
+/// ```ignore
+/// extern crate xpcom;
+/// use xpcom::xpcom_method;
+/// ```
+///
+/// Invoking the macro with the name of the XPCOM method, the name of its
+/// Rustic implementation, the set of its arguments, and its return value:
+///
+/// ```ignore
+/// impl FooBarBaz {
+///   xpcom_method!(
+///       foo => Foo(bar: *const nsACString, baz: bool) -> *const nsIVariant
+///   );
+/// }
+/// ```
+///
+/// Results in the macro generating an XPCOM stub like the following:
+///
+/// ```ignore
+/// unsafe fn Foo(&self, bar: *const nsACString, baz: bool, retval: *mut *const nsIVariant) -> nsresult {
+///     let bar = match Ensure::ensure(bar) {
+///         Ok(val) => val,
+///         Err(result) => return result,
+///     };
+///     let baz = match Ensure::ensure(baz) {
+///         Ok(val) => val,
+///         Err(result) => return result,
+///     };
+///
+///     match self.foo(bar, baz) {
+///         Ok(val) => {
+///             val.forget(&mut *retval);
+///             NS_OK
+///         }
+///         Err(error) => {
+///             error!("{}", error);
+///             error.into()
+///         }
+///     }
+/// }
+/// ```
+///
+/// Which calls a Rustic implementation (that you implement) like the following:
+///
+/// ```ignore
+/// impl FooBarBaz {
+///     fn foo(&self, bar: &nsACString, baz: bool) -> Result<RefPtr<nsIVariant>, nsresult> {
+///         // …
+///     }
+/// }
+/// ```
+///
+/// Notes:
+///
+/// On error, the Rustic implementation can return an Err(nsresult) or any
+/// other type that implements Into<nsresult>.  So you can define and return
+/// a custom error type, which the XPCOM stub will convert to nsresult.
+///
+/// This macro assumes that all non-null pointer arguments are valid!
+/// It does ensure that they aren't null, using the `ensure_param` macro.
+/// But it doesn't otherwise check their validity. That makes the function
+/// unsafe, so callers must ensure that they only call it with valid pointer
+/// arguments.
+#[macro_export]
+macro_rules! xpcom_method {
+    // This rule is provided to ensure external modules don't need to import
+    // internal implementation details of xpcom_method.
+    // The @ensure_param rule converts raw pointer arguments to references,
+    // returning NS_ERROR_NULL_POINTER if the argument is_null().
+    //
+    // Notes:
+    //
+    // This rule can be called on a non-pointer copy parameter, but there's no
+    // benefit to doing so.  The macro will just set the value of the parameter
+    // to itself. (This macro does this anyway due to limitations in declarative
+    // macros; it isn't currently possible to distinguish between pointer and
+    // copy types when processing a set of parameters.)
+    //
+    // The macro currently supports only in-parameters (*const nsIFoo); It
+    // doesn't (yet?) support out-parameters (*mut nsIFoo).  The xpcom_method
+    // macro itself does, however, support the return value out-parameter.
+    (@ensure_param $name:ident) => {
+        let $name = match $crate::Ensure::ensure($name) {
+            Ok(val) => val,
+            Err(result) => return result,
+        };
+    };
+
+    // `#[allow(non_snake_case)]` is used for each method because `$xpcom_name`
+    // is almost always UpperCamelCase, and Rust gives a warning that it should
+    // be snake_case. It isn't reasonable to rename the XPCOM methods, so
+    // silence the warning.
+
+    // A method whose return value is a *mut *const nsISomething type.
+    // Example: foo => Foo(bar: *const nsACString, baz: bool) -> *const nsIVariant
+    ($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> *const $retval:ty) => {
+        #[allow(non_snake_case)]
+        unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut *const $retval) -> nsresult {
+            $(xpcom_method!(@ensure_param $param_name);)*
+            match self.$rust_name($($param_name, )*) {
+                Ok(val) => {
+                    val.forget(&mut *retval);
+                    NS_OK
+                }
+                Err(error) => {
+                    error.into()
+                }
+            }
+        }
+    };
+
+    // A method whose return value is a *mut nsAString type.
+    // Example: foo => Foo(bar: *const nsACString, baz: bool) -> nsAString
+    ($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> nsAString) => {
+        #[allow(non_snake_case)]
+        unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut nsAString) -> nsresult {
+            $(xpcom_method!(@ensure_param $param_name);)*
+            match self.$rust_name($($param_name, )*) {
+                Ok(val) => {
+                    (*retval).assign(&val);
+                    NS_OK
+                }
+                Err(error) => {
+                    error.into()
+                }
+            }
+        }
+    };
+
+    // A method whose return value is a *mut nsACString type.
+    // Example: foo => Foo(bar: *const nsACString, baz: bool) -> nsACString
+    ($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> nsACString) => {
+        #[allow(non_snake_case)]
+        unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut nsACString) -> nsresult {
+            $(xpcom_method!(@ensure_param $param_name);)*
+            match self.$rust_name($($param_name, )*) {
+                Ok(val) => {
+                    (*retval).assign(&val);
+                    NS_OK
+                }
+                Err(error) => {
+                    error.into()
+                }
+            }
+        }
+    };
+
+    // A method whose return value is a non-nsA[C]String *mut type.
+    // Example: foo => Foo(bar: *const nsACString, baz: bool) -> bool
+    ($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> $retval:ty) => {
+        #[allow(non_snake_case)]
+        unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut $retval) -> nsresult {
+            $(xpcom_method!(@ensure_param $param_name);)*
+            match self.$rust_name($($param_name, )*) {
+                Ok(val) => {
+                    *retval = val;
+                    NS_OK
+                }
+                Err(error) => {
+                    error.into()
+                }
+            }
+        }
+    };
+
+    // A method that doesn't have a return value.
+    // Example: foo => Foo(bar: *const nsACString, baz: bool)
+    ($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*)) => {
+        #[allow(non_snake_case)]
+        unsafe fn $xpcom_name(&self, $($param_name: $param_type,)*) -> nsresult {
+            $(xpcom_method!(@ensure_param $param_name);)*
+            match self.$rust_name($($param_name, )*) {
+                Ok(_) => NS_OK,
+                Err(error) => {
+                    error.into()
+                }
+            }
+        }
+    };
+}
+
+/// A trait that ensures that a raw pointer isn't null and converts it to
+/// a reference.  Because of limitations in declarative macros, this includes an
+/// implementation for types that are Copy, which simply returns the value
+/// itself.
+#[doc(hidden)]
+pub trait Ensure<T> {
+    unsafe fn ensure(value: T) -> Self;
+}
+
+impl<'a, T: 'a> Ensure<*const T> for Result<&'a T, nsresult> {
+    unsafe fn ensure(ptr: *const T) -> Result<&'a T, nsresult> {
+        if ptr.is_null() {
+            Err(NS_ERROR_NULL_POINTER)
+        } else {
+            Ok(&*ptr)
+        }
+    }
+}
+
+impl<'a, T: 'a> Ensure<*const T> for Result<Option<&'a T>, nsresult> {
+    unsafe fn ensure(ptr: *const T) -> Result<Option<&'a T>, nsresult> {
+        Ok(if ptr.is_null() { None } else { Some(&*ptr) })
+    }
+}
+
+impl<T: Copy> Ensure<T> for Result<T, nsresult> {
+    unsafe fn ensure(copyable: T) -> Result<T, nsresult> {
+        Ok(copyable)
+    }
+}
diff --git a/xpcom/rust/xpcom/src/promise.rs b/xpcom/rust/xpcom/src/promise.rs
new file mode 100644
index 0000000000..0fdab9b6aa
--- /dev/null
+++ b/xpcom/rust/xpcom/src/promise.rs
@@ -0,0 +1,62 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use crate::{
+    create_instance,
+    interfaces::{nsIVariant, nsIWritableVariant},
+    RefCounted,
+};
+
+use cstr::*;
+
+mod ffi {
+    use super::*;
+
+    extern "C" {
+        // These are implemented in dom/promise/Promise.cpp
+        pub fn DomPromise_AddRef(promise: *const Promise);
+        pub fn DomPromise_Release(promise: *const Promise);
+        pub fn DomPromise_RejectWithVariant(promise: *const Promise, variant: *const nsIVariant);
+        pub fn DomPromise_ResolveWithVariant(promise: *const Promise, variant: *const nsIVariant);
+    }
+}
+
+#[repr(C)]
+pub struct Promise {
+    private: [u8; 0],
+
+    /// This field is a phantomdata to ensure that the Promise type and any
+    /// struct containing it is not safe to send across threads, as DOM is
+    /// generally not threadsafe.
+    __nosync: ::std::marker::PhantomData<::std::rc::Rc<u8>>,
+}
+
+impl Promise {
+    pub fn reject_with_undefined(&self) {
+        let variant = create_instance::<nsIWritableVariant>(cstr!("@mozilla.org/variant;1"))
+            .expect("Failed to create writable variant");
+        unsafe {
+            variant.SetAsVoid();
+        }
+        self.reject_with_variant(&variant);
+    }
+
+    pub fn reject_with_variant(&self, variant: &nsIVariant) {
+        unsafe { ffi::DomPromise_RejectWithVariant(self, variant) }
+    }
+
+    pub fn resolve_with_variant(&self, variant: &nsIVariant) {
+        unsafe { ffi::DomPromise_ResolveWithVariant(self, variant) }
+    }
+}
+
+unsafe impl RefCounted for Promise {
+    unsafe fn addref(&self) {
+        ffi::DomPromise_AddRef(self)
+    }
+
+    unsafe fn release(&self) {
+        ffi::DomPromise_Release(self)
+    }
+}
diff --git a/xpcom/rust/xpcom/src/reexports.rs b/xpcom/rust/xpcom/src/reexports.rs
new file mode 100644
index 0000000000..d198899497
--- /dev/null
+++ b/xpcom/rust/xpcom/src/reexports.rs
@@ -0,0 +1,52 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The automatically generated code from `xpcom_macros` depends on some types
+//! which are defined in other libraries which `xpcom` depends on, but which may
+//! not be `extern crate`-ed into the crate the macros are expanded into. This
+//! module re-exports those types from `xpcom` so that they can be used from the
+//! macro.
+// re-export libc so it can be used by the procedural macro.
+pub extern crate libc;
+
+pub use nsstring::{nsACString, nsAString, nsCString, nsString};
+
+pub use nserror::{nsresult, NS_ERROR_NO_INTERFACE, NS_OK};
+
+pub use std::ops::Deref;
+
+/// Helper method used by the xpcom codegen, it is not public API or meant for
+/// calling outside of that context.
+///
+/// Takes a reference to the `this` pointer received from XPIDL, and offsets and
+/// casts it to a reference to the concrete rust `struct` type, `U`.
+///
+/// `vtable_index` is the index, and therefore the offset in pointers, of the
+/// vtable for `T` in `U`.
+///
+/// A reference to `this` is taken, instead of taking `*const T` by value, to use
+/// as a lifetime bound, such that the returned `&U` reference has a bounded
+/// lifetime when used to call the implementation method.
+#[inline]
+pub unsafe fn transmute_from_vtable_ptr<'a, T, U>(
+    this: &'a *const T,
+    vtable_index: usize,
+) -> &'a U {
+    &*((*this as *const *const ()).sub(vtable_index) as *const U)
+}
+
+/// On some ABIs, extra information is included before the vtable's function
+/// pointers which are used to implement RTTI. We build Gecko with RTTI
+/// disabled, however these fields may still be present to support
+/// `dynamic_cast<void*>` on our rust VTables in case they are accessed.
+///
+/// Itanium ABI Layout: https://refspecs.linuxbase.org/cxxabi-1.83.html#vtable
+#[repr(C)]
+pub struct VTableExtra<T> {
+    #[cfg(not(windows))]
+    pub offset: isize,
+    #[cfg(not(windows))]
+    pub typeinfo: *const libc::c_void,
+    pub vtable: T,
+}
diff --git a/xpcom/rust/xpcom/src/refptr.rs b/xpcom/rust/xpcom/src/refptr.rs
new file mode 100644
index 0000000000..8549b6d2f0
--- /dev/null
+++ b/xpcom/rust/xpcom/src/refptr.rs
@@ -0,0 +1,388 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::interfaces::nsISupports;
+use libc;
+use nserror::{nsresult, NS_OK};
+use std::cell::Cell;
+use std::convert::TryInto;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::ops::Deref;
+use std::ptr::{self, NonNull};
+use std::sync::atomic::{self, AtomicUsize, Ordering};
+use threadbound::ThreadBound;
+
+// This should match the definition in mfbt/RefCountType.h, modulo the delicate
+// effort at maintaining binary compatibility with Microsoft COM on Windows.
+pub type MozExternalRefCountType = u32;
+
+/// A trait representing a type which can be reference counted invasively.
+/// The object is responsible for freeing its backing memory when its
+/// reference count reaches 0.
+pub unsafe trait RefCounted {
+    /// Increment the reference count.
+    unsafe fn addref(&self);
+    /// Decrement the reference count, potentially freeing backing memory.
+    unsafe fn release(&self);
+}
+
+/// A smart pointer holding a RefCounted object. The object itself manages its
+/// own memory. RefPtr will invoke the addref and release methods at the
+/// appropriate times to facilitate the bookkeeping.
+#[repr(transparent)]
+pub struct RefPtr<T: RefCounted + 'static> {
+    _ptr: NonNull<T>,
+    // Tell dropck that we own an instance of T.
+    _marker: PhantomData<T>,
+}
+
+impl<T: RefCounted + 'static> RefPtr<T> {
+    /// Construct a new RefPtr from a reference to the refcounted object.
+    #[inline]
+    pub fn new(p: &T) -> RefPtr<T> {
+        unsafe {
+            p.addref();
+        }
+        RefPtr {
+            _ptr: p.into(),
+            _marker: PhantomData,
+        }
+    }
+
+    /// Construct a RefPtr from a raw pointer, addrefing it.
+    #[inline]
+    pub unsafe fn from_raw(p: *const T) -> Option<RefPtr<T>> {
+        let ptr = NonNull::new(p as *mut T)?;
+        ptr.as_ref().addref();
+        Some(RefPtr {
+            _ptr: ptr,
+            _marker: PhantomData,
+        })
+    }
+
+    /// Construct a RefPtr from a raw pointer, without addrefing it.
+    #[inline]
+    pub unsafe fn from_raw_dont_addref(p: *const T) -> Option<RefPtr<T>> {
+        Some(RefPtr {
+            _ptr: NonNull::new(p as *mut T)?,
+            _marker: PhantomData,
+        })
+    }
+
+    /// Write this RefPtr's value into an outparameter.
+    #[inline]
+    pub fn forget(self, into: &mut *const T) {
+        *into = Self::forget_into_raw(self);
+    }
+
+    #[inline]
+    pub fn forget_into_raw(this: RefPtr<T>) -> *const T {
+        let into = &*this as *const T;
+        mem::forget(this);
+        into
+    }
+}
+
+impl<T: RefCounted + 'static> Deref for RefPtr<T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { self._ptr.as_ref() }
+    }
+}
+
+impl<T: RefCounted + 'static> Drop for RefPtr<T> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            self._ptr.as_ref().release();
+        }
+    }
+}
+
+impl<T: RefCounted + 'static> Clone for RefPtr<T> {
+    #[inline]
+    fn clone(&self) -> RefPtr<T> {
+        RefPtr::new(self)
+    }
+}
+
+impl<T: RefCounted + 'static + fmt::Debug> fmt::Debug for RefPtr<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "RefPtr<{:?}>", self.deref())
+    }
+}
+
+// Both `Send` and `Sync` bounds are required for `RefPtr<T>` to implement
+// either, as sharing a `RefPtr<T>` also allows transferring ownership, and
+// vice-versa.
+unsafe impl<T: RefCounted + 'static + Send + Sync> Send for RefPtr<T> {}
+unsafe impl<T: RefCounted + 'static + Send + Sync> Sync for RefPtr<T> {}
+
+macro_rules! assert_layout_eq {
+    ($T:ty, $U:ty) => {
+        const _: [(); std::mem::size_of::<$T>()] = [(); std::mem::size_of::<$U>()];
+        const _: [(); std::mem::align_of::<$T>()] = [(); std::mem::align_of::<$U>()];
+    };
+}
+
+// Assert that `RefPtr<nsISupports>` has the correct memory layout.
+assert_layout_eq!(RefPtr<nsISupports>, *const nsISupports);
+// Assert that the null-pointer optimization applies to `RefPtr<nsISupports>`.
+assert_layout_eq!(RefPtr<nsISupports>, Option<RefPtr<nsISupports>>);
+
+/// A wrapper that binds a RefCounted value to its original thread,
+/// preventing retrieval from other threads and panicking if the value
+/// is dropped on a different thread.
+///
+/// These limitations enable values of this type to be Send + Sync, which is
+/// useful when creating a struct that holds a RefPtr<T> type while being
+/// Send + Sync.  Such a struct can hold a ThreadBoundRefPtr<T> type instead.
+pub struct ThreadBoundRefPtr<T: RefCounted + 'static>(ThreadBound<*const T>);
+
+impl<T: RefCounted + 'static> ThreadBoundRefPtr<T> {
+    pub fn new(ptr: RefPtr<T>) -> Self {
+        let raw: *const T = &*ptr;
+        mem::forget(ptr);
+        ThreadBoundRefPtr(ThreadBound::new(raw))
+    }
+
+    pub fn get_ref(&self) -> Option<&T> {
+        self.0.get_ref().map(|raw| unsafe { &**raw })
+    }
+}
+
+impl<T: RefCounted + 'static> Drop for ThreadBoundRefPtr<T> {
+    fn drop(&mut self) {
+        unsafe {
+            RefPtr::from_raw_dont_addref(self.get_ref().expect("drop() called on wrong thread!"));
+        }
+    }
+}
+
+/// A helper struct for constructing `RefPtr<T>` from raw pointer outparameters.
+/// Holds a `*const T` internally which will be released if non null when
+/// destructed, and can be easily transformed into an `Option<RefPtr<T>>`.
+///
+/// It many cases it may be easier to use the `getter_addrefs` method.
+pub struct GetterAddrefs<T: RefCounted + 'static> {
+    _ptr: *const T,
+    _marker: PhantomData<T>,
+}
+
+impl<T: RefCounted + 'static> GetterAddrefs<T> {
+    /// Create a `GetterAddrefs`, initializing it with the null pointer.
+    #[inline]
+    pub fn new() -> GetterAddrefs<T> {
+        GetterAddrefs {
+            _ptr: ptr::null(),
+            _marker: PhantomData,
+        }
+    }
+
+    /// Get a reference to the internal `*const T`. This method is unsafe,
+    /// as the destructor of this class depends on the internal `*const T`
+    /// being either a valid reference to a value of type `T`, or null.
+    #[inline]
+    pub unsafe fn ptr(&mut self) -> &mut *const T {
+        &mut self._ptr
+    }
+
+    /// Get a reference to the internal `*const T` as a `*mut libc::c_void`.
+    /// This is useful to pass to functions like `GetInterface` which take a
+    /// void pointer outparameter.
+    #[inline]
+    pub unsafe fn void_ptr(&mut self) -> *mut *mut libc::c_void {
+        &mut self._ptr as *mut *const T as *mut *mut libc::c_void
+    }
+
+    /// Transform this `GetterAddrefs` into an `Option<RefPtr<T>>`, without
+    /// performing any addrefs or releases.
+    #[inline]
+    pub fn refptr(self) -> Option<RefPtr<T>> {
+        let p = self._ptr;
+        // Don't run the destructor because we don't want to release the stored
+        // pointer.
+        mem::forget(self);
+        unsafe { RefPtr::from_raw_dont_addref(p) }
+    }
+}
+
+impl<T: RefCounted + 'static> Drop for GetterAddrefs<T> {
+    #[inline]
+    fn drop(&mut self) {
+        if !self._ptr.is_null() {
+            unsafe {
+                (*self._ptr).release();
+            }
+        }
+    }
+}
+
+/// Helper method for calling XPCOM methods which return a reference counted
+/// value through an outparameter. Takes a lambda, which is called with a valid
+/// outparameter argument (`*mut *const T`), and returns a `nsresult`. Returns
+/// either a `RefPtr<T>` with the value returned from the outparameter, or a
+/// `nsresult`.
+///
+/// # NOTE:
+///
+/// Can return `Err(NS_OK)` if the call succeeded, but the outparameter was set
+/// to NULL.
+///
+/// # Usage
+///
+/// ```
+/// let x: Result<RefPtr<T>, nsresult> =
+///     getter_addrefs(|p| iosvc.NewURI(uri, ptr::null(), ptr::null(), p));
+/// ```
+#[inline]
+pub fn getter_addrefs<T: RefCounted, F>(f: F) -> Result<RefPtr<T>, nsresult>
+where
+    F: FnOnce(*mut *const T) -> nsresult,
+{
+    let mut ga = GetterAddrefs::<T>::new();
+    let rv = f(unsafe { ga.ptr() });
+    if rv.failed() {
+        return Err(rv);
+    }
+    ga.refptr().ok_or(NS_OK)
+}
+
+/// The type of the reference count type for xpcom structs.
+///
+/// `#[xpcom(nonatomic)]` will use this type for the `__refcnt` field.
+#[derive(Debug)]
+pub struct Refcnt(Cell<usize>);
+impl Refcnt {
+    /// Create a new reference count value. This is unsafe as manipulating
+    /// Refcnt values is an easy footgun.
+    pub unsafe fn new() -> Self {
+        Refcnt(Cell::new(0))
+    }
+
+    /// Increment the reference count. Returns the new reference count. This is
+    /// unsafe as modifying this value can cause a use-after-free.
+    pub unsafe fn inc(&self) -> MozExternalRefCountType {
+        // XXX: Checked add?
+        let new = self.0.get() + 1;
+        self.0.set(new);
+        new.try_into().unwrap()
+    }
+
+    /// Decrement the reference count. Returns the new reference count. This is
+    /// unsafe as modifying this value can cause a use-after-free.
+    pub unsafe fn dec(&self) -> MozExternalRefCountType {
+        // XXX: Checked sub?
+        let new = self.0.get() - 1;
+        self.0.set(new);
+        new.try_into().unwrap()
+    }
+
+    /// Get the current value of the reference count.
+    pub fn get(&self) -> usize {
+        self.0.get()
+    }
+}
+
+/// The type of the atomic reference count used for xpcom structs.
+///
+/// `#[xpcom(atomic)]` will use this type for the `__refcnt` field.
+///
+/// See `nsISupportsImpl.h`'s `ThreadSafeAutoRefCnt` class for reasoning behind
+/// memory ordering decisions.
+#[derive(Debug)]
+pub struct AtomicRefcnt(AtomicUsize);
+impl AtomicRefcnt {
+    /// Create a new reference count value. This is unsafe as manipulating
+    /// Refcnt values is an easy footgun.
+    pub unsafe fn new() -> Self {
+        AtomicRefcnt(AtomicUsize::new(0))
+    }
+
+    /// Increment the reference count. Returns the new reference count. This is
+    /// unsafe as modifying this value can cause a use-after-free.
+    pub unsafe fn inc(&self) -> MozExternalRefCountType {
+        let result = self.0.fetch_add(1, Ordering::Relaxed) + 1;
+        result.try_into().unwrap()
+    }
+
+    /// Decrement the reference count. Returns the new reference count. This is
+    /// unsafe as modifying this value can cause a use-after-free.
+    pub unsafe fn dec(&self) -> MozExternalRefCountType {
+        let result = self.0.fetch_sub(1, Ordering::Release) - 1;
+        if result == 0 {
+            // We're going to destroy the object on this thread, so we need
+            // acquire semantics to synchronize with the memory released by
+            // the last release on other threads, that is, to ensure that
+            // writes prior to that release are now visible on this thread.
+            if cfg!(feature = "thread_sanitizer") {
+                // TSan doesn't understand atomic::fence, so in order to avoid
+                // a false positive for every time a refcounted object is
+                // deleted, we replace the fence with an atomic operation.
+                self.0.load(Ordering::Acquire);
+            } else {
+                atomic::fence(Ordering::Acquire);
+            }
+        }
+        result.try_into().unwrap()
+    }
+
+    /// Get the current value of the reference count.
+    pub fn get(&self) -> usize {
+        self.0.load(Ordering::Acquire)
+    }
+}
+
+#[cfg(feature = "gecko_refcount_logging")]
+pub mod trace_refcnt {
+    extern "C" {
+        pub fn NS_LogCtor(aPtr: *mut libc::c_void, aTypeName: *const libc::c_char, aSize: u32);
+        pub fn NS_LogDtor(aPtr: *mut libc::c_void, aTypeName: *const libc::c_char, aSize: u32);
+        pub fn NS_LogAddRef(
+            aPtr: *mut libc::c_void,
+            aRefcnt: usize,
+            aClass: *const libc::c_char,
+            aClassSize: u32,
+        );
+        pub fn NS_LogRelease(
+            aPtr: *mut libc::c_void,
+            aRefcnt: usize,
+            aClass: *const libc::c_char,
+            aClassSize: u32,
+        );
+    }
+}
+
+// stub inline methods for the refcount logging functions for when the feature
+// is disabled.
+#[cfg(not(feature = "gecko_refcount_logging"))]
+pub mod trace_refcnt {
+    #[inline]
+    #[allow(non_snake_case)]
+    pub unsafe extern "C" fn NS_LogCtor(_: *mut libc::c_void, _: *const libc::c_char, _: u32) {}
+    #[inline]
+    #[allow(non_snake_case)]
+    pub unsafe extern "C" fn NS_LogDtor(_: *mut libc::c_void, _: *const libc::c_char, _: u32) {}
+    #[inline]
+    #[allow(non_snake_case)]
+    pub unsafe extern "C" fn NS_LogAddRef(
+        _: *mut libc::c_void,
+        _: usize,
+        _: *const libc::c_char,
+        _: u32,
+    ) {
+    }
+    #[inline]
+    #[allow(non_snake_case)]
+    pub unsafe extern "C" fn NS_LogRelease(
+        _: *mut libc::c_void,
+        _: usize,
+        _: *const libc::c_char,
+        _: u32,
+    ) {
+    }
+}
diff --git a/xpcom/rust/xpcom/src/statics.rs b/xpcom/rust/xpcom/src/statics.rs
new file mode 100644
index 0000000000..27f66fdb4b
--- /dev/null
+++ b/xpcom/rust/xpcom/src/statics.rs
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::interfaces::{nsIComponentManager, nsIComponentRegistrar, nsIServiceManager};
+use crate::{GetterAddrefs, RefPtr, XpCom};
+use std::ffi::CStr;
+
+/// Get a reference to the global `nsIComponentManager`.
+///
+/// Can return `None` during shutdown.
+#[inline]
+pub fn component_manager() -> Option<RefPtr<nsIComponentManager>> {
+    unsafe { RefPtr::from_raw(Gecko_GetComponentManager()) }
+}
+
+/// Get a reference to the global `nsIServiceManager`.
+///
+/// Can return `None` during shutdown.
+#[inline]
+pub fn service_manager() -> Option<RefPtr<nsIServiceManager>> {
+    unsafe { RefPtr::from_raw(Gecko_GetServiceManager()) }
+}
+
+/// Get a reference to the global `nsIComponentRegistrar`
+///
+/// Can return `None` during shutdown.
+#[inline]
+pub fn component_registrar() -> Option<RefPtr<nsIComponentRegistrar>> {
+    unsafe { RefPtr::from_raw(Gecko_GetComponentRegistrar()) }
+}
+
+/// Helper for calling `nsIComponentManager::CreateInstanceByContractID` on the
+/// global `nsIComponentRegistrar`.
+///
+/// This method is similar to `do_CreateInstance` in C++.
+#[inline]
+pub fn create_instance<T: XpCom>(id: &CStr) -> Option<RefPtr<T>> {
+    unsafe {
+        let mut ga = GetterAddrefs::<T>::new();
+        if component_manager()?
+            .CreateInstanceByContractID(id.as_ptr(), &T::IID, ga.void_ptr())
+            .succeeded()
+        {
+            ga.refptr()
+        } else {
+            None
+        }
+    }
+}
+
+/// Helper for calling `nsIServiceManager::GetServiceByContractID` on the global
+/// `nsIServiceManager`.
+///
+/// This method is similar to `do_GetService` in C++.
+#[inline]
+pub fn get_service<T: XpCom>(id: &CStr) -> Option<RefPtr<T>> {
+    unsafe {
+        let mut ga = GetterAddrefs::<T>::new();
+        if service_manager()?
+            .GetServiceByContractID(id.as_ptr(), &T::IID, ga.void_ptr())
+            .succeeded()
+        {
+            ga.refptr()
+        } else {
+            None
+        }
+    }
+}
+
+extern "C" {
+    fn Gecko_GetComponentManager() -> *const nsIComponentManager;
+    fn Gecko_GetServiceManager() -> *const nsIServiceManager;
+    fn Gecko_GetComponentRegistrar() -> *const nsIComponentRegistrar;
+}
diff --git a/xpcom/rust/xpcom/xpcom_macros/Cargo.toml b/xpcom/rust/xpcom/xpcom_macros/Cargo.toml
new file mode 100644
index 0000000000..78238ae6d1
--- /dev/null
+++ b/xpcom/rust/xpcom/xpcom_macros/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "xpcom_macros"
+version = "0.1.0"
+authors = ["Nika Layzell <nika@thelayzells.com>"]
+edition = "2018"
+license = "MPL-2.0"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "2", features = ["full"] }
+quote = "1"
+proc-macro2 = "1"
+lazy_static = "1.0"
+mozbuild = "0.1"
diff --git a/xpcom/rust/xpcom/xpcom_macros/src/lib.rs b/xpcom/rust/xpcom/xpcom_macros/src/lib.rs
new file mode 100644
index 0000000000..5c40f699aa
--- /dev/null
+++ b/xpcom/rust/xpcom/xpcom_macros/src/lib.rs
@@ -0,0 +1,812 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This crate provides the `#[xpcom]` custom attribute. This custom attribute
+//! is used in order to implement [`xpcom`] interfaces.
+//!
+//! # Usage
+//!
+//! The easiest way to explain this crate is probably with a usage example. I'll
+//! show you the example, and then we'll destructure it and walk through what
+//! each component is doing.
+//!
+//! ```ignore
+//! // Declaring an XPCOM Struct
+//! #[xpcom(implement(nsIRunnable), atomic)]
+//! struct ImplRunnable {
+//!     i: i32,
+//! }
+//!
+//! // Implementing methods on an XPCOM Struct
+//! impl ImplRunnable {
+//!     unsafe fn Run(&self) -> nsresult {
+//!         println!("{}", self.i);
+//!         NS_OK
+//!     }
+//! }
+//! ```
+//!
+//! ## Declaring an XPCOM Struct
+//!
+//! ```ignore
+//! // This derive should be placed on the initialization struct in order to
+//! // trigger the procedural macro.
+//! #[xpcom(
+//!     // The implement argument should be passed the names of the IDL
+//!     // interfaces which you want to implement. These can be separated by
+//!     // commas if you want to implement multiple interfaces.
+//!     //
+//!     // Some methods use types which we cannot bind to in rust. Interfaces
+//!     // like those cannot be implemented, and a compile-time error will occur
+//!     // if they are listed in this attribute.
+//!     implement(nsIRunnable),
+//!
+//!     // The refcount kind can be specified as one of the following values:
+//!     //  * `atomic` == atomic reference count
+//!     //    ~= NS_DECL_THREADSAFE_ISUPPORTS in C++
+//!     //  * `nonatomic` == non atomic reference count
+//!     //    ~= NS_DECL_ISUPPORTS in C++
+//!     atomic,
+//! )]
+//!
+//! // It is a compile time error to put the `#[xpcom]` attribute on
+//! // an enum, union, or tuple struct.
+//! //
+//! // The macro will generate both the named struct, as well as a version with
+//! // its name prefixed with `Init` which can be used to initialize the type.
+//! struct ImplRunnable {
+//!     i: i32,
+//! }
+//! ```
+//!
+//! The above example will generate `ImplRunnable` and `InitImplRunnable`
+//! structs. The `ImplRunnable` struct will implement the [`nsIRunnable`] XPCOM
+//! interface, and cannot be constructed directly.
+//!
+//! The following methods will be automatically implemented on it:
+//!
+//! ```ignore
+//! // Automatic nsISupports implementation
+//! unsafe fn AddRef(&self) -> MozExternalRefCountType;
+//! unsafe fn Release(&self) -> MozExternalRefCountType;
+//! unsafe fn QueryInterface(&self, uuid: &nsIID, result: *mut *mut libc::c_void) -> nsresult;
+//!
+//! // Allocates and initializes a new instance of this type. The values will
+//! // be moved from the `Init` struct which is passed in.
+//! fn allocate(init: InitImplRunnable) -> RefPtr<Self>;
+//!
+//! // Helper for performing the `query_interface` operation to case to a
+//! // specific interface.
+//! fn query_interface<T: XpCom>(&self) -> Option<RefPtr<T>>;
+//!
+//! // Coerce function for cheaply casting to our base interfaces.
+//! fn coerce<T: ImplRunnableCoerce>(&self) -> &T;
+//! ```
+//!
+//! The [`RefCounted`] interface will also be implemented, so that the type can
+//! be used within the [`RefPtr`] type.
+//!
+//! The `coerce` and `query_interface` methods are backed by the generated
+//! `*Coerce` trait. This trait is impl-ed for every interface implemented by
+//! the trait. For example:
+//!
+//! ```ignore
+//! pub trait ImplRunnableCoerce {
+//!     fn coerce_from(x: &ImplRunnable) -> &Self;
+//! }
+//! impl ImplRunnableCoerce for nsIRunnable { .. }
+//! impl ImplRunnableCoerce for nsISupports { .. }
+//! ```
+//!
+//! ## Implementing methods on an XPCOM Struct
+//!
+//! ```ignore
+//! // Methods should be implemented directly on the generated struct. All
+//! // methods other than `AddRef`, `Release`, and `QueryInterface` must be
+//! // implemented manually.
+//! impl ImplRunnable {
+//!     // The method should have the same name as the corresponding C++ method.
+//!     unsafe fn Run(&self) -> nsresult {
+//!         // Fields defined on the template struct will be directly on the
+//!         // generated struct.
+//!         println!("{}", self.i);
+//!         NS_OK
+//!     }
+//! }
+//! ```
+//!
+//! XPCOM methods implemented in Rust have signatures similar to methods
+//! implemented in C++.
+//!
+//! ```ignore
+//! // nsISupports foo(in long long bar, in AString baz);
+//! unsafe fn Foo(&self, bar: i64, baz: *const nsAString,
+//!               _retval: *mut *const nsISupports) -> nsresult;
+//!
+//! // AString qux(in nsISupports ham);
+//! unsafe fn Qux(&self, ham: *const nsISupports,
+//!               _retval: *mut nsAString) -> nsresult;
+//! ```
+//!
+//! This is a little tedious, so the `xpcom_method!` macro provides a convenient
+//! way to generate wrappers around more idiomatic Rust methods.
+//!
+//! [`xpcom`]: ../xpcom/index.html
+//! [`nsIRunnable`]: ../xpcom/struct.nsIRunnable.html
+//! [`RefCounted`]: ../xpcom/struct.RefCounted.html
+//! [`RefPtr`]: ../xpcom/struct.RefPtr.html
+
+use lazy_static::lazy_static;
+use proc_macro2::{Span, TokenStream};
+use quote::{format_ident, quote, ToTokens};
+use std::collections::{HashMap, HashSet};
+use syn::meta::ParseNestedMeta;
+use syn::punctuated::Punctuated;
+use syn::{parse_macro_input, parse_quote, Field, Fields, Ident, ItemStruct, Token, Type};
+
+macro_rules! bail {
+    (@($t:expr), $s:expr) => {
+        return Err(syn::Error::new_spanned(&$t, &$s[..]))
+    };
+    (@($t:expr), $f:expr, $($e:expr),*) => {
+        return Err(syn::Error::new_spanned(&$t, &format!($f, $($e),*)[..]))
+    };
+    ($s:expr) => {
+        return Err(syn::Error::new(Span::call_site(), &$s[..]))
+    };
+    ($f:expr, $($e:expr),*) => {
+        return Err(syn::Error::new(Span::call_site(), &format!($f, $($e),*)[..]))
+    };
+}
+
+/* These are the structs generated by the rust_macros.py script */
+
+/// A single parameter to an XPCOM method.
+#[derive(Debug)]
+struct Param {
+    name: &'static str,
+    ty: &'static str,
+}
+
+/// A single method on an XPCOM interface.
+#[derive(Debug)]
+struct Method {
+    name: &'static str,
+    params: &'static [Param],
+    ret: &'static str,
+}
+
+/// An XPCOM interface. `methods` will be `Err("reason")` if the interface
+/// cannot be implemented in rust code.
+#[derive(Debug)]
+struct Interface {
+    name: &'static str,
+    base: Option<&'static str>,
+    sync: bool,
+    methods: Result<&'static [Method], &'static str>,
+}
+
+impl Interface {
+    fn base(&self) -> Option<&'static Interface> {
+        Some(IFACES[self.base?])
+    }
+
+    fn methods(&self) -> Result<&'static [Method], syn::Error> {
+        match self.methods {
+            Ok(methods) => Ok(methods),
+            Err(reason) => Err(syn::Error::new(
+                Span::call_site(),
+                format!(
+                    "Interface {} cannot be implemented in rust \
+                     because {} is not supported yet",
+                    self.name, reason
+                ),
+            )),
+        }
+    }
+}
+
+lazy_static! {
+    /// This item contains the information generated by the procedural macro in
+    /// the form of a `HashMap` from interface names to their descriptions.
+    static ref IFACES: HashMap<&'static str, &'static Interface> = {
+        let lists: &[&[Interface]] =
+            include!(mozbuild::objdir_path!("dist/xpcrs/bt/all.rs"));
+
+        let mut hm = HashMap::new();
+        for &list in lists {
+            for iface in list {
+                hm.insert(iface.name, iface);
+            }
+        }
+        hm
+    };
+}
+
+/// The type of the reference count to use for the struct.
+#[derive(Debug, Eq, PartialEq, Copy, Clone)]
+enum RefcntKind {
+    Atomic,
+    NonAtomic,
+}
+
+/// Produces the tokens for the type representation.
+impl ToTokens for RefcntKind {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        match *self {
+            RefcntKind::NonAtomic => quote!(xpcom::Refcnt).to_tokens(tokens),
+            RefcntKind::Atomic => quote!(xpcom::AtomicRefcnt).to_tokens(tokens),
+        }
+    }
+}
+
+/// Extract the fields list from the input struct.
+fn get_fields(si: &ItemStruct) -> Result<&Punctuated<Field, Token![,]>, syn::Error> {
+    match si.fields {
+        Fields::Named(ref named) => Ok(&named.named),
+        _ => bail!(@(si), "The initializer struct must be a standard named \
+                          value struct definition"),
+    }
+}
+
+/// Takes the template struct in, and generates `ItemStruct` for the "real" and
+/// "init" structs.
+fn gen_structs(
+    template: &ItemStruct,
+    bases: &[&Interface],
+    refcnt_ty: RefcntKind,
+) -> Result<(ItemStruct, ItemStruct), syn::Error> {
+    let real_ident = &template.ident;
+    let init_ident = format_ident!("Init{}", real_ident);
+    let vis = &template.vis;
+
+    let bases = bases.iter().map(|base| {
+        let ident = format_ident!("__base_{}", base.name);
+        let vtable = format_ident!("{}VTable", base.name);
+        quote!(#ident : &'static xpcom::interfaces::#vtable)
+    });
+
+    let fields = get_fields(template)?;
+    let (impl_generics, _, where_clause) = template.generics.split_for_impl();
+    Ok((
+        parse_quote! {
+           #[repr(C)]
+           #vis struct #real_ident #impl_generics #where_clause {
+               #(#bases,)*
+               __refcnt: #refcnt_ty,
+               #fields
+           }
+        },
+        parse_quote! {
+           #vis struct #init_ident #impl_generics #where_clause {
+               #fields
+           }
+        },
+    ))
+}
+
+/// Generates the `extern "system"` methods which are actually included in the
+/// VTable for the given interface.
+///
+/// `idx` must be the offset in pointers of the pointer to this vtable in the
+/// struct `real`. This is soundness-critical, as it will be used to offset
+/// pointers received from xpcom back to the concrete implementation.
+fn gen_vtable_methods(
+    real: &ItemStruct,
+    iface: &Interface,
+    vtable_index: usize,
+) -> Result<TokenStream, syn::Error> {
+    let base_ty = format_ident!("{}", iface.name);
+
+    let base_methods = if let Some(base) = iface.base() {
+        gen_vtable_methods(real, base, vtable_index)?
+    } else {
+        quote! {}
+    };
+
+    let ty_name = &real.ident;
+    let (impl_generics, ty_generics, where_clause) = real.generics.split_for_impl();
+
+    let mut method_defs = Vec::new();
+    for method in iface.methods()? {
+        let ret = syn::parse_str::<Type>(method.ret)?;
+
+        let mut params = Vec::new();
+        let mut args = Vec::new();
+        for param in method.params {
+            let name = format_ident!("{}", param.name);
+            let ty = syn::parse_str::<Type>(param.ty)?;
+
+            params.push(quote! {#name : #ty,});
+            args.push(quote! {#name,});
+        }
+
+        let name = format_ident!("{}", method.name);
+        method_defs.push(quote! {
+            unsafe extern "system" fn #name #impl_generics (
+                this: *const #base_ty, #(#params)*
+            ) -> #ret #where_clause {
+                let this: &#ty_name #ty_generics =
+                    ::xpcom::reexports::transmute_from_vtable_ptr(&this, #vtable_index);
+                this.#name(#(#args)*)
+            }
+        });
+    }
+
+    Ok(quote! {
+        #base_methods
+        #(#method_defs)*
+    })
+}
+
+/// Generates the VTable for a given base interface. This assumes that the
+/// implementations of each of the `extern "system"` methods are in scope.
+fn gen_inner_vtable(real: &ItemStruct, iface: &Interface) -> Result<TokenStream, syn::Error> {
+    let vtable_ty = format_ident!("{}VTable", iface.name);
+
+    // Generate the vtable for the base interface.
+    let base_vtable = if let Some(base) = iface.base() {
+        let vt = gen_inner_vtable(real, base)?;
+        quote! {__base: #vt,}
+    } else {
+        quote! {}
+    };
+
+    // Include each of the method definitions for this interface.
+    let (_, ty_generics, _) = real.generics.split_for_impl();
+    let turbofish = ty_generics.as_turbofish();
+    let vtable_init = iface
+        .methods()?
+        .iter()
+        .map(|method| {
+            let name = format_ident!("{}", method.name);
+            quote! { #name : #name #turbofish, }
+        })
+        .collect::<Vec<_>>();
+
+    Ok(quote!(#vtable_ty {
+        #base_vtable
+        #(#vtable_init)*
+    }))
+}
+
+fn gen_root_vtable(
+    real: &ItemStruct,
+    base: &Interface,
+    idx: usize,
+) -> Result<TokenStream, syn::Error> {
+    let field = format_ident!("__base_{}", base.name);
+    let vtable_ty = format_ident!("{}VTable", base.name);
+
+    let (impl_generics, ty_generics, where_clause) = real.generics.split_for_impl();
+    let turbofish = ty_generics.as_turbofish();
+
+    let methods = gen_vtable_methods(real, base, idx)?;
+    let vtable = gen_inner_vtable(real, base)?;
+
+    // Define the `recover_self` method. This performs an offset calculation to
+    // recover a pointer to the original struct from a pointer to the given
+    // VTable field.
+    Ok(quote! {#field: {
+        // The method implementations which will be used to build the vtable.
+        #methods
+
+        // The actual VTable definition. This is in a separate method in order
+        // to allow it to be generic.
+        #[inline]
+        fn get_vtable #impl_generics () -> &'static ::xpcom::reexports::VTableExtra<#vtable_ty> #where_clause {
+            &::xpcom::reexports::VTableExtra {
+                #[cfg(not(windows))]
+                offset: {
+                    // NOTE: workaround required to avoid depending on the
+                    // unstable const expression feature `const {}`.
+                    const OFFSET: isize = -((::std::mem::size_of::<usize>() * #idx) as isize);
+                    OFFSET
+                },
+                #[cfg(not(windows))]
+                typeinfo: 0 as *const _,
+                vtable: #vtable,
+            }
+        }
+        &get_vtable #turbofish ().vtable
+    },})
+}
+
+/// Generate the cast implementations. This generates the implementation details
+/// for the `Coerce` trait, and the `QueryInterface` method. The first return
+/// value is the `QueryInterface` implementation, and the second is the `Coerce`
+/// implementation.
+fn gen_casts(
+    seen: &mut HashSet<&'static str>,
+    iface: &Interface,
+    real: &ItemStruct,
+    coerce_name: &Ident,
+    vtable_field: &Ident,
+) -> Result<(TokenStream, TokenStream), syn::Error> {
+    if !seen.insert(iface.name) {
+        return Ok((quote! {}, quote! {}));
+    }
+
+    // Generate the cast implementations for the base interfaces.
+    let (base_qi, base_coerce) = if let Some(base) = iface.base() {
+        gen_casts(seen, base, real, coerce_name, vtable_field)?
+    } else {
+        (quote! {}, quote! {})
+    };
+
+    // Add the if statment to QueryInterface for the base class.
+    let base_name = format_ident!("{}", iface.name);
+
+    let qi = quote! {
+        #base_qi
+        if *uuid == #base_name::IID {
+            // Implement QueryInterface in terms of coercions.
+            self.addref();
+            *result = self.coerce::<#base_name>()
+                as *const #base_name
+                as *const ::xpcom::reexports::libc::c_void
+                as *mut ::xpcom::reexports::libc::c_void;
+            return ::xpcom::reexports::NS_OK;
+        }
+    };
+
+    // Add an implementation of the `*Coerce` trait for the base interface.
+    let name = &real.ident;
+    let (impl_generics, ty_generics, where_clause) = real.generics.split_for_impl();
+    let coerce = quote! {
+        #base_coerce
+
+        impl #impl_generics #coerce_name #ty_generics for ::xpcom::interfaces::#base_name #where_clause {
+            fn coerce_from(v: &#name #ty_generics) -> &Self {
+                unsafe {
+                    // Get the address of the VTable field. This should be a
+                    // pointer to a pointer to a vtable, which we can then cast
+                    // into a pointer to our interface.
+                    &*(&(v.#vtable_field)
+                        as *const &'static _
+                        as *const ::xpcom::interfaces::#base_name)
+                }
+            }
+        }
+    };
+
+    Ok((qi, coerce))
+}
+
+fn check_generics(generics: &syn::Generics) -> Result<(), syn::Error> {
+    for param in &generics.params {
+        let tp = match param {
+            syn::GenericParam::Type(tp) => tp,
+            syn::GenericParam::Lifetime(lp) => bail!(
+                @(lp),
+                "Cannot use #[xpcom] on types with lifetime parameters. \
+                Implementors of XPCOM interfaces must not contain non-'static \
+                lifetimes.",
+            ),
+            // XXX: Once const generics become stable, it may be as simple as
+            // removing this bail! to support them.
+            syn::GenericParam::Const(cp) => {
+                bail!(@(cp), "Cannot use #[xpcom] on types with const generics.")
+            }
+        };
+
+        let mut static_lt = false;
+        for bound in &tp.bounds {
+            match bound {
+                syn::TypeParamBound::Lifetime(lt) if lt.ident == "static" => {
+                    static_lt = true;
+                    break;
+                }
+                _ => {}
+            }
+        }
+
+        if !static_lt {
+            bail!(
+                @(param),
+                "Every generic parameter for xpcom implementation must have a \
+                'static lifetime bound declared in the generics. Implicit \
+                lifetime bounds or lifetime bounds in where clauses are not \
+                detected by the macro and will be ignored. \
+                Implementors of XPCOM interfaces must not contain non-'static \
+                lifetimes.",
+            );
+        }
+    }
+    Ok(())
+}
+
+#[derive(Default)]
+struct Options {
+    bases: Vec<&'static Interface>,
+    refcnt: Option<RefcntKind>,
+}
+
+impl Options {
+    fn parse(&mut self, meta: ParseNestedMeta) -> Result<(), syn::Error> {
+        if meta.path.is_ident("atomic") || meta.path.is_ident("nonatomic") {
+            if self.refcnt.is_some() {
+                bail!(@(meta.path), "Duplicate refcnt atomicity specifier");
+            }
+            self.refcnt = Some(if meta.path.is_ident("atomic") {
+                RefcntKind::Atomic
+            } else {
+                RefcntKind::NonAtomic
+            });
+            Ok(())
+        } else if meta.path.is_ident("implement") {
+            meta.parse_nested_meta(|meta| {
+                let ident = match meta.path.get_ident() {
+                    Some(ref iface) => iface.to_string(),
+                    _ => bail!(@(meta.path), "Interface name must be unqualified"),
+                };
+                if let Some(&iface) = IFACES.get(ident.as_str()) {
+                    self.bases.push(iface);
+                } else {
+                    bail!(@(meta.path), "Invalid base interface `{}`", ident);
+                }
+                Ok(())
+            })
+        } else {
+            bail!(@(meta.path), "Unexpected argument to #[xpcom]")
+        }
+    }
+
+    fn validate(self) -> Result<Self, syn::Error> {
+        if self.bases.is_empty() {
+            bail!(
+                "Types with #[xpcom(..)] must implement at least one \
+                interface. Interfaces can be implemented by adding an \
+                implements(nsIFoo, nsIBar) parameter to the #[xpcom] attribute"
+            );
+        }
+
+        if self.refcnt.is_none() {
+            bail!("Must specify refcnt kind in #[xpcom] attribute");
+        }
+
+        Ok(self)
+    }
+}
+
+/// The root xpcom procedural macro definition.
+fn xpcom_impl(options: Options, template: ItemStruct) -> Result<TokenStream, syn::Error> {
+    check_generics(&template.generics)?;
+
+    let bases = options.bases;
+
+    // Ensure that all our base interface methods have unique names.
+    let mut method_names = HashMap::new();
+    for base in &bases {
+        for method in base.methods()? {
+            if let Some(existing) = method_names.insert(method.name, base.name) {
+                bail!(
+                    "The method `{0}` is declared on both `{1}` and `{2}`,
+                     but a Rust type cannot implement two methods with the \
+                     same name. You can add the `[binaryname(Renamed{0})]` \
+                     XPIDL attribute to one of the declarations to rename it.",
+                    method.name,
+                    existing,
+                    base.name
+                );
+            }
+        }
+    }
+
+    // Determine what reference count type to use, and generate the real struct.
+    let refcnt_ty = options.refcnt.unwrap();
+    let (real, init) = gen_structs(&template, &bases, refcnt_ty)?;
+
+    let name_init = &init.ident;
+    let name = &real.ident;
+    let coerce_name = format_ident!("{}Coerce", name);
+
+    // Generate a VTable for each of the base interfaces.
+    let mut vtables = Vec::new();
+    for (idx, base) in bases.iter().enumerate() {
+        vtables.push(gen_root_vtable(&real, base, idx)?);
+    }
+
+    // Generate the field initializers for the final struct, moving each field
+    // out of the original __init struct.
+    let inits = get_fields(&init)?.iter().map(|field| {
+        let id = &field.ident;
+        quote! { #id : __init.#id, }
+    });
+
+    let vis = &real.vis;
+
+    // Generate the implementation for QueryInterface and Coerce.
+    let mut seen = HashSet::new();
+    let mut qi_impl = Vec::new();
+    let mut coerce_impl = Vec::new();
+    for base in &bases {
+        let (qi, coerce) = gen_casts(
+            &mut seen,
+            base,
+            &real,
+            &coerce_name,
+            &format_ident!("__base_{}", base.name),
+        )?;
+        qi_impl.push(qi);
+        coerce_impl.push(coerce);
+    }
+
+    let assert_sync = if bases.iter().any(|iface| iface.sync) {
+        quote! {
+            // Helper for asserting that for all instantiations, this
+            // object implements Send + Sync.
+            fn xpcom_type_must_be_send_sync<T: Send + Sync>(t: &T) {}
+            xpcom_type_must_be_send_sync(&*boxed);
+        }
+    } else {
+        quote! {}
+    };
+
+    let size_for_logs = if real.generics.params.is_empty() {
+        quote!(::std::mem::size_of::<Self>() as u32)
+    } else {
+        // Refcount logging requires all types with the same name to have the
+        // same size, and generics aren't taken into account when creating our
+        // name string, so we need to make sure that all possible instantiations
+        // report the same size. To do that, we fake a size based on the number
+        // of vtable pointers and the known refcount field.
+        let fake_size_npointers = bases.len() + 1;
+        quote!((::std::mem::size_of::<usize>() * #fake_size_npointers) as u32)
+    };
+
+    let (impl_generics, ty_generics, where_clause) = real.generics.split_for_impl();
+    let name_for_logs = quote!(
+        concat!(module_path!(), "::", stringify!(#name #ty_generics), "\0").as_ptr()
+            as *const ::xpcom::reexports::libc::c_char
+    );
+    Ok(quote! {
+        #init
+
+        #real
+
+        impl #impl_generics #name #ty_generics #where_clause {
+            /// This method is used for
+            fn allocate(__init: #name_init #ty_generics) -> ::xpcom::RefPtr<Self> {
+                #[allow(unused_imports)]
+                use ::xpcom::*;
+                #[allow(unused_imports)]
+                use ::xpcom::interfaces::*;
+                #[allow(unused_imports)]
+                use ::xpcom::reexports::{
+                    libc, nsACString, nsAString, nsCString, nsString, nsresult
+                };
+
+                // Helper for asserting that for all instantiations, this
+                // object has the 'static lifetime.
+                fn xpcom_types_must_be_static<T: 'static>(t: &T) {}
+
+                unsafe {
+                    // NOTE: This is split into multiple lines to make the
+                    // output more readable.
+                    let value = #name {
+                        #(#vtables)*
+                        __refcnt: #refcnt_ty::new(),
+                        #(#inits)*
+                    };
+                    let boxed = ::std::boxed::Box::new(value);
+                    xpcom_types_must_be_static(&*boxed);
+                    #assert_sync
+                    let raw = ::std::boxed::Box::into_raw(boxed);
+                    ::xpcom::RefPtr::from_raw(raw).unwrap()
+                }
+            }
+
+            /// Automatically generated implementation of AddRef for nsISupports.
+            #vis unsafe fn AddRef(&self) -> ::xpcom::MozExternalRefCountType {
+                let new = self.__refcnt.inc();
+                ::xpcom::trace_refcnt::NS_LogAddRef(
+                    self as *const _ as *mut ::xpcom::reexports::libc::c_void,
+                    new as usize,
+                    #name_for_logs,
+                    #size_for_logs,
+                );
+                new
+            }
+
+            /// Automatically generated implementation of Release for nsISupports.
+            #vis unsafe fn Release(&self) -> ::xpcom::MozExternalRefCountType {
+                let new = self.__refcnt.dec();
+                ::xpcom::trace_refcnt::NS_LogRelease(
+                    self as *const _ as *mut ::xpcom::reexports::libc::c_void,
+                    new as usize,
+                    #name_for_logs,
+                    #size_for_logs,
+                );
+                if new == 0 {
+                    // dealloc
+                    ::std::mem::drop(::std::boxed::Box::from_raw(self as *const Self as *mut Self));
+                }
+                new
+            }
+
+            /// Automatically generated implementation of QueryInterface for
+            /// nsISupports.
+            #vis unsafe fn QueryInterface(&self,
+                                          uuid: *const ::xpcom::nsIID,
+                                          result: *mut *mut ::xpcom::reexports::libc::c_void)
+                                          -> ::xpcom::reexports::nsresult {
+                #[allow(unused_imports)]
+                use ::xpcom::*;
+                #[allow(unused_imports)]
+                use ::xpcom::interfaces::*;
+
+                #(#qi_impl)*
+
+                ::xpcom::reexports::NS_ERROR_NO_INTERFACE
+            }
+
+            /// Perform a QueryInterface call on this object, attempting to
+            /// dynamically cast it to the requested interface type. Returns
+            /// Some(RefPtr<T>) if the cast succeeded, and None otherwise.
+            #vis fn query_interface<XPCOM_InterfaceType: ::xpcom::XpCom>(&self)
+                -> ::std::option::Option<::xpcom::RefPtr<XPCOM_InterfaceType>>
+            {
+                let mut ga = ::xpcom::GetterAddrefs::<XPCOM_InterfaceType>::new();
+                unsafe {
+                    if self.QueryInterface(&XPCOM_InterfaceType::IID, ga.void_ptr()).succeeded() {
+                        ga.refptr()
+                    } else {
+                        None
+                    }
+                }
+            }
+
+            /// Coerce this type safely to any of the interfaces which it
+            /// implements without `AddRef`ing it.
+            #vis fn coerce<XPCOM_InterfaceType: #coerce_name #ty_generics>(&self) -> &XPCOM_InterfaceType {
+                XPCOM_InterfaceType::coerce_from(self)
+            }
+        }
+
+        /// This trait is implemented on the interface types which this
+        /// `#[xpcom]` type can be safely ane cheaply coerced to using the
+        /// `coerce` method.
+        ///
+        /// The trait and its method should usually not be used directly, but
+        /// rather acts as a trait bound and implementation for the `coerce`
+        /// methods.
+        #[doc(hidden)]
+        #vis trait #coerce_name #impl_generics #where_clause {
+            /// Convert a value of the `#[xpcom]` type into the implementing
+            /// interface type.
+            fn coerce_from(v: &#name #ty_generics) -> &Self;
+        }
+
+        #(#coerce_impl)*
+
+        unsafe impl #impl_generics ::xpcom::RefCounted for #name #ty_generics #where_clause {
+            unsafe fn addref(&self) {
+                self.AddRef();
+            }
+
+            unsafe fn release(&self) {
+                self.Release();
+            }
+        }
+    })
+}
+
+#[proc_macro_attribute]
+pub fn xpcom(
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let mut options = Options::default();
+    let xpcom_parser = syn::meta::parser(|meta| options.parse(meta));
+    parse_macro_input!(args with xpcom_parser);
+    let input = parse_macro_input!(input as ItemStruct);
+    match options
+        .validate()
+        .and_then(|options| xpcom_impl(options, input))
+    {
+        Ok(ts) => ts.into(),
+        Err(err) => err.to_compile_error().into(),
+    }
+}