path: root/xpcom/rust/xpcom/xpcom_macros/src/lib.rs

/* 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::punctuated::Punctuated;
use syn::{
    parse_macro_input, parse_quote, AttributeArgs, Field, Fields, Ident, ItemStruct, Meta,
    MetaList, NestedMeta, Path, 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>,
    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 : *const 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()?
        .into_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 *const _
                        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_path_arg(&mut self, path: &Path) -> Result<(), syn::Error> {
        if path.is_ident("atomic") || path.is_ident("nonatomic") {
            if self.refcnt.is_some() {
                bail!(@(path), "Duplicate refcnt atomicity specifier");
            }
            self.refcnt = Some(if path.is_ident("atomic") {
                RefcntKind::Atomic
            } else {
                RefcntKind::NonAtomic
            });
            return Ok(());
        }
        bail!(@(path), "Unexpected path argument to #[xpcom]");
    }

    fn parse_list_arg(&mut self, list: &MetaList) -> Result<(), syn::Error> {
        if list.path.is_ident("implement") {
            for item in list.nested.iter() {
                let iface = match *item {
                    NestedMeta::Meta(syn::Meta::Path(ref iface)) => iface,
                    _ => bail!(@(item), "Expected interface name to implement"),
                };
                let ident = match iface.get_ident() {
                    Some(ref iface) => iface.to_string(),
                    _ => bail!(@(iface), "Interface name must be unqualified"),
                };
                if let Some(&iface) = IFACES.get(ident.as_str()) {
                    self.bases.push(iface);
                } else {
                    bail!(@(item), "Invalid base interface `{}`", ident);
                }
            }
            return Ok(());
        }
        bail!(@(list), "Unexpected list argument to #[xpcom]");
    }

    fn parse(&mut self, args: &AttributeArgs) -> Result<(), syn::Error> {
        for arg in args {
            match arg {
                NestedMeta::Meta(Meta::Path(path)) => self.parse_path_arg(path)?,
                NestedMeta::Meta(Meta::List(list)) => self.parse_list_arg(list)?,
                NestedMeta::Meta(Meta::NameValue(name_value)) => {
                    bail!(@(name_value), "Unexpected name-value argument to #[xpcom]")
                }
                NestedMeta::Lit(lit) => bail!(@(lit), "Unexpected literal argument to #[xpcom]"),
            }
        }

        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(())
    }
}

/// The root xpcom procedural macro definition.
fn xpcom_impl(args: AttributeArgs, template: ItemStruct) -> Result<TokenStream, syn::Error> {
    let mut options = Options::default();
    options.parse(&args)?;

    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 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);
                    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 args = parse_macro_input!(args as AttributeArgs);
    let input = parse_macro_input!(input as ItemStruct);
    match xpcom_impl(args, input) {
        Ok(ts) => ts.into(),
        Err(err) => err.to_compile_error().into(),
    }
}