1 files changed, 52 insertions, 0 deletions
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,
+}