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ffi: Add new conversion trait CallbackResultTypeInfo

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For the most part we'll reuse SimpleArgTypeInfo implementations, but
that doesn't cover everything we currently do with callbacks in the C
bridge. This trait will help /bridge/ the gap in converting more
callback traits to use #[bridge_callbacks].
This commit is contained in:
Jordan Rose 2025-12-18 17:42:09 -08:00
parent 50e2743229
commit 81e47eb31c
1 changed files with 39 additions and 1 deletions
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40
rust/bridge/shared/types/src/ffi/convert.rs
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@ -109,10 +109,35 @@ where
}
}
/// A variation of [`ArgTypeInfo`] for callback results.
///
/// All [`SimpleArgTypeInfo`] implementations are reusable for this, but the general [`ArgTypeInfo`]
/// allows borrowing from the foreign value and a callback result can't do that.
pub trait CallbackResultTypeInfo: Sized {
/// The FFI form of the argument (e.g. `std::ffi::c_uchar`).
type ResultType;
/// Converts the data in `foreign` to the Rust type.
fn convert_from_callback(foreign: Self::ResultType) -> SignalFfiResult<Self>;
}
impl<T: SimpleArgTypeInfo> CallbackResultTypeInfo for T {
type ResultType = <Self as SimpleArgTypeInfo>::ArgType;
fn convert_from_callback(foreign: Self::ResultType) -> SignalFfiResult<Self> {
T::convert_from(foreign)
}
}
impl CallbackResultTypeInfo for () {
type ResultType = std::ffi::c_void;
fn convert_from_callback(_foreign: Self::ResultType) -> SignalFfiResult<Self> {
Ok(())
}
}
/// Converts result values from their Rust form to their FFI form.
///
/// `ResultTypeInfo` is used to implement the `bridge_fn` macro, but can also be used outside it.
/// `ResultTypeInfo` is also used for callback arguments in the `bridge_callback` macro.
///
/// ```
/// # use libsignal_bridge_types::ffi::*;
@ -1180,6 +1205,19 @@ macro_rules! ffi_bridge_as_handle {
( $typ:ty as false $(, $($_:tt)*)? ) => {};
( $typ:ty as $ffi_name:ident ) => {
impl $crate::ffi::BridgeHandle for $typ {}
// Unfortunately this conflicts with the blanket impl for the trait if done generically.
impl $crate::ffi::CallbackResultTypeInfo for $typ {
type ResultType = $crate::ffi::MutPointer<$typ>;
fn convert_from_callback(
foreign: Self::ResultType,
) -> $crate::ffi::SignalFfiResult<Self> {
let foreign = foreign.into_inner();
if foreign.is_null() {
return Err($crate::ffi::NullPointerError.into());
}
Ok(unsafe { *Box::from_raw(foreign) })
}
}
};
( $typ:ty ) => {
::paste::paste! {