rust/fbthrift_ext/adapters: RFC: add UsizeAdapter

Summary: Adding a thrift adapter for `usize`, similar to those for the explicitly sized unsigned integer types. Only implementing it for 64-bit platforms for now, but this can be trivially extended if/when needed

Reviewed By: Imxset21

Differential Revision: D66657692

fbshipit-source-id: 69f1aa836ddf9b74e881e5cfdfb2a8efc6793a52

shed/fbthrift_ext/adapters/lib.rs

@@ -121,5 +121,8 @@ pub use crate::redacted::RedactedAdapter;
 pub use crate::socket_addr::SocketAddrAdapter;
 #[doc(inline)]
 pub use crate::unsigned_int::UnsignedIntAdapter;
+#[cfg(target_pointer_width = "64")]
+#[doc(inline)]
+pub use crate::unsigned_int::UsizeAdapter;
 #[doc(inline)]
 pub use crate::uuid::UuidAdapter;

shed/fbthrift_ext/adapters/unsigned_int.rs

@@ -30,8 +30,8 @@ use fbthrift::adapter::ThriftAdapter;
 pub struct UnsignedIntAdapter<T>(PhantomData<T>);
 
 macro_rules! unsigned_int_adapter {
-    ($thrift:ty, $rust:ty) => {
-        impl ThriftAdapter for UnsignedIntAdapter<$thrift> {
+    ($thrift:ty, $rust:ty, $adapter:ty) => {
+        impl ThriftAdapter for $adapter {
             type StandardType = $thrift;
             type AdaptedType = $rust;
             type Error = std::convert::Infallible;
@@ -47,7 +47,27 @@ macro_rules! unsigned_int_adapter {
     };
 }
 
-unsigned_int_adapter!(i8, u8);
-unsigned_int_adapter!(i16, u16);
-unsigned_int_adapter!(i32, u32);
-unsigned_int_adapter!(i64, u64);
+unsigned_int_adapter!(i8, u8, UnsignedIntAdapter<i8>);
+unsigned_int_adapter!(i16, u16, UnsignedIntAdapter<i16>);
+unsigned_int_adapter!(i32, u32, UnsignedIntAdapter<i32>);
+unsigned_int_adapter!(i64, u64, UnsignedIntAdapter<i64>);
+
+#[cfg(target_pointer_width = "64")]
+/// Adapts the platform-appropriate signed Thrift integer type to `usize`
+///
+/// # Examples
+///
+/// ```thrift
+/// include "thrift/annotation/rust.thrift";
+///
+/// @rust.Adapter{name = "::fbthrift_adapters::UsizeAdapter"}
+/// typedef i64 Usize;
+///
+/// struct Parameters {
+///   1: Usize my_param;
+/// }
+/// ```
+pub struct UsizeAdapter(PhantomData<i64>);
+
+#[cfg(target_pointer_width = "64")]
+unsigned_int_adapter!(i64, usize, UsizeAdapter);