[WIP] standalone proc_macro backend

library/proc_macro/src/bridge/client.rs

@@ -5,6 +5,9 @@ use std::marker::PhantomData;
 use std::sync::atomic::AtomicU32;
 
 use super::*;
+use crate::StandaloneLevel;
+use crate::bridge::server::{Dispatcher, DispatcherTrait};
+use crate::bridge::standalone::NoRustc;
 
 macro_rules! define_client_handles {
     (
@@ -141,7 +144,10 @@ macro_rules! define_client_side {
                     api_tags::Method::$name(api_tags::$name::$method).encode(&mut buf, &mut ());
                     $($arg.encode(&mut buf, &mut ());)*
 
-                    buf = bridge.dispatch.call(buf);
+                    buf = match &mut bridge.dispatch {
+                        DispatchWay::Closure(f) => f.call(buf),
+                        DispatchWay::Directly(disp) => disp.dispatch(buf),
+                    };
 
                     let r = Result::<_, PanicMessage>::decode(&mut &buf[..], &mut ());
 
@@ -155,13 +161,18 @@ macro_rules! define_client_side {
 }
 with_api!(self, self, define_client_side);
 
+enum DispatchWay<'a> {
+    Closure(closure::Closure<'a, Buffer, Buffer>),
+    Directly(Dispatcher<NoRustc>),
+}
+
 struct Bridge<'a> {
     /// Reusable buffer (only `clear`-ed, never shrunk), primarily
     /// used for making requests.
     cached_buffer: Buffer,
 
     /// Server-side function that the client uses to make requests.
-    dispatch: closure::Closure<'a, Buffer, Buffer>,
+    dispatch: DispatchWay<'a>,
 
     /// Provided globals for this macro expansion.
     globals: ExpnGlobals<Span>,
@@ -173,12 +184,33 @@ impl<'a> !Sync for Bridge<'a> {}
 #[allow(unsafe_code)]
 mod state {
     use std::cell::{Cell, RefCell};
+    use std::marker::PhantomData;
     use std::ptr;
 
     use super::Bridge;
+    use crate::StandaloneLevel;
+    use crate::bridge::buffer::Buffer;
+    use crate::bridge::client::{COUNTERS, DispatchWay};
+    use crate::bridge::server::{Dispatcher, HandleStore, MarkedTypes};
+    use crate::bridge::{ExpnGlobals, Marked, standalone};
 
     thread_local! {
         static BRIDGE_STATE: Cell<*const ()> = const { Cell::new(ptr::null()) };
+        static STANDALONE: RefCell<Bridge<'static>> = RefCell::new(standalone_bridge());
+        pub(super) static USE_STANDALONE: Cell<StandaloneLevel> = const { Cell::new(StandaloneLevel::Never) };
+    }
+
+    fn standalone_bridge() -> Bridge<'static> {
+        let mut store = HandleStore::new(&COUNTERS);
+        let id = store.Span.alloc(Marked { value: standalone::Span::DUMMY, _marker: PhantomData });
+        let dummy = super::Span { handle: id };
+        let dispatcher =
+            Dispatcher { handle_store: store, server: MarkedTypes(standalone::NoRustc) };
+        Bridge {
+            cached_buffer: Buffer::new(),
+            dispatch: DispatchWay::Directly(dispatcher),
+            globals: ExpnGlobals { call_site: dummy, def_site: dummy, mixed_site: dummy },
+        }
     }
 
     pub(super) fn set<'bridge, R>(state: &RefCell<Bridge<'bridge>>, f: impl FnOnce() -> R) -> R {
@@ -199,16 +231,23 @@ mod state {
     pub(super) fn with<R>(
         f: impl for<'bridge> FnOnce(Option<&RefCell<Bridge<'bridge>>>) -> R,
     ) -> R {
-        let state = BRIDGE_STATE.get();
-        // SAFETY: the only place where the pointer is set is in `set`. It puts
-        // back the previous value after the inner call has returned, so we know
-        // that as long as the pointer is not null, it came from a reference to
-        // a `RefCell<Bridge>` that outlasts the call to this function. Since `f`
-        // works the same for any lifetime of the bridge, including the actual
-        // one, we can lie here and say that the lifetime is `'static` without
-        // anyone noticing.
-        let bridge = unsafe { state.cast::<RefCell<Bridge<'static>>>().as_ref() };
-        f(bridge)
+        let level = USE_STANDALONE.get();
+        if level == StandaloneLevel::Always
+            || (level == StandaloneLevel::FallbackOnly && BRIDGE_STATE.get().is_null())
+        {
+            STANDALONE.with(|bridge| f(Some(bridge)))
+        } else {
+            let state = BRIDGE_STATE.get();
+            // SAFETY: the only place where the pointer is set is in `set`. It puts
+            // back the previous value after the inner call has returned, so we know
+            // that as long as the pointer is not null, it came from a reference to
+            // a `RefCell<Bridge>` that outlasts the call to this function. Since `f`
+            // works the same for any lifetime of the bridge, including the actual
+            // one, we can lie here and say that the lifetime is `'static` without
+            // anyone noticing.
+            let bridge = unsafe { state.cast::<RefCell<Bridge<'static>>>().as_ref() };
+            f(bridge)
+        }
     }
 }
 
@@ -228,6 +267,10 @@ pub(crate) fn is_available() -> bool {
     state::with(|s| s.is_some())
 }
 
+pub(crate) fn enable_standalone(level: StandaloneLevel) {
+    state::USE_STANDALONE.set(level);
+}
+
 /// A client-side RPC entry-point, which may be using a different `proc_macro`
 /// from the one used by the server, but can be invoked compatibly.
 ///
@@ -292,7 +335,11 @@ fn run_client<A: for<'a, 's> Decode<'a, 's, ()>, R: Encode<()>>(
         let (globals, input) = <(ExpnGlobals<Span>, A)>::decode(reader, &mut ());
 
         // Put the buffer we used for input back in the `Bridge` for requests.
-        let state = RefCell::new(Bridge { cached_buffer: buf.take(), dispatch, globals });
+        let state = RefCell::new(Bridge {
+            cached_buffer: buf.take(),
+            dispatch: DispatchWay::Closure(dispatch),
+            globals,
+        });
 
         let output = state::set(&state, || f(input));
 

library/proc_macro/src/bridge/mod.rs

@@ -138,6 +138,7 @@ mod rpc;
 mod selfless_reify;
 #[forbid(unsafe_code)]
 pub mod server;
+pub(crate) mod standalone;
 #[allow(unsafe_code)]
 mod symbol;
 

library/proc_macro/src/bridge/server.rs

@@ -12,12 +12,12 @@ macro_rules! define_server_handles {
     ) => {
         #[allow(non_snake_case)]
         pub(super) struct HandleStore<S: Types> {
-            $($oty: handle::OwnedStore<S::$oty>,)*
-            $($ity: handle::InternedStore<S::$ity>,)*
+            $(pub(super) $oty: handle::OwnedStore<S::$oty>,)*
+            $(pub(super) $ity: handle::InternedStore<S::$ity>,)*
         }
 
         impl<S: Types> HandleStore<S> {
-            fn new(handle_counters: &'static client::HandleCounters) -> Self {
+            pub(super) fn new(handle_counters: &'static client::HandleCounters) -> Self {
                 HandleStore {
                     $($oty: handle::OwnedStore::new(&handle_counters.$oty),)*
                     $($ity: handle::InternedStore::new(&handle_counters.$ity),)*
@@ -119,7 +119,7 @@ macro_rules! declare_server_traits {
 }
 with_api!(Self, self_, declare_server_traits);
 
-pub(super) struct MarkedTypes<S: Types>(S);
+pub(super) struct MarkedTypes<S: Types>(pub(super) S);
 
 impl<S: Server> Server for MarkedTypes<S> {
     fn globals(&mut self) -> ExpnGlobals<Self::Span> {
@@ -150,9 +150,9 @@ macro_rules! define_mark_types_impls {
 }
 with_api!(Self, self_, define_mark_types_impls);
 
-struct Dispatcher<S: Types> {
-    handle_store: HandleStore<S>,
-    server: S,
+pub(super) struct Dispatcher<S: Types> {
+    pub(super) handle_store: HandleStore<MarkedTypes<S>>,
+    pub(super) server: MarkedTypes<S>,
 }
 
 macro_rules! define_dispatcher_impl {
@@ -167,7 +167,7 @@ macro_rules! define_dispatcher_impl {
             fn dispatch(&mut self, buf: Buffer) -> Buffer;
         }
 
-        impl<S: Server> DispatcherTrait for Dispatcher<MarkedTypes<S>> {
+        impl<S: Server> DispatcherTrait for Dispatcher<S> {
             $(type $name = <MarkedTypes<S> as Types>::$name;)*
 
             fn dispatch(&mut self, mut buf: Buffer) -> Buffer {