diff --git a/library/proc_macro/src/bridge/client.rs b/library/proc_macro/src/bridge/client.rs
index cdb2bac260757..144de5822c50c 100644
--- a/library/proc_macro/src/bridge/client.rs
+++ b/library/proc_macro/src/bridge/client.rs
@@ -2,6 +2,7 @@
 
 use super::*;
 
+use std::cell::Cell;
 use std::marker::PhantomData;
 
 macro_rules! define_handles {
@@ -256,7 +257,7 @@ macro_rules! define_client_side {
                     api_tags::Method::$name(api_tags::$name::$method).encode(&mut b, &mut ());
                     reverse_encode!(b; $($arg),*);
 
-                    b = bridge.dispatch.call(b);
+                    b = (bridge.dispatch)(b);
 
                     let r = Result::<_, PanicMessage>::decode(&mut &b[..], &mut ());
 
@@ -270,48 +271,64 @@ macro_rules! define_client_side {
 }
 with_api!(self, self, define_client_side);
 
-enum BridgeState<'a> {
+enum BridgeState {
     /// No server is currently connected to this client.
     NotConnected,
 
     /// A server is connected and available for requests.
-    Connected(Bridge<'a>),
+    Connected(Bridge),
 
     /// Access to the bridge is being exclusively acquired
     /// (e.g., during `BridgeState::with`).
     InUse,
 }
 
-enum BridgeStateL {}
+impl BridgeState {
+    /// Sets the thread-local `BridgeState` to `replacement` while
+    /// running `f`, which gets the old `BridgeState`, mutably.
+    ///
+    /// The state will be restored after `f` exits, even
+    /// by panic, including modifications made to it by `f`.
+    fn replace_during<R>(replacement: Self, f: impl FnOnce(&mut Self) -> R) -> R {
+        /// Wrapper that ensures that a cell always gets filled
+        /// (with the original state, optionally changed by `f`),
+        /// even if `f` had panicked.
+        struct PutBackOnDrop<'a, T> {
+            cell: &'a Cell<T>,
+            value: Option<T>,
+        }
 
-impl<'a> scoped_cell::ApplyL<'a> for BridgeStateL {
-    type Out = BridgeState<'a>;
-}
+        impl<'a, T> Drop for PutBackOnDrop<'a, T> {
+            fn drop(&mut self) {
+                self.cell.set(self.value.take().unwrap());
+            }
+        }
 
-thread_local! {
-    static BRIDGE_STATE: scoped_cell::ScopedCell<BridgeStateL> =
-        scoped_cell::ScopedCell::new(BridgeState::NotConnected);
-}
+        thread_local! {
+            static BRIDGE_STATE: Cell<BridgeState> = Cell::new(BridgeState::NotConnected);
+        }
+        BRIDGE_STATE.with(|state| {
+            let mut put_back_on_drop =
+                PutBackOnDrop { cell: state, value: Some(state.replace(replacement)) };
+
+            f(put_back_on_drop.value.as_mut().unwrap())
+        })
+    }
 
-impl BridgeState<'_> {
     /// Take exclusive control of the thread-local
     /// `BridgeState`, and pass it to `f`, mutably.
+    ///
     /// The state will be restored after `f` exits, even
     /// by panic, including modifications made to it by `f`.
     ///
     /// N.B., while `f` is running, the thread-local state
     /// is `BridgeState::InUse`.
-    fn with<R>(f: impl FnOnce(&mut BridgeState<'_>) -> R) -> R {
-        BRIDGE_STATE.with(|state| {
-            state.replace(BridgeState::InUse, |mut state| {
-                // FIXME(#52812) pass `f` directly to `replace` when `RefMutL` is gone
-                f(&mut *state)
-            })
-        })
+    fn with<R>(f: impl FnOnce(&mut Self) -> R) -> R {
+        Self::replace_during(BridgeState::InUse, f)
     }
 }
 
-impl Bridge<'_> {
+impl Bridge {
     pub(crate) fn is_available() -> bool {
         BridgeState::with(|state| match state {
             BridgeState::Connected(_) | BridgeState::InUse => true,
@@ -337,10 +354,10 @@ impl Bridge<'_> {
             }));
         });
 
-        BRIDGE_STATE.with(|state| state.set(BridgeState::Connected(self), f))
+        BridgeState::replace_during(BridgeState::Connected(self), |_| f())
     }
 
-    fn with<R>(f: impl FnOnce(&mut Bridge<'_>) -> R) -> R {
+    fn with<R>(f: impl FnOnce(&mut Self) -> R) -> R {
         BridgeState::with(|state| match state {
             BridgeState::NotConnected => {
                 panic!("procedural macro API is used outside of a procedural macro");
@@ -367,7 +384,7 @@ pub struct Client<F> {
     // FIXME(eddyb) use a reference to the `static COUNTERS`, instead of
     // a wrapper `fn` pointer, once `const fn` can reference `static`s.
     pub(super) get_handle_counters: extern "C" fn() -> &'static HandleCounters,
-    pub(super) run: extern "C" fn(Bridge<'_>, F) -> Buffer<u8>,
+    pub(super) run: extern "C" fn(Bridge, F) -> Buffer<u8>,
     pub(super) f: F,
 }
 
@@ -375,7 +392,7 @@ pub struct Client<F> {
 /// deserializing input and serializing output.
 // FIXME(eddyb) maybe replace `Bridge::enter` with this?
 fn run_client<A: for<'a, 's> DecodeMut<'a, 's, ()>, R: Encode<()>>(
-    mut bridge: Bridge<'_>,
+    mut bridge: Bridge,
     f: impl FnOnce(A) -> R,
 ) -> Buffer<u8> {
     // The initial `cached_buffer` contains the input.
@@ -418,7 +435,7 @@ fn run_client<A: for<'a, 's> DecodeMut<'a, 's, ()>, R: Encode<()>>(
 impl Client<fn(crate::TokenStream) -> crate::TokenStream> {
     pub const fn expand1(f: fn(crate::TokenStream) -> crate::TokenStream) -> Self {
         extern "C" fn run(
-            bridge: Bridge<'_>,
+            bridge: Bridge,
             f: impl FnOnce(crate::TokenStream) -> crate::TokenStream,
         ) -> Buffer<u8> {
             run_client(bridge, |input| f(crate::TokenStream(input)).0)
@@ -432,7 +449,7 @@ impl Client<fn(crate::TokenStream, crate::TokenStream) -> crate::TokenStream> {
         f: fn(crate::TokenStream, crate::TokenStream) -> crate::TokenStream,
     ) -> Self {
         extern "C" fn run(
-            bridge: Bridge<'_>,
+            bridge: Bridge,
             f: impl FnOnce(crate::TokenStream, crate::TokenStream) -> crate::TokenStream,
         ) -> Buffer<u8> {
             run_client(bridge, |(input, input2)| {
diff --git a/library/proc_macro/src/bridge/closure.rs b/library/proc_macro/src/bridge/closure.rs
deleted file mode 100644
index 06f76d2fc9140..0000000000000
--- a/library/proc_macro/src/bridge/closure.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-//! Closure type (equivalent to `&mut dyn FnMut(A) -> R`) that's `repr(C)`.
-
-use std::marker::PhantomData;
-
-#[repr(C)]
-pub struct Closure<'a, A, R> {
-    call: unsafe extern "C" fn(*mut Env, A) -> R,
-    env: *mut Env,
-    // Ensure Closure is !Send and !Sync
-    _marker: PhantomData<*mut &'a mut ()>,
-}
-
-struct Env;
-
-impl<'a, A, R, F: FnMut(A) -> R> From<&'a mut F> for Closure<'a, A, R> {
-    fn from(f: &'a mut F) -> Self {
-        unsafe extern "C" fn call<A, R, F: FnMut(A) -> R>(env: *mut Env, arg: A) -> R {
-            (*(env as *mut _ as *mut F))(arg)
-        }
-        Closure { call: call::<A, R, F>, env: f as *mut _ as *mut Env, _marker: PhantomData }
-    }
-}
-
-impl<'a, A, R> Closure<'a, A, R> {
-    pub fn call(&mut self, arg: A) -> R {
-        unsafe { (self.call)(self.env, arg) }
-    }
-}
diff --git a/library/proc_macro/src/bridge/mod.rs b/library/proc_macro/src/bridge/mod.rs
index f7c9df6564f87..0368a4f2243c9 100644
--- a/library/proc_macro/src/bridge/mod.rs
+++ b/library/proc_macro/src/bridge/mod.rs
@@ -199,8 +199,6 @@ macro_rules! reverse_decode {
 mod buffer;
 #[forbid(unsafe_code)]
 pub mod client;
-#[allow(unsafe_code)]
-mod closure;
 #[forbid(unsafe_code)]
 mod handle;
 #[macro_use]
@@ -221,13 +219,13 @@ use rpc::{Decode, DecodeMut, Encode, Reader, Writer};
 /// field of `client::Client`. The client holds its copy of the `Bridge`
 /// in TLS during its execution (`Bridge::{enter, with}` in `client.rs`).
 #[repr(C)]
-pub struct Bridge<'a> {
+pub struct Bridge {
     /// Reusable buffer (only `clear`-ed, never shrunk), primarily
     /// used for making requests, but also for passing input to client.
     cached_buffer: Buffer<u8>,
 
     /// Server-side function that the client uses to make requests.
-    dispatch: closure::Closure<'a, Buffer<u8>, Buffer<u8>>,
+    dispatch: extern "C" fn(Buffer<u8>) -> Buffer<u8>,
 
     /// If 'true', always invoke the default panic hook
     force_show_panics: bool,
diff --git a/library/proc_macro/src/bridge/scoped_cell.rs b/library/proc_macro/src/bridge/scoped_cell.rs
index 2cde1f65adf9c..99d3c468b1c7d 100644
--- a/library/proc_macro/src/bridge/scoped_cell.rs
+++ b/library/proc_macro/src/bridge/scoped_cell.rs
@@ -41,9 +41,10 @@ impl<T: LambdaL> ScopedCell<T> {
 
     /// Sets the value in `self` to `replacement` while
     /// running `f`, which gets the old value, mutably.
+    ///
     /// The old value will be restored after `f` exits, even
     /// by panic, including modifications made to it by `f`.
-    pub fn replace<'a, R>(
+    pub fn replace_during<'a, R>(
         &self,
         replacement: <T as ApplyL<'a>>::Out,
         f: impl for<'b, 'c> FnOnce(RefMutL<'b, 'c, T>) -> R,
@@ -76,6 +77,6 @@ impl<T: LambdaL> ScopedCell<T> {
 
     /// Sets the value in `self` to `value` while running `f`.
     pub fn set<R>(&self, value: <T as ApplyL<'_>>::Out, f: impl FnOnce() -> R) -> R {
-        self.replace(value, |_| f())
+        self.replace_during(value, |_| f())
     }
 }
diff --git a/library/proc_macro/src/bridge/server.rs b/library/proc_macro/src/bridge/server.rs
index 2e0400d32a0af..185b9c9377efd 100644
--- a/library/proc_macro/src/bridge/server.rs
+++ b/library/proc_macro/src/bridge/server.rs
@@ -85,14 +85,16 @@ macro_rules! define_dispatcher_impl {
     ($($name:ident {
         $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
     }),* $(,)?) => {
-        // FIXME(eddyb) `pub` only for `ExecutionStrategy` below.
-        pub trait DispatcherTrait {
-            // HACK(eddyb) these are here to allow `Self::$name` to work below.
+        // HACK(eddyb) only a (private) trait because inherent impls can't have
+        // associated types (and `Self::AssocType` is used within `$arg_ty`).
+        // While `with_api!` allows customizing `Self`, it would have to be
+        // extended to allow `Self::` to become `<MarkedTypes<S> as Types>::`.
+        trait DispatcherPrivateHelperTrait {
             $(type $name;)*
             fn dispatch(&mut self, b: Buffer<u8>) -> Buffer<u8>;
         }
 
-        impl<S: Server> DispatcherTrait for Dispatcher<MarkedTypes<S>> {
+        impl<S: Server> DispatcherPrivateHelperTrait for Dispatcher<MarkedTypes<S>> {
             $(type $name = <MarkedTypes<S> as Types>::$name;)*
             fn dispatch(&mut self, mut b: Buffer<u8>) -> Buffer<u8> {
                 let Dispatcher { handle_store, server } = self;
@@ -128,39 +130,27 @@ macro_rules! define_dispatcher_impl {
 }
 with_api!(Self, self_, define_dispatcher_impl);
 
+// FIXME(eddyb) a trait alias of `FnMut(Buffer<u8>) -> Buffer<u8>` would allow
+// replacing the non-dynamic mentions of that trait, as well.
+pub type DynDispatch<'a> = &'a mut dyn FnMut(Buffer<u8>) -> Buffer<u8>;
+
 pub trait ExecutionStrategy {
-    fn run_bridge_and_client<D: Copy + Send + 'static>(
+    fn cross_thread_dispatch(
         &self,
-        dispatcher: &mut impl DispatcherTrait,
-        input: Buffer<u8>,
-        run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
-        client_data: D,
-        force_show_panics: bool,
+        server_thread_dispatch: impl FnMut(Buffer<u8>) -> Buffer<u8>,
+        with_client_thread_dispatch: impl FnOnce(DynDispatch<'_>) -> Buffer<u8> + Send + 'static,
     ) -> Buffer<u8>;
 }
 
 pub struct SameThread;
 
 impl ExecutionStrategy for SameThread {
-    fn run_bridge_and_client<D: Copy + Send + 'static>(
+    fn cross_thread_dispatch(
         &self,
-        dispatcher: &mut impl DispatcherTrait,
-        input: Buffer<u8>,
-        run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
-        client_data: D,
-        force_show_panics: bool,
+        mut server_thread_dispatch: impl FnMut(Buffer<u8>) -> Buffer<u8>,
+        with_client_thread_dispatch: impl FnOnce(DynDispatch<'_>) -> Buffer<u8> + Send + 'static,
     ) -> Buffer<u8> {
-        let mut dispatch = |b| dispatcher.dispatch(b);
-
-        run_client(
-            Bridge {
-                cached_buffer: input,
-                dispatch: (&mut dispatch).into(),
-                force_show_panics,
-                _marker: marker::PhantomData,
-            },
-            client_data,
-        )
+        with_client_thread_dispatch(&mut server_thread_dispatch)
     }
 }
 
@@ -170,13 +160,10 @@ impl ExecutionStrategy for SameThread {
 pub struct CrossThread1;
 
 impl ExecutionStrategy for CrossThread1 {
-    fn run_bridge_and_client<D: Copy + Send + 'static>(
+    fn cross_thread_dispatch(
         &self,
-        dispatcher: &mut impl DispatcherTrait,
-        input: Buffer<u8>,
-        run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
-        client_data: D,
-        force_show_panics: bool,
+        mut server_thread_dispatch: impl FnMut(Buffer<u8>) -> Buffer<u8>,
+        with_client_thread_dispatch: impl FnOnce(DynDispatch<'_>) -> Buffer<u8> + Send + 'static,
     ) -> Buffer<u8> {
         use std::sync::mpsc::channel;
 
@@ -184,24 +171,14 @@ impl ExecutionStrategy for CrossThread1 {
         let (res_tx, res_rx) = channel();
 
         let join_handle = thread::spawn(move || {
-            let mut dispatch = |b| {
+            with_client_thread_dispatch(&mut |b| {
                 req_tx.send(b).unwrap();
                 res_rx.recv().unwrap()
-            };
-
-            run_client(
-                Bridge {
-                    cached_buffer: input,
-                    dispatch: (&mut dispatch).into(),
-                    force_show_panics,
-                    _marker: marker::PhantomData,
-                },
-                client_data,
-            )
+            })
         });
 
         for b in req_rx {
-            res_tx.send(dispatcher.dispatch(b)).unwrap();
+            res_tx.send(server_thread_dispatch(b)).unwrap();
         }
 
         join_handle.join().unwrap()
@@ -211,13 +188,10 @@ impl ExecutionStrategy for CrossThread1 {
 pub struct CrossThread2;
 
 impl ExecutionStrategy for CrossThread2 {
-    fn run_bridge_and_client<D: Copy + Send + 'static>(
+    fn cross_thread_dispatch(
         &self,
-        dispatcher: &mut impl DispatcherTrait,
-        input: Buffer<u8>,
-        run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
-        client_data: D,
-        force_show_panics: bool,
+        mut server_thread_dispatch: impl FnMut(Buffer<u8>) -> Buffer<u8>,
+        with_client_thread_dispatch: impl FnOnce(DynDispatch<'_>) -> Buffer<u8> + Send + 'static,
     ) -> Buffer<u8> {
         use std::sync::{Arc, Mutex};
 
@@ -231,7 +205,7 @@ impl ExecutionStrategy for CrossThread2 {
         let server_thread = thread::current();
         let state2 = state.clone();
         let join_handle = thread::spawn(move || {
-            let mut dispatch = |b| {
+            let r = with_client_thread_dispatch(&mut |b| {
                 *state2.lock().unwrap() = State::Req(b);
                 server_thread.unpark();
                 loop {
@@ -240,17 +214,7 @@ impl ExecutionStrategy for CrossThread2 {
                         break b.take();
                     }
                 }
-            };
-
-            let r = run_client(
-                Bridge {
-                    cached_buffer: input,
-                    dispatch: (&mut dispatch).into(),
-                    force_show_panics,
-                    _marker: marker::PhantomData,
-                },
-                client_data,
-            );
+            });
 
             // Wake up the server so it can exit the dispatch loop.
             drop(state2);
@@ -266,7 +230,7 @@ impl ExecutionStrategy for CrossThread2 {
                 State::Req(b) => b.take(),
                 _ => continue,
             };
-            b = dispatcher.dispatch(b.take());
+            b = server_thread_dispatch(b.take());
             *state.lock().unwrap() = State::Res(b);
             join_handle.thread().unpark();
         }
@@ -275,6 +239,60 @@ impl ExecutionStrategy for CrossThread2 {
     }
 }
 
+fn run_bridge_and_client<D: Copy + Send + 'static>(
+    strategy: &impl ExecutionStrategy,
+    server_thread_dispatch: impl FnMut(Buffer<u8>) -> Buffer<u8>,
+    input: Buffer<u8>,
+    run_client: extern "C" fn(Bridge, D) -> Buffer<u8>,
+    client_data: D,
+    force_show_panics: bool,
+) -> Buffer<u8> {
+    enum OptionDynDispatchL {}
+
+    impl<'a> scoped_cell::ApplyL<'a> for OptionDynDispatchL {
+        type Out = Option<DynDispatch<'a>>;
+    }
+
+    thread_local! {
+        /// Dispatch callback held in server TLS, and using server ABI, but
+        /// on the client thread (which can differ from the server thread).
+        //
+        // FIXME(eddyb) how redundant is this with the (also) thread-local
+        // client-side `BridgeState`? Some of that indirection can probably
+        // be removed, as long as concerns around further isolation methods
+        // (IPC and/or wasm) are considered.
+        static CLIENT_THREAD_DISPATCH: scoped_cell::ScopedCell<OptionDynDispatchL> =
+            scoped_cell::ScopedCell::new(None);
+    }
+
+    strategy.cross_thread_dispatch(server_thread_dispatch, move |client_thread_dispatch| {
+        CLIENT_THREAD_DISPATCH.with(|dispatch_slot| {
+            dispatch_slot.set(Some(client_thread_dispatch), || {
+                extern "C" fn dispatch(b: Buffer<u8>) -> Buffer<u8> {
+                    CLIENT_THREAD_DISPATCH.with(|dispatch_slot| {
+                        dispatch_slot.replace_during(None, |mut client_thread_dispatch| {
+                            client_thread_dispatch.as_mut().expect(
+                                "proc_macro::bridge::server: dispatch used on \
+                                 thread lacking an active server-side dispatcher",
+                            )(b)
+                        })
+                    })
+                }
+
+                run_client(
+                    Bridge {
+                        cached_buffer: input,
+                        dispatch,
+                        force_show_panics,
+                        _marker: marker::PhantomData,
+                    },
+                    client_data,
+                )
+            })
+        })
+    })
+}
+
 fn run_server<
     S: Server,
     I: Encode<HandleStore<MarkedTypes<S>>>,
@@ -285,7 +303,7 @@ fn run_server<
     handle_counters: &'static client::HandleCounters,
     server: S,
     input: I,
-    run_client: extern "C" fn(Bridge<'_>, D) -> Buffer<u8>,
+    run_client: extern "C" fn(Bridge, D) -> Buffer<u8>,
     client_data: D,
     force_show_panics: bool,
 ) -> Result<O, PanicMessage> {
@@ -295,8 +313,9 @@ fn run_server<
     let mut b = Buffer::new();
     input.encode(&mut b, &mut dispatcher.handle_store);
 
-    b = strategy.run_bridge_and_client(
-        &mut dispatcher,
+    b = run_bridge_and_client(
+        strategy,
+        |b| dispatcher.dispatch(b),
         b,
         run_client,
         client_data,
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 64e25f803b27f..72b7f5f6612d8 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -156,7 +156,7 @@ pub(crate) fn maybe_download_ci_llvm(builder: &Builder<'_>) {
         let llvm_lib = llvm_root.join("lib");
         for entry in t!(fs::read_dir(&llvm_lib)) {
             let lib = t!(entry).path();
-            if lib.ends_with(".so") {
+            if lib.extension().map_or(false, |ext| ext == "so") {
                 fix_bin_or_dylib(builder, &lib);
             }
         }
@@ -284,7 +284,7 @@ fn fix_bin_or_dylib(builder: &Builder<'_>, fname: &Path) {
         entries
     };
     patchelf.args(&[OsString::from("--set-rpath"), rpath_entries]);
-    if !fname.ends_with(".so") {
+    if !fname.extension().map_or(false, |ext| ext == "so") {
         // Finally, set the corret .interp for binaries
         let dynamic_linker_path = nix_deps_dir.join("nix-support/dynamic-linker");
         // FIXME: can we support utf8 here? `args` doesn't accept Vec<u8>, only OsString ...