1 files changed, 30 insertions, 0 deletions

diff --git a/crates/proc_macro_srv/src/proc_macro/bridge/closure.rs b/crates/proc_macro_srv/src/proc_macro/bridge/closure.rs
new file mode 100644
index 000000000..273a97715
--- /dev/null
+++ b/crates/proc_macro_srv/src/proc_macro/bridge/closure.rs
@@ -0,0 +1,30 @@
+//! lib-proc-macro Closure type (equivalent to `&mut dyn FnMut(A) -> R`) that's `repr(C)`.
+//!
+//! Copy from https://github.com/rust-lang/rust/blob/6050e523bae6de61de4e060facc43dc512adaccd/src/libproc_macro/bridge/closure.rs#
+//! augmented with removing unstable features
+
+#[repr(C)]
+pub struct Closure<'a, A, R> {
+    call: unsafe extern "C" fn(&mut Env, A) -> R,
+    env: &'a mut Env,
+}
+
+struct Env;
+
+// impl<'a, A, R> !Sync for Closure<'a, A, R> {}
+// impl<'a, A, R> !Send for Closure<'a, A, R> {}
+
+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: unsafe { &mut *(f as *mut _ as *mut Env) } }
+    }
+}
+
+impl<'a, A, R> Closure<'a, A, R> {
+    pub fn call(&mut self, arg: A) -> R {
+        unsafe { (self.call)(self.env, arg) }
+    }
+}