update catch_unwind doc comments to indicate that catching a foreign exception is UB

Author: BatmanAoD

library/core/src/intrinsics.rs

@@ -2392,7 +2392,9 @@ extern "rust-intrinsic" {
     pub fn variant_count<T>() -> usize;
 
     /// Rust's "try catch" construct for unwinding. Invokes the function pointer `try_fn` with the
-    /// data pointer `data`, and calls `catch_fn` if unwinding occurs while `try_fn` runs.
+    /// data pointer `data`, and calls `catch_fn` if a panic occurs while `try_fn` runs. (It is
+    /// undefined behavior to catch an unwinding operation from another language with this
+    /// function.)
     ///
     /// `catch_fn` must not unwind.
     ///

library/std/src/panic.rs

@@ -316,16 +316,18 @@ where
 ///
 /// # Notes
 ///
-/// Note that this function **might not catch all panics** in Rust. A panic in
-/// Rust is not always implemented via unwinding, but can be implemented by
-/// aborting the process as well. This function *only* catches unwinding panics,
-/// not those that abort the process.
-///
-/// Note that if a custom panic hook has been set, it will be invoked before
-/// the panic is caught, before unwinding.
-///
-/// Also note that unwinding into Rust code with a foreign exception (e.g.
-/// an exception thrown from C++ code) is undefined behavior.
+/// This function **might not catch all panics** in Rust. A panic in Rust is not
+/// always implemented via unwinding, but can be implemented by aborting the
+/// process as well. This function *only* catches unwinding panics, not those
+/// that abort the process.
+///
+/// If a custom panic hook has been set, it will be invoked before the panic is
+/// caught, before unwinding.
+///
+/// Although unwinding into Rust code with a foreign exception (e.g. an
+/// exception thrown from C++ code) via an appropriate ABI (e.g. `"C-unwind"`)
+/// is permitted, catching such an exception using this function is undefined
+/// behavior.
 ///
 /// Finally, be **careful in how you drop the result of this function**.
 /// If it is `Err`, it contains the panic payload, and dropping that may in turn panic!