TODO: make tracking issue

This is maybe gated by some sort of agreement on RFC 3917?

Author: pmur

compiler/rustc_feature/src/unstable.rs

@@ -551,7 +551,7 @@ declare_features! (
     /// Allows associated types in inherent impls.
     (incomplete, inherent_associated_types, "1.52.0", Some(8995)),
     /// Enable #[instrument_fn] on function (todo: tracking issue)
-    (unstable, instrument_fn, "CURRENT_RUSTC_VERSION", None),
+    (unstable, instrument_fn, "CURRENT_RUSTC_VERSION", Some(99999)),
     /// Allows using `pointer` and `reference` in intra-doc links
     (unstable, intra_doc_pointers, "1.51.0", Some(80896)),
     /// lahfsahf target feature on x86.