Coerce const FnDefs to implement const Fn traits

compiler/rustc_middle/src/ty/context.rs

@@ -2750,7 +2750,10 @@ impl<'tcx> TyCtxt<'tcx> {
                 Some(stability) if stability.level.is_unstable() => {
                     // has a `rustc_const_unstable` attribute, check whether the user enabled the
                     // corresponding feature gate.
-                    self.features().declared_lib_features.iter().any(|&(sym, _)| sym == stability.feature)
+                    self.features()
+                        .declared_lib_features
+                        .iter()
+                        .any(|&(sym, _)| sym == stability.feature)
                 }
                 // functions without const stability are either stable user written
                 // const fn or the user is using feature gates and we thus don't