Replace Index impl with enabled method

Author: ecstatic-morse

src/librustc_feature/active.rs

@@ -52,14 +52,10 @@ macro_rules! declare_features {
             pub fn walk_feature_fields(&self, mut f: impl FnMut(&str, bool)) {
                 $(f(stringify!($feature), self.$feature);)+
             }
-        }
-
-        impl std::ops::Index<Symbol> for Features {
-            type Output = bool;
 
-            fn index(&self, feature: Symbol) -> &Self::Output {
+            pub fn enabled(&self, feature: Symbol) -> bool {
                 match feature {
-                    $( sym::$feature => &self.$feature, )*
+                    $( sym::$feature => self.$feature, )*
 
                     _ => panic!("`{}` was not listed in `declare_features`", feature),
                 }

src/librustc_passes/check_const.rs

@@ -137,7 +137,7 @@ impl<'tcx> CheckConstVisitor<'tcx> {
         let gates = expr.required_feature_gates();
         match gates {
             // Don't emit an error if the user has enabled the requisite feature gates.
-            Some(gates) if gates.iter().all(|&g| features[g]) => return,
+            Some(gates) if gates.iter().all(|&g| features.enabled(g)) => return,
 
             // `-Zunleash-the-miri-inside-of-you` only works for expressions that don't have a
             // corresponding feature gate. This encourages nightly users to use feature gates when
@@ -158,7 +158,7 @@ impl<'tcx> CheckConstVisitor<'tcx> {
         let missing_gates: Vec<_> = gates
             .iter()
             .copied()
-            .filter(|&g| !features[g])
+            .filter(|&g| !features.enabled(g))
             .collect();
 
         match missing_gates.as_slice() {