target_features: control separately whether enabling and disabling a target feature is allowed

Author: RalfJung

src/gcc_util.rs

@@ -96,7 +96,7 @@ pub(crate) fn global_gcc_features(sess: &Session, diagnostics: bool) -> Vec<Stri
                     }
                     Some((_, stability, _)) => {
                         if let Err(reason) =
-                            stability.compute_toggleability(&sess.target).allow_toggle()
+                            stability.toggle_allowed(&sess.target, enable_disable == '+')
                         {
                             sess.dcx().emit_warn(ForbiddenCTargetFeature { feature, reason });
                         } else if stability.requires_nightly().is_some() {

src/lib.rs

@@ -483,9 +483,9 @@ fn target_features_cfg(
         .rust_target_features()
         .iter()
         .filter(|(_, gate, _)| gate.in_cfg())
-        .filter_map(|&(feature, gate, _)| {
+        .filter_map(|(feature, gate, _)| {
             if sess.is_nightly_build() || allow_unstable || gate.requires_nightly().is_none() {
-                Some(feature)
+                Some(*feature)
             } else {
                 None
             }