Rename `Features::active_features`.

The word "active" is currently used in two different and confusing ways:
- `ACTIVE_FEATURES` actually means "available unstable features"
- `Features::active_features` actually means "features declared in the
  crate's code", which can include feature within `ACTIVE_FEATURES` but
  also others.

(This is also distinct from "enabled" features which includes declared
features but also some edition-specific features automatically enabled
depending on the edition in use.)

This commit changes the `Features::active_features` to
`Features::declared_features` which actually matches its meaning.
Likewise, `Features::active` becomes `Features::declared`.

compiler/rustc_expand/src/config.rs

@@ -155,7 +155,7 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute]) -> Features {
             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
                 let since = Some(Symbol::intern(since));
                 features.declared_lang_features.push((name, mi.span(), since));
-                features.active_features.insert(name);
+                features.declared_features.insert(name);
                 continue;
             }
 
@@ -173,14 +173,14 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute]) -> Features {
             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
                 f.set(&mut features);
                 features.declared_lang_features.push((name, mi.span(), None));
-                features.active_features.insert(name);
+                features.declared_features.insert(name);
                 continue;
             }
 
             // Otherwise, the feature is unknown. Record it at a lib feature.
             // It will be checked later.
             features.declared_lib_features.push((name, mi.span()));
-            features.active_features.insert(name);
+            features.declared_features.insert(name);
         }
     }
 

compiler/rustc_feature/src/active.rs

@@ -60,8 +60,9 @@ macro_rules! declare_features {
             pub declared_lang_features: Vec<(Symbol, Span, Option<Symbol>)>,
             /// `#![feature]` attrs for non-language (library) features.
             pub declared_lib_features: Vec<(Symbol, Span)>,
-            /// Features enabled for this crate.
-            pub active_features: FxHashSet<Symbol>,
+            /// `declared_lang_features` + `declared_lib_features`.
+            pub declared_features: FxHashSet<Symbol>,
+            /// Individual features (unstable only).
             $(
                 $(#[doc = $doc])*
                 pub $feature: bool
@@ -73,12 +74,14 @@ macro_rules! declare_features {
                 $(f(stringify!($feature), self.$feature);)+
             }
 
-            /// Is the given feature active?
-            pub fn active(&self, feature: Symbol) -> bool {
-                self.active_features.contains(&feature)
+            /// Is the given feature explicitly declared, i.e. named in a
+            /// `#![feature(...)]` within the code?
+            pub fn declared(&self, feature: Symbol) -> bool {
+                self.declared_features.contains(&feature)
             }
 
-            /// Is the given feature enabled?
+            /// Is the given feature enabled, i.e. declared or automatically
+            /// enabled due to the edition?
             ///
             /// Panics if the symbol doesn't correspond to a declared feature.
             pub fn enabled(&self, feature: Symbol) -> bool {

compiler/rustc_middle/src/middle/stability.rs

@@ -448,14 +448,14 @@ impl<'tcx> TyCtxt<'tcx> {
                     debug!("stability: skipping span={:?} since it is internal", span);
                     return EvalResult::Allow;
                 }
-                if self.features().active(feature) {
+                if self.features().declared(feature) {
                     return EvalResult::Allow;
                 }
 
                 // If this item was previously part of a now-stabilized feature which is still
                 // active (i.e. the user hasn't removed the attribute for the stabilized feature
                 // yet) then allow use of this item.
-                if let Some(implied_by) = implied_by && self.features().active(implied_by) {
+                if let Some(implied_by) = implied_by && self.features().declared(implied_by) {
                     return EvalResult::Allow;
                 }
 
@@ -532,7 +532,7 @@ impl<'tcx> TyCtxt<'tcx> {
                     debug!("body stability: skipping span={:?} since it is internal", span);
                     return EvalResult::Allow;
                 }
-                if self.features().active(feature) {
+                if self.features().declared(feature) {
                     return EvalResult::Allow;
                 }
 

src/tools/clippy/clippy_lints/src/manual_float_methods.rs

@@ -85,7 +85,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualFloatMethods {
         if !in_external_macro(cx.sess(), expr.span)
             && (
                 matches!(cx.tcx.constness(cx.tcx.hir().enclosing_body_owner(expr.hir_id)), Constness::NotConst)
-                    || cx.tcx.features().active(sym!(const_float_classify))
+                    || cx.tcx.features().declared(sym!(const_float_classify))
             ) && let ExprKind::Binary(kind, lhs, rhs) = expr.kind
             && let ExprKind::Binary(lhs_kind, lhs_lhs, lhs_rhs) = lhs.kind
             && let ExprKind::Binary(rhs_kind, rhs_lhs, rhs_rhs) = rhs.kind