Add and use stability helper methods

This avoids an ambiguity (when reading) where `.level.is_stable()` is
not immediately clear whether it is general stability or const
stability.

compiler/rustc_attr/src/builtin.rs

@@ -101,6 +101,16 @@ pub struct Stability {
     pub feature: Symbol,
 }
 
+impl Stability {
+    pub fn is_unstable(&self) -> bool {
+        self.level.is_unstable()
+    }
+
+    pub fn is_stable(&self) -> bool {
+        self.level.is_stable()
+    }
+}
+
 /// Represents the `#[rustc_const_unstable]` and `#[rustc_const_stable]` attributes.
 #[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
 #[derive(HashStable_Generic)]
@@ -111,6 +121,16 @@ pub struct ConstStability {
     pub promotable: bool,
 }
 
+impl ConstStability {
+    pub fn is_const_unstable(&self) -> bool {
+        self.level.is_unstable()
+    }
+
+    pub fn is_const_stable(&self) -> bool {
+        self.level.is_stable()
+    }
+}
+
 /// The available stability levels.
 #[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
 #[derive(HashStable_Generic)]

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -9,7 +9,7 @@ use rustc_span::symbol::Symbol;
 pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
     if tcx.is_const_fn_raw(def_id) {
         let const_stab = tcx.lookup_const_stability(def_id)?;
-        if const_stab.level.is_unstable() { Some(const_stab.feature) } else { None }
+        if const_stab.is_const_unstable() { Some(const_stab.feature) } else { None }
     } else {
         None
     }

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -944,7 +944,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 // have no `rustc_const_stable` attributes to be const-unstable as well. This
                 // should be fixed later.
                 let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none()
-                    && tcx.lookup_stability(callee).map_or(false, |s| s.level.is_unstable());
+                    && tcx.lookup_stability(callee).map_or(false, |s| s.is_unstable());
                 if callee_is_unstable_unmarked {
                     trace!("callee_is_unstable_unmarked");
                     // We do not use `const` modifiers for intrinsic "functions", as intrinsics are

compiler/rustc_middle/src/ty/context.rs

@@ -2791,7 +2791,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn is_const_fn(self, def_id: DefId) -> bool {
         if self.is_const_fn_raw(def_id) {
             match self.lookup_const_stability(def_id) {
-                Some(stability) if stability.level.is_unstable() => {
+                Some(stability) if stability.is_const_unstable() => {
                     // has a `rustc_const_unstable` attribute, check whether the user enabled the
                     // corresponding feature gate.
                     self.features()

compiler/rustc_passes/src/stability.rs

@@ -147,7 +147,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             // Propagate unstability.  This can happen even for non-staged-api crates in case
             // -Zforce-unstable-if-unmarked is set.
             if let Some(stab) = self.parent_stab {
-                if inherit_deprecation.yes() && stab.level.is_unstable() {
+                if inherit_deprecation.yes() && stab.is_unstable() {
                     self.index.stab_map.insert(def_id, stab);
                 }
             }
@@ -190,7 +190,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
         if const_stab.is_none() {
             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
             if let Some(parent) = self.parent_const_stab {
-                if parent.level.is_unstable() {
+                if parent.is_const_unstable() {
                     self.index.const_stab_map.insert(def_id, parent);
                 }
             }
@@ -272,9 +272,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
         if stab.is_none() {
             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
             if let Some(stab) = self.parent_stab {
-                if inherit_deprecation.yes() && stab.level.is_unstable()
+                if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
-                    || inherit_from_parent.yes()
-                {
                     self.index.stab_map.insert(def_id, stab);
                 }
             }

src/librustdoc/clean/inline.rs

@@ -344,7 +344,7 @@ crate fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if stab.is_unstable() && stab.feature == sym::rustc_private {
                     return;
                 }
             }
@@ -373,7 +373,7 @@ crate fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if stab.is_unstable() && stab.feature == sym::rustc_private {
                     return;
                 }
             }

src/librustdoc/clean/types.rs

@@ -632,7 +632,7 @@ impl Item {
         self.stability(tcx).as_ref().and_then(|s| {
             let mut classes = Vec::with_capacity(2);
 
-            if s.level.is_unstable() {
+            if s.is_unstable() {
                 classes.push("unstable");
             }
 

src/librustdoc/html/render/print_item.rs

@@ -445,10 +445,7 @@ fn extra_info_tags(item: &clean::Item, parent: &clean::Item, tcx: TyCtxt<'_>) ->
 
     // The "rustc_private" crates are permanently unstable so it makes no sense
     // to render "unstable" everywhere.
-    if item
+    if item.stability(tcx).as_ref().map(|s| s.is_unstable() && s.feature != sym::rustc_private)
-        .stability(tcx)
-        .as_ref()
-        .map(|s| s.level.is_unstable() && s.feature != sym::rustc_private)
         == Some(true)
     {
         tags += &tag_html("unstable", "", "Experimental");