Make feature key optional for rustc_stable, rustc_const_stable attrib…

…utes

… so partial stabilizations no longer have to make up a feature name
that never existed as unstable for the stabilized subset of the API.

compiler/rustc_attr/src/builtin.rs

@@ -95,15 +95,13 @@ pub enum OptimizeAttr {
 #[derive(HashStable_Generic)]
 pub struct Stability {
     pub level: StabilityLevel,
-    pub feature: Symbol,
 }
 
 /// Represents the `#[rustc_const_unstable]` and `#[rustc_const_stable]` attributes.
 #[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
 #[derive(HashStable_Generic)]
 pub struct ConstStability {
     pub level: StabilityLevel,
-    pub feature: Symbol,
     /// whether the function has a `#[rustc_promotable]` attribute
     pub promotable: bool,
 }
@@ -113,8 +111,18 @@ pub struct ConstStability {
 #[derive(HashStable_Generic)]
 pub enum StabilityLevel {
     // Reason for the current stability level and the relevant rust-lang issue
-    Unstable { reason: Option<Symbol>, issue: Option<NonZeroU32>, is_soft: bool },
-    Stable { since: Symbol },
+    Unstable {
+        reason: Option<Symbol>,
+        feature: Symbol,
+        issue: Option<NonZeroU32>,
+        is_soft: bool,
+    },
+    Stable {
+        since: Symbol,
+        // feature flag, should not be set when the feature name remains in use
+        // for unstable items (i.e. when partially stabilizing a feature)
+        feature: Option<Symbol>,
+    },
 }
 
 impl StabilityLevel {
@@ -309,14 +317,12 @@ where
                                 );
                                 continue;
                             }
-                            let level = Unstable { reason, issue: issue_num, is_soft };
+                            let level = Unstable { reason, feature, issue: issue_num, is_soft };
                             if sym::unstable == meta_name {
-                                stab = Some((Stability { level, feature }, attr.span));
+                                stab = Some((Stability { level }, attr.span));
                             } else {
-                                const_stab = Some((
-                                    ConstStability { level, feature, promotable: false },
-                                    attr.span,
-                                ));
+                                const_stab =
+                                    Some((ConstStability { level, promotable: false }, attr.span));
                             }
                         }
                         (None, _, _) => {
@@ -385,22 +391,16 @@ where
                         }
                     }
 
-                    match (feature, since) {
-                        (Some(feature), Some(since)) => {
-                            let level = Stable { since };
+                    match since {
+                        Some(since) => {
+                            let level = Stable { since, feature };
                             if sym::stable == meta_name {
-                                stab = Some((Stability { level, feature }, attr.span));
+                                stab = Some((Stability { level }, attr.span));
                             } else {
-                                const_stab = Some((
-                                    ConstStability { level, feature, promotable: false },
-                                    attr.span,
-                                ));
+                                const_stab =
+                                    Some((ConstStability { level, promotable: false }, attr.span));
                             }
                         }
-                        (None, _) => {
-                            handle_errors(&sess.parse_sess, attr.span, AttrError::MissingFeature);
-                            continue;
-                        }
                         _ => {
                             handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
                             continue;

compiler/rustc_middle/src/middle/stability.rs

@@ -347,7 +347,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
         match stability {
             Some(&Stability {
-                level: attr::Unstable { reason, issue, is_soft }, feature, ..
+                level: attr::Unstable { reason, feature, issue, is_soft }, ..
             }) => {
                 if span.allows_unstable(feature) {
                     debug!("stability: skipping span={:?} since it is internal", span);

compiler/rustc_mir/src/const_eval/fn_queries.rs

@@ -1,3 +1,4 @@
+use rustc_attr::StabilityLevel;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::hir::map::blocks::FnLikeNode;
@@ -27,7 +28,11 @@ pub fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 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 let StabilityLevel::Unstable { feature, .. } = const_stab.level {
+            Some(feature)
+        } else {
+            None
+        }
     } else {
         None
     }

compiler/rustc_passes/src/stability.rs

@@ -231,7 +231,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
 
             // Check if deprecated_since < stable_since. If it is,
             // this is *almost surely* an accident.
-            if let (&Some(dep_since), &attr::Stable { since: stab_since }) =
+            if let (&Some(dep_since), &attr::Stable { since: stab_since, .. }) =
                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
             {
                 // Explicit version of iter::order::lt to handle parse errors properly
@@ -701,10 +701,10 @@ fn stability_index(tcx: TyCtxt<'tcx>, (): ()) -> Index<'tcx> {
             let stability = tcx.intern_stability(Stability {
                 level: attr::StabilityLevel::Unstable {
                     reason: Some(Symbol::intern(reason)),
+                    feature: sym::rustc_private,
                     issue: NonZeroU32::new(27812),
                     is_soft: false,
                 },
-                feature: sym::rustc_private,
             });
             annotator.parent_stab = Some(stability);
         }

compiler/rustc_resolve/src/macros.rs

@@ -1141,8 +1141,7 @@ impl<'a> Resolver<'a> {
     ) {
         let span = path.span;
         if let Some(stability) = &ext.stability {
-            if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
-                let feature = stability.feature;
+            if let StabilityLevel::Unstable { reason, feature, issue, is_soft } = stability.level {
                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
                     let lint_buffer = &mut self.lint_buffer;
                     let soft_handler =

src/librustdoc/clean/inline.rs

@@ -4,6 +4,7 @@ use std::iter::once;
 use std::sync::Arc;
 
 use rustc_ast as ast;
+use rustc_attr::StabilityLevel;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -356,7 +357,7 @@ crate fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if let StabilityLevel::Unstable { feature: sym::rustc_private, .. } = &stab.level {
                     return;
                 }
             }
@@ -388,7 +389,7 @@ crate fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if let StabilityLevel::Unstable { feature: sym::rustc_private, .. } = &stab.level {
                     return;
                 }
             }

src/librustdoc/html/render/mod.rs

@@ -640,11 +640,13 @@ fn short_item_info(
 
     // Render unstable items. But don't render "rustc_private" crates (internal compiler crates).
     // Those crates are permanently unstable so it makes no sense to render "unstable" everywhere.
-    if let Some((StabilityLevel::Unstable { reason, issue, .. }, feature)) = item
+    if let Some(StabilityLevel::Unstable { reason, feature, issue, .. }) = item
         .stability(cx.tcx())
         .as_ref()
-        .filter(|stab| stab.feature != sym::rustc_private)
-        .map(|stab| (stab.level, stab.feature))
+        .filter(|stab| {
+            !matches!(stab.level, StabilityLevel::Unstable { feature: sym::rustc_private, .. })
+        })
+        .map(|stab| stab.level)
     {
         let mut message =
             "<span class=\"emoji\">🔬</span> This is a nightly-only experimental API.".to_owned();
@@ -801,7 +803,7 @@ fn render_stability_since_raw(
 
     match (ver, const_stability) {
         // stable and const stable
-        (Some(v), Some(ConstStability { level: StabilityLevel::Stable { since }, .. }))
+        (Some(v), Some(ConstStability { level: StabilityLevel::Stable { since, .. }, .. }))
             if Some(since.as_str()).as_deref() != containing_const_ver =>
         {
             write!(
@@ -813,7 +815,7 @@ fn render_stability_since_raw(
         // stable and const unstable
         (
             Some(v),
-            Some(ConstStability { level: StabilityLevel::Unstable { issue, .. }, feature, .. }),
+            Some(ConstStability { level: StabilityLevel::Unstable { issue, feature, .. }, .. }),
         ) => {
             write!(
                 w,

src/librustdoc/html/render/print_item.rs

@@ -3,6 +3,7 @@ use clean::AttributesExt;
 use std::cmp::Ordering;
 use std::fmt;
 
+use rustc_attr::StabilityLevel;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_hir::def::CtorKind;
@@ -414,11 +415,10 @@ 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
-        .stability(tcx)
-        .as_ref()
-        .map(|s| s.level.is_unstable() && s.feature != sym::rustc_private)
-        == Some(true)
+    if item.stability(tcx).as_ref().map(|s| {
+        matches!(s.level, StabilityLevel::Unstable { feature, .. } if feature != sym::rustc_private)
+    })
+    == Some(true)
     {
         tags += &tag_html("unstable", "", "Experimental");
     }

src/librustdoc/lib.rs

@@ -12,6 +12,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(never_type)]
 #![feature(once_cell)]
+#![feature(option_result_contains)]
 #![feature(type_ascription)]
 #![recursion_limit = "256"]
 #![warn(rustc::internal)]

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

@@ -368,7 +368,7 @@ fn check_terminator(
 fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId, msrv: Option<&RustcVersion>) -> bool {
     rustc_mir::const_eval::is_const_fn(tcx, def_id)
         && tcx.lookup_const_stability(def_id).map_or(true, |const_stab| {
-            if let rustc_attr::StabilityLevel::Stable { since } = const_stab.level {
+            if let rustc_attr::StabilityLevel::Stable { since, .. } = const_stab.level {
                 // Checking MSRV is manually necessary because `rustc` has no such concept. This entire
                 // function could be removed if `rustc` provided a MSRV-aware version of `is_const_fn`.
                 // as a part of an unimplemented MSRV check https://github.com/rust-lang/rust/issues/65262.