Rollup of 9 pull requests

compiler/rustc_attr/src/builtin.rs

@@ -135,9 +135,42 @@ impl ConstStability {
 #[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
 #[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, allowed_through_unstable_modules: bool },
+    /// `#[unstable]`
+    Unstable {
+        /// Reason for the current stability level.
+        reason: Option<Symbol>,
+        /// Relevant `rust-lang/rust` issue.
+        issue: Option<NonZeroU32>,
+        is_soft: bool,
+        /// If part of a feature is stabilized and a new feature is added for the remaining parts,
+        /// then the `implied_by` attribute is used to indicate which now-stable feature previously
+        /// contained a item.
+        ///
+        /// ```pseudo-Rust
+        /// #[unstable(feature = "foo", issue = "...")]
+        /// fn foo() {}
+        /// #[unstable(feature = "foo", issue = "...")]
+        /// fn foobar() {}
+        /// ```
+        ///
+        /// ...becomes...
+        ///
+        /// ```pseudo-Rust
+        /// #[stable(feature = "foo", since = "1.XX.X")]
+        /// fn foo() {}
+        /// #[unstable(feature = "foobar", issue = "...", implied_by = "foo")]
+        /// fn foobar() {}
+        /// ```
+        implied_by: Option<Symbol>,
+    },
+    /// `#[stable]`
+    Stable {
+        /// Rust release which stabilized this feature.
+        since: Symbol,
+        /// Is this item allowed to be referred to on stable, despite being contained in unstable
+        /// modules?
+        allowed_through_unstable_modules: bool,
+    },
 }
 
 impl StabilityLevel {
@@ -243,6 +276,7 @@ where
                     let mut issue = None;
                     let mut issue_num = None;
                     let mut is_soft = false;
+                    let mut implied_by = None;
                     for meta in metas {
                         let Some(mi) = meta.meta_item() else {
                             handle_errors(
@@ -308,6 +342,11 @@ where
                                 }
                                 is_soft = true;
                             }
+                            sym::implied_by => {
+                                if !get(mi, &mut implied_by) {
+                                    continue 'outer;
+                                }
+                            }
                             _ => {
                                 handle_errors(
                                     &sess.parse_sess,
@@ -332,7 +371,7 @@ where
                                 );
                                 continue;
                             }
-                            let level = Unstable { reason, issue: issue_num, is_soft };
+                            let level = Unstable { reason, issue: issue_num, is_soft, implied_by };
                             if sym::unstable == meta_name {
                                 stab = Some((Stability { level, feature }, attr.span));
                             } else {
@@ -391,7 +430,7 @@ where
                                         meta.span(),
                                         AttrError::UnknownMetaItem(
                                             pprust::path_to_string(&mi.path),
-                                            &["since", "note"],
+                                            &["feature", "since"],
                                         ),
                                     );
                                     continue 'outer;

compiler/rustc_builtin_macros/src/format.rs

@@ -485,7 +485,7 @@ impl<'a, 'b> Context<'a, 'b> {
             if let Some(span) = fmt.width_span {
                 let span = self.fmtsp.from_inner(InnerSpan::new(span.start, span.end));
                 match fmt.width {
-                    parse::CountIsParam(pos) if pos > self.num_args() => {
+                    parse::CountIsParam(pos) if pos >= self.num_args() => {
                         e.span_label(
                             span,
                             &format!(
@@ -1004,9 +1004,7 @@ fn lint_named_arguments_used_positionally(
                 node_id: ast::CRATE_NODE_ID,
                 lint_id: LintId::of(&NAMED_ARGUMENTS_USED_POSITIONALLY),
                 diagnostic: BuiltinLintDiagnostics::NamedArgumentUsedPositionally(
-                    arg_span,
-                    span,
-                    symbol.to_string(),
+                    arg_span, span, symbol,
                 ),
             });
         }

compiler/rustc_errors/src/diagnostic.rs

@@ -390,18 +390,17 @@ impl Diagnostic {
         expected: DiagnosticStyledString,
         found: DiagnosticStyledString,
     ) -> &mut Self {
-        let mut msg: Vec<_> =
-            vec![("required when trying to coerce from type `".to_string(), Style::NoStyle)];
+        let mut msg: Vec<_> = vec![("required when trying to coerce from type `", Style::NoStyle)];
         msg.extend(expected.0.iter().map(|x| match *x {
-            StringPart::Normal(ref s) => (s.to_owned(), Style::NoStyle),
-            StringPart::Highlighted(ref s) => (s.to_owned(), Style::Highlight),
+            StringPart::Normal(ref s) => (s.as_str(), Style::NoStyle),
+            StringPart::Highlighted(ref s) => (s.as_str(), Style::Highlight),
         }));
-        msg.push(("` to type '".to_string(), Style::NoStyle));
+        msg.push(("` to type '", Style::NoStyle));
         msg.extend(found.0.iter().map(|x| match *x {
-            StringPart::Normal(ref s) => (s.to_owned(), Style::NoStyle),
-            StringPart::Highlighted(ref s) => (s.to_owned(), Style::Highlight),
+            StringPart::Normal(ref s) => (s.as_str(), Style::NoStyle),
+            StringPart::Highlighted(ref s) => (s.as_str(), Style::Highlight),
         }));
-        msg.push(("`".to_string(), Style::NoStyle));
+        msg.push(("`", Style::NoStyle));
 
         // For now, just attach these as notes
         self.highlighted_note(msg);

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -512,7 +512,18 @@ fn out_of_bounds_err<'a>(
     span: Span,
     ty: &str,
 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-    cx.struct_span_err(span, &format!("{ty} depth must be less than {max}"))
+    let msg = if max == 0 {
+        format!(
+            "meta-variable expression `{ty}` with depth parameter \
+             must be called inside of a macro repetition"
+        )
+    } else {
+        format!(
+            "depth parameter on meta-variable expression `{ty}` \
+             must be less than {max}"
+        )
+    };
+    cx.struct_span_err(span, &msg)
 }
 
 fn transcribe_metavar_expr<'a>(

compiler/rustc_lint_defs/src/lib.rs

@@ -467,7 +467,7 @@ pub enum BuiltinLintDiagnostics {
         /// If true, the lifetime will be fully elided.
         use_span: Option<(Span, bool)>,
     },
-    NamedArgumentUsedPositionally(Option<Span>, Span, String),
+    NamedArgumentUsedPositionally(Option<Span>, Span, Symbol),
 }
 
 /// Lints that are buffered up early on in the `Session` before the

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -951,6 +951,13 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         tcx.arena.alloc_from_iter(self.root.lib_features.decode(self))
     }
 
+    /// Iterates over the stability implications in the given crate (when a `#[unstable]` attribute
+    /// has an `implied_by` meta item, then the mapping from the implied feature to the actual
+    /// feature is a stability implication).
+    fn get_stability_implications(self, tcx: TyCtxt<'tcx>) -> &'tcx [(Symbol, Symbol)] {
+        tcx.arena.alloc_from_iter(self.root.stability_implications.decode(self))
+    }
+
     /// Iterates over the language items in the given crate.
     fn get_lang_items(self, tcx: TyCtxt<'tcx>) -> &'tcx [(DefId, usize)] {
         tcx.arena.alloc_from_iter(

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -291,6 +291,9 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         tcx.arena.alloc_slice(&result)
     }
     defined_lib_features => { cdata.get_lib_features(tcx) }
+    stability_implications => {
+        cdata.get_stability_implications(tcx).iter().copied().collect()
+    }
     is_intrinsic => { cdata.get_is_intrinsic(def_id.index) }
     defined_lang_items => { cdata.get_lang_items(tcx) }
     diagnostic_items => { cdata.get_diagnostic_items() }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -538,6 +538,11 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let lib_features = self.encode_lib_features();
         let lib_feature_bytes = self.position() - i;
 
+        // Encode the stability implications.
+        i = self.position();
+        let stability_implications = self.encode_stability_implications();
+        let stability_implications_bytes = self.position() - i;
+
         // Encode the language items.
         i = self.position();
         let lang_items = self.encode_lang_items();
@@ -686,6 +691,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             crate_deps,
             dylib_dependency_formats,
             lib_features,
+            stability_implications,
             lang_items,
             diagnostic_items,
             lang_items_missing,
@@ -710,6 +716,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let computed_total_bytes = preamble_bytes
             + dep_bytes
             + lib_feature_bytes
+            + stability_implications_bytes
             + lang_item_bytes
             + diagnostic_item_bytes
             + native_lib_bytes
@@ -761,6 +768,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             p("preamble", preamble_bytes);
             p("dep", dep_bytes);
             p("lib feature", lib_feature_bytes);
+            p("stability_implications", stability_implications_bytes);
             p("lang item", lang_item_bytes);
             p("diagnostic item", diagnostic_item_bytes);
             p("native lib", native_lib_bytes);
@@ -1777,6 +1785,13 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         self.lazy_array(lib_features.to_vec())
     }
 
+    fn encode_stability_implications(&mut self) -> LazyArray<(Symbol, Symbol)> {
+        empty_proc_macro!(self);
+        let tcx = self.tcx;
+        let implications = tcx.stability_implications(LOCAL_CRATE);
+        self.lazy_array(implications.iter().map(|(k, v)| (*k, *v)))
+    }
+
     fn encode_diagnostic_items(&mut self) -> LazyArray<(Symbol, DefIndex)> {
         empty_proc_macro!(self);
         let tcx = self.tcx;

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -226,6 +226,7 @@ pub(crate) struct CrateRoot {
     crate_deps: LazyArray<CrateDep>,
     dylib_dependency_formats: LazyArray<Option<LinkagePreference>>,
     lib_features: LazyArray<(Symbol, Option<Symbol>)>,
+    stability_implications: LazyArray<(Symbol, Symbol)>,
     lang_items: LazyArray<(DefIndex, usize)>,
     lang_items_missing: LazyArray<lang_items::LangItem>,
     diagnostic_items: LazyArray<(Symbol, DefIndex)>,

compiler/rustc_middle/src/middle/mod.rs

@@ -3,23 +3,23 @@ pub mod dependency_format;
 pub mod exported_symbols;
 pub mod lang_items;
 pub mod lib_features {
-    use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-    use rustc_span::symbol::Symbol;
+    use rustc_data_structures::fx::FxHashMap;
+    use rustc_span::{symbol::Symbol, Span};
 
     #[derive(HashStable, Debug)]
     pub struct LibFeatures {
-        // A map from feature to stabilisation version.
-        pub stable: FxHashMap<Symbol, Symbol>,
-        pub unstable: FxHashSet<Symbol>,
+        /// A map from feature to stabilisation version.
+        pub stable: FxHashMap<Symbol, (Symbol, Span)>,
+        pub unstable: FxHashMap<Symbol, Span>,
     }
 
     impl LibFeatures {
         pub fn to_vec(&self) -> Vec<(Symbol, Option<Symbol>)> {
             let mut all_features: Vec<_> = self
                 .stable
                 .iter()
-                .map(|(f, s)| (*f, Some(*s)))
-                .chain(self.unstable.iter().map(|f| (*f, None)))
+                .map(|(f, (s, _))| (*f, Some(*s)))
+                .chain(self.unstable.iter().map(|(f, _)| (*f, None)))
                 .collect();
             all_features.sort_unstable_by(|a, b| a.0.as_str().partial_cmp(b.0.as_str()).unwrap());
             all_features

compiler/rustc_middle/src/middle/stability.rs

@@ -62,6 +62,19 @@ pub struct Index {
     pub stab_map: FxHashMap<LocalDefId, Stability>,
     pub const_stab_map: FxHashMap<LocalDefId, ConstStability>,
     pub depr_map: FxHashMap<LocalDefId, DeprecationEntry>,
+    /// Mapping from feature name to feature name based on the `implied_by` field of `#[unstable]`
+    /// attributes. If a `#[unstable(feature = "implier", implied_by = "impliee")]` attribute
+    /// exists, then this map will have a `impliee -> implier` entry.
+    ///
+    /// This mapping is necessary unless both the `#[stable]` and `#[unstable]` attributes should
+    /// specify their implications (both `implies` and `implied_by`). If only one of the two
+    /// attributes do (as in the current implementation, `implied_by` in `#[unstable]`), then this
+    /// mapping is necessary for diagnostics. When a "unnecessary feature attribute" error is
+    /// reported, only the `#[stable]` attribute information is available, so the map is necessary
+    /// to know that the feature implies another feature. If it were reversed, and the `#[stable]`
+    /// attribute had an `implies` meta item, then a map would be necessary when avoiding a "use of
+    /// unstable feature" error for a feature that was implied.
+    pub implications: FxHashMap<Symbol, Symbol>,
 }
 
 impl Index {
@@ -423,7 +436,9 @@ impl<'tcx> TyCtxt<'tcx> {
 
         match stability {
             Some(Stability {
-                level: attr::Unstable { reason, issue, is_soft }, feature, ..
+                level: attr::Unstable { reason, issue, is_soft, implied_by },
+                feature,
+                ..
             }) => {
                 if span.allows_unstable(feature) {
                     debug!("stability: skipping span={:?} since it is internal", span);
@@ -433,6 +448,13 @@ impl<'tcx> TyCtxt<'tcx> {
                     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) {
+                    return EvalResult::Allow;
+                }
+
                 // When we're compiling the compiler itself we may pull in
                 // crates from crates.io, but those crates may depend on other
                 // crates also pulled in from crates.io. We want to ideally be

compiler/rustc_middle/src/query/mod.rs

@@ -1634,11 +1634,15 @@ rustc_queries! {
         storage(ArenaCacheSelector<'tcx>)
         desc { "calculating the lib features map" }
     }
-    query defined_lib_features(_: CrateNum)
-        -> &'tcx [(Symbol, Option<Symbol>)] {
+    query defined_lib_features(_: CrateNum) -> &'tcx [(Symbol, Option<Symbol>)] {
         desc { "calculating the lib features defined in a crate" }
         separate_provide_extern
     }
+    query stability_implications(_: CrateNum) -> FxHashMap<Symbol, Symbol> {
+        storage(ArenaCacheSelector<'tcx>)
+        desc { "calculating the implications between `#[unstable]` features defined in a crate" }
+        separate_provide_extern
+    }
     /// Whether the function is an intrinsic
     query is_intrinsic(def_id: DefId) -> bool {
         desc { |tcx| "is_intrinsic({})", tcx.def_path_str(def_id) }

compiler/rustc_parse_format/src/lib.rs

@@ -572,9 +572,10 @@ impl<'a> Parser<'a> {
             // '0' flag and then an ill-formatted format string with just a '$'
             // and no count, but this is better if we instead interpret this as
             // no '0' flag and '0$' as the width instead.
-            if self.consume('$') {
+            if let Some(end) = self.consume_pos('$') {
                 spec.width = CountIsParam(0);
                 havewidth = true;
+                spec.width_span = Some(self.to_span_index(end - 1).to(self.to_span_index(end + 1)));
             } else {
                 spec.flags |= 1 << (FlagSignAwareZeroPad as u32);
             }

compiler/rustc_parse_format/src/tests.rs

@@ -178,6 +178,23 @@ fn format_counts() {
             },
         })],
     );
+    same(
+        "{1:0$.10x}",
+        &[NextArgument(Argument {
+            position: ArgumentIs(1),
+            format: FormatSpec {
+                fill: None,
+                align: AlignUnknown,
+                flags: 0,
+                precision: CountIs(10),
+                width: CountIsParam(0),
+                precision_span: None,
+                width_span: Some(InnerSpan::new(4, 6)),
+                ty: "x",
+                ty_span: None,
+            },
+        })],
+    );
     same(
         "{:.*x}",
         &[NextArgument(Argument {