Rollup of 6 pull requests

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -597,7 +597,21 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
             }
         }
-        if !suggestions.is_empty() {
+        suggestions.sort_by_key(|&(span, _)| span);
+        // There are cases where one bound points to a span within another bound's span, like when
+        // you have code like the following (#115019), so we skip providing a suggestion in those
+        // cases to avoid having a malformed suggestion.
+        //
+        // pub struct Flatten<I> {
+        //     inner: <IntoIterator<Item: IntoIterator<Item: >>::IntoIterator as Item>::core,
+        //             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+        //             |                  ^^^^^^^^^^^^^^^^^^^^^
+        //             |                  |
+        //             |                  associated types `Item`, `IntoIter` must be specified
+        //             associated types `Item`, `IntoIter` must be specified
+        // }
+        let overlaps = suggestions.windows(2).any(|pair| pair[0].0.overlaps(pair[1].0));
+        if !suggestions.is_empty() && !overlaps {
             err.multipart_suggestion(
                 format!("specify the associated type{}", pluralize!(types_count)),
                 suggestions,

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -289,6 +289,7 @@ fn default_body_is_unstable(
         &tcx.sess.parse_sess,
         feature,
         rustc_feature::GateIssue::Library(issue),
+        false,
     );
 
     err.emit();

compiler/rustc_index/src/lib.rs

@@ -29,6 +29,18 @@ pub use {idx::Idx, slice::IndexSlice, vec::IndexVec};
 pub use rustc_macros::newtype_index;
 
 /// Type size assertion. The first argument is a type and the second argument is its expected size.
+///
+/// <div class="warning">
+///
+/// Emitting hard errors from size assertions like this is generally not
+/// recommended, especially in libraries, because they can cause build failures if the layout
+/// algorithm or dependencies change. Here in rustc we control the toolchain and layout algorithm,
+/// so the former is not a problem. For the latter we have a lockfile as rustc is an application and
+/// precompiled library.
+///
+/// Short version: Don't copy this macro into your own code. Use a `#[test]` instead.
+///
+/// </div>
 #[macro_export]
 macro_rules! static_assert_size {
     ($ty:ty, $size:expr) => {

compiler/rustc_lint/src/context.rs

@@ -966,6 +966,14 @@ pub trait LintContext: Sized {
                         Applicability::MachineApplicable
                     );
                 }
+                BuiltinLintDiagnostics::AssociatedConstElidedLifetime { elided, span } => {
+                    db.span_suggestion_verbose(
+                        if elided { span.shrink_to_hi() } else { span },
+                        "use the `'static` lifetime",
+                        if elided { "'static " } else { "'static" },
+                        Applicability::MachineApplicable
+                    );
+                }
             }
             // Rewrap `db`, and pass control to the user.
             decorate(db)

compiler/rustc_lint/src/levels.rs

@@ -12,7 +12,7 @@ use rustc_ast as ast;
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{DecorateLint, DiagnosticBuilder, DiagnosticMessage, MultiSpan};
-use rustc_feature::Features;
+use rustc_feature::{Features, GateIssue};
 use rustc_hir as hir;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::HirId;
@@ -24,12 +24,14 @@ use rustc_middle::lint::{
 };
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{RegisteredTools, TyCtxt};
-use rustc_session::lint::builtin::{RENAMED_AND_REMOVED_LINTS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES};
 use rustc_session::lint::{
-    builtin::{self, FORBIDDEN_LINT_GROUPS, SINGLE_USE_LIFETIMES, UNFULFILLED_LINT_EXPECTATIONS},
+    builtin::{
+        self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
+        UNFULFILLED_LINT_EXPECTATIONS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES,
+    },
     Level, Lint, LintExpectationId, LintId,
 };
-use rustc_session::parse::{add_feature_diagnostics, feature_err};
+use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -566,7 +568,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                     continue;
                 }
 
-                if self.check_gated_lint(id, DUMMY_SP) {
+                if self.check_gated_lint(id, DUMMY_SP, true) {
                     let src = LintLevelSource::CommandLine(lint_flag_val, orig_level);
                     self.insert(id, (level, src));
                 }
@@ -837,7 +839,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                             reason,
                         };
                         for &id in *ids {
-                            if self.check_gated_lint(id, attr.span) {
+                            if self.check_gated_lint(id, attr.span, false) {
                                 self.insert_spec(id, (level, src));
                             }
                         }
@@ -854,7 +856,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                                     reason,
                                 };
                                 for &id in ids {
-                                    if self.check_gated_lint(id, attr.span) {
+                                    if self.check_gated_lint(id, attr.span, false) {
                                         self.insert_spec(id, (level, src));
                                     }
                                 }
@@ -955,7 +957,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                             reason,
                         };
                         for &id in ids {
-                            if self.check_gated_lint(id, attr.span) {
+                            if self.check_gated_lint(id, attr.span, false) {
                                 self.insert_spec(id, (level, src));
                             }
                         }
@@ -1000,7 +1002,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
     // FIXME only emit this once for each attribute, instead of repeating it 4 times for
     // pre-expansion lints, post-expansion lints, `shallow_lint_levels_on` and `lint_expectations`.
     #[track_caller]
-    fn check_gated_lint(&self, lint_id: LintId, span: Span) -> bool {
+    fn check_gated_lint(&self, lint_id: LintId, span: Span, lint_from_cli: bool) -> bool {
         if let Some(feature) = lint_id.lint.feature_gate {
             if !self.features.enabled(feature) {
                 let lint = builtin::UNKNOWN_LINTS;
@@ -1015,7 +1017,13 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                     |lint| {
                         lint.set_arg("name", lint_id.lint.name_lower());
                         lint.note(fluent::lint_note);
-                        add_feature_diagnostics(lint, &self.sess.parse_sess, feature);
+                        rustc_session::parse::add_feature_diagnostics_for_issue(
+                            lint,
+                            &self.sess.parse_sess,
+                            feature,
+                            GateIssue::Language,
+                            lint_from_cli,
+                        );
                         lint
                     },
                 );

compiler/rustc_lint_defs/src/builtin.rs

@@ -3376,6 +3376,7 @@ declare_lint_pass! {
         DEPRECATED_IN_FUTURE,
         DEPRECATED_WHERE_CLAUSE_LOCATION,
         DUPLICATE_MACRO_ATTRIBUTES,
+        ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
         ELIDED_LIFETIMES_IN_PATHS,
         EXPORTED_PRIVATE_DEPENDENCIES,
         FFI_UNWIND_CALLS,
@@ -4527,3 +4528,44 @@ declare_lint! {
         reference: "issue #114095 <https://github.com/rust-lang/rust/issues/114095>",
     };
 }
+
+declare_lint! {
+    /// The `elided_lifetimes_in_associated_constant` lint detects elided lifetimes
+    /// that were erroneously allowed in associated constants.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(elided_lifetimes_in_associated_constant)]
+    ///
+    /// struct Foo;
+    ///
+    /// impl Foo {
+    ///     const STR: &str = "hello, world";
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Previous version of Rust
+    ///
+    /// Implicit static-in-const behavior was decided [against] for associated
+    /// constants because of ambiguity. This, however, regressed and the compiler
+    /// erroneously treats elided lifetimes in associated constants as lifetime
+    /// parameters on the impl.
+    ///
+    /// This is a [future-incompatible] lint to transition this to a
+    /// hard error in the future.
+    ///
+    /// [against]: https://github.com/rust-lang/rust/issues/38831
+    /// [future-incompatible]: ../index.md#future-incompatible-lints
+    pub ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
+    Warn,
+    "elided lifetimes cannot be used in associated constants in impls",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseError,
+        reference: "issue #115010 <https://github.com/rust-lang/rust/issues/115010>",
+    };
+}

compiler/rustc_lint_defs/src/lib.rs

@@ -572,6 +572,10 @@ pub enum BuiltinLintDiagnostics {
         /// The span of the unnecessarily-qualified path to remove.
         removal_span: Span,
     },
+    AssociatedConstElidedLifetime {
+        elided: bool,
+        span: Span,
+    },
 }
 
 /// Lints that are buffered up early on in the `Session` before the

compiler/rustc_resolve/src/late.rs

@@ -311,6 +311,10 @@ enum LifetimeRibKind {
     /// error on default object bounds (e.g., `Box<dyn Foo>`).
     AnonymousReportError,
 
+    /// Resolves elided lifetimes to `'static`, but gives a warning that this behavior
+    /// is a bug and will be reverted soon.
+    AnonymousWarnToStatic(NodeId),
+
     /// Signal we cannot find which should be the anonymous lifetime.
     ElisionFailure,
 
@@ -1148,6 +1152,7 @@ impl<'a: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast,
                             }
                             LifetimeRibKind::AnonymousCreateParameter { .. }
                             | LifetimeRibKind::AnonymousReportError
+                            | LifetimeRibKind::AnonymousWarnToStatic(_)
                             | LifetimeRibKind::Elided(_)
                             | LifetimeRibKind::ElisionFailure
                             | LifetimeRibKind::ConcreteAnonConst(_)
@@ -1515,6 +1520,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                                     // lifetime would be illegal.
                                     LifetimeRibKind::Item
                                     | LifetimeRibKind::AnonymousReportError
+                                    | LifetimeRibKind::AnonymousWarnToStatic(_)
                                     | LifetimeRibKind::ElisionFailure => Some(LifetimeUseSet::Many),
                                     // An anonymous lifetime is legal here, and bound to the right
                                     // place, go ahead.
@@ -1576,7 +1582,8 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                 | LifetimeRibKind::Elided(_)
                 | LifetimeRibKind::Generics { .. }
                 | LifetimeRibKind::ElisionFailure
-                | LifetimeRibKind::AnonymousReportError => {}
+                | LifetimeRibKind::AnonymousReportError
+                | LifetimeRibKind::AnonymousWarnToStatic(_) => {}
             }
         }
 
@@ -1616,6 +1623,25 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     self.record_lifetime_res(lifetime.id, res, elision_candidate);
                     return;
                 }
+                LifetimeRibKind::AnonymousWarnToStatic(node_id) => {
+                    self.record_lifetime_res(lifetime.id, LifetimeRes::Static, elision_candidate);
+                    let msg = if elided {
+                        "`&` without an explicit lifetime name cannot be used here"
+                    } else {
+                        "`'_` cannot be used here"
+                    };
+                    self.r.lint_buffer.buffer_lint_with_diagnostic(
+                        lint::builtin::ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
+                        node_id,
+                        lifetime.ident.span,
+                        msg,
+                        lint::BuiltinLintDiagnostics::AssociatedConstElidedLifetime {
+                            elided,
+                            span: lifetime.ident.span,
+                        },
+                    );
+                    return;
+                }
                 LifetimeRibKind::AnonymousReportError => {
                     let (msg, note) = if elided {
                         (
@@ -1811,7 +1837,8 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     //
                     //     impl Foo for std::cell::Ref<u32> // note lack of '_
                     //     async fn foo(_: std::cell::Ref<u32>) { ... }
-                    LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. } => {
+                    LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. }
+                    | LifetimeRibKind::AnonymousWarnToStatic(_) => {
                         let sess = self.r.tcx.sess;
                         let mut err = rustc_errors::struct_span_err!(
                             sess,
@@ -2898,7 +2925,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
         match &item.kind {
             AssocItemKind::Const(box ast::ConstItem { generics, ty, expr, .. }) => {
                 debug!("resolve_implementation AssocItemKind::Const");
-
                 self.with_generic_param_rib(
                     &generics.params,
                     RibKind::AssocItem,
@@ -2908,28 +2934,33 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                         kind: LifetimeBinderKind::ConstItem,
                     },
                     |this| {
-                        // If this is a trait impl, ensure the const
-                        // exists in trait
-                        this.check_trait_item(
-                            item.id,
-                            item.ident,
-                            &item.kind,
-                            ValueNS,
-                            item.span,
-                            seen_trait_items,
-                            |i, s, c| ConstNotMemberOfTrait(i, s, c),
-                        );
+                        this.with_lifetime_rib(
+                            LifetimeRibKind::AnonymousWarnToStatic(item.id),
+                            |this| {
+                                // If this is a trait impl, ensure the const
+                                // exists in trait
+                                this.check_trait_item(
+                                    item.id,
+                                    item.ident,
+                                    &item.kind,
+                                    ValueNS,
+                                    item.span,
+                                    seen_trait_items,
+                                    |i, s, c| ConstNotMemberOfTrait(i, s, c),
+                                );
 
-                        this.visit_generics(generics);
-                        this.visit_ty(ty);
-                        if let Some(expr) = expr {
-                            // We allow arbitrary const expressions inside of associated consts,
-                            // even if they are potentially not const evaluatable.
-                            //
-                            // Type parameters can already be used and as associated consts are
-                            // not used as part of the type system, this is far less surprising.
-                            this.resolve_const_body(expr, None);
-                        }
+                                this.visit_generics(generics);
+                                this.visit_ty(ty);
+                                if let Some(expr) = expr {
+                                    // We allow arbitrary const expressions inside of associated consts,
+                                    // even if they are potentially not const evaluatable.
+                                    //
+                                    // Type parameters can already be used and as associated consts are
+                                    // not used as part of the type system, this is far less surprising.
+                                    this.resolve_const_body(expr, None);
+                                }
+                            },
+                        );
                     },
                 );
             }

compiler/rustc_session/messages.ftl

@@ -8,6 +8,9 @@ session_cannot_mix_and_match_sanitizers = `-Zsanitizer={$first}` is incompatible
 session_cgu_not_recorded =
     CGU-reuse for `{$cgu_user_name}` is (mangled: `{$cgu_name}`) was not recorded
 
+session_cli_feature_diagnostic_help =
+    add `-Zcrate-attr="feature({$feature})"` to the command-line options to enable
+
 session_crate_name_does_not_match = `--crate-name` and `#[crate_name]` are required to match, but `{$s}` != `{$name}`
 
 session_crate_name_empty = crate name must not be empty

compiler/rustc_session/src/errors.rs

@@ -57,6 +57,12 @@ pub struct FeatureDiagnosticHelp {
     pub feature: Symbol,
 }
 
+#[derive(Subdiagnostic)]
+#[help(session_cli_feature_diagnostic_help)]
+pub struct CliFeatureDiagnosticHelp {
+    pub feature: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(session_not_circumvent_feature)]
 pub struct NotCircumventFeature;