Auto merge of #120877 - matthiaskrgr:rollup-j1b8mv6, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #117614 (static mut: allow mutable reference to arbitrary types, not just slices and arrays)
 - #120719 (Remove support for `associated_type_bound` nested in `dyn` types)
 - #120764 (Add documentation on `str::starts_with`)
 - #120823 (Clarify that atomic and regular integers can differ in alignment)
 - #120859 (Loosen an assertion to account for stashed errors.)
 - #120865 (Turn the "no saved object file in work product" ICE into a translatable fatal error)
 - #120866 (Remove unnecessary `#![feature(min_specialization)]`)
 - #120870 (Allow restricted trait impls under `#[allow_internal_unstable(min_specialization)]`)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: compiler/rustc_ast/src/lib.rs

@@ -15,7 +15,7 @@
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(negative_impls)]
 #![feature(stmt_expr_attributes)]
 

Diff for: compiler/rustc_ast_lowering/messages.ftl

@@ -8,6 +8,10 @@ ast_lowering_arbitrary_expression_in_pattern =
 
 ast_lowering_argument = argument
 
+ast_lowering_assoc_ty_binding_in_dyn =
+    associated type bounds are not allowed in `dyn` types
+    .suggestion = use `impl Trait` to introduce a type instead
+
 ast_lowering_assoc_ty_parentheses =
     parenthesized generic arguments cannot be used in associated type constraints
 
@@ -100,9 +104,6 @@ ast_lowering_match_arm_with_no_body =
     `match` arm with no body
     .suggestion = add a body after the pattern
 
-ast_lowering_misplaced_assoc_ty_binding =
-    associated type bounds are only allowed in where clauses and function signatures, not in {$position}
-
 ast_lowering_misplaced_double_dot =
     `..` patterns are not allowed here
     .note = only allowed in tuple, tuple struct, and slice patterns

Diff for: compiler/rustc_ast_lowering/src/errors.rs

@@ -94,11 +94,12 @@ pub struct MisplacedImplTrait<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_lowering_misplaced_assoc_ty_binding)]
-pub struct MisplacedAssocTyBinding<'a> {
+#[diag(ast_lowering_assoc_ty_binding_in_dyn)]
+pub struct MisplacedAssocTyBinding {
     #[primary_span]
     pub span: Span,
-    pub position: DiagnosticArgFromDisplay<'a>,
+    #[suggestion(code = " = impl", applicability = "maybe-incorrect", style = "verbose")]
+    pub suggestion: Option<Span>,
 }
 
 #[derive(Diagnostic, Clone, Copy)]

Diff for: compiler/rustc_ast_lowering/src/lib.rs

@@ -197,7 +197,6 @@ trait ResolverAstLoweringExt {
     fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
     fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
     fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
-    fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId);
 }
 
 impl ResolverAstLoweringExt for ResolverAstLowering {
@@ -256,11 +255,6 @@ impl ResolverAstLoweringExt for ResolverAstLowering {
     fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
         self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
     }
-
-    fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId) {
-        let lifetimes = self.extra_lifetime_params_map.remove(&from).unwrap_or_default();
-        self.extra_lifetime_params_map.insert(to, lifetimes);
-    }
 }
 
 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
@@ -1084,88 +1078,38 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 hir::TypeBindingKind::Equality { term }
             }
             AssocConstraintKind::Bound { bounds } => {
-                enum DesugarKind {
-                    ImplTrait,
-                    Error(ImplTraitPosition),
-                    Bound,
-                }
-
-                // Piggy-back on the `impl Trait` context to figure out the correct behavior.
-                let desugar_kind = match itctx {
-                    // in an argument, RPIT, or TAIT, if we are within a dyn type:
-                    //
-                    //     fn foo(x: dyn Iterator<Item: Debug>)
-                    //
-                    // then desugar to:
-                    //
-                    //     fn foo(x: dyn Iterator<Item = impl Debug>)
-                    //
-                    // This is because dyn traits must have all of their associated types specified.
-                    ImplTraitContext::ReturnPositionOpaqueTy { .. }
-                    | ImplTraitContext::TypeAliasesOpaqueTy { .. }
-                    | ImplTraitContext::Universal
-                        if self.is_in_dyn_type =>
-                    {
-                        DesugarKind::ImplTrait
-                    }
-
-                    ImplTraitContext::Disallowed(position) if self.is_in_dyn_type => {
-                        DesugarKind::Error(position)
-                    }
-
-                    // We are in the parameter position, but not within a dyn type:
-                    //
-                    //     fn foo(x: impl Iterator<Item: Debug>)
-                    //
-                    // so we leave it as is and this gets expanded in astconv to a bound like
-                    // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
-                    // `impl Iterator`.
-                    _ => DesugarKind::Bound,
-                };
-
-                match desugar_kind {
-                    DesugarKind::ImplTrait => {
-                        // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
-                        // constructing the HIR for `impl bounds...` and then lowering that.
-
-                        let impl_trait_node_id = self.next_node_id();
-                        // Shift `impl Trait` lifetime captures from the associated type bound's
-                        // node id to the opaque node id, so that the opaque can actually use
-                        // these lifetime bounds.
-                        self.resolver
-                            .remap_extra_lifetime_params(constraint.id, impl_trait_node_id);
-
-                        self.with_dyn_type_scope(false, |this| {
-                            let node_id = this.next_node_id();
-                            let ty = this.lower_ty(
-                                &Ty {
-                                    id: node_id,
-                                    kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
-                                    span: this.lower_span(constraint.span),
-                                    tokens: None,
-                                },
-                                itctx,
-                            );
+                // Disallow ATB in dyn types
+                if self.is_in_dyn_type {
+                    let suggestion = match itctx {
+                        ImplTraitContext::ReturnPositionOpaqueTy { .. }
+                        | ImplTraitContext::TypeAliasesOpaqueTy { .. }
+                        | ImplTraitContext::Universal => {
+                            let bound_end_span = constraint
+                                .gen_args
+                                .as_ref()
+                                .map_or(constraint.ident.span, |args| args.span());
+                            if bound_end_span.eq_ctxt(constraint.span) {
+                                Some(self.tcx.sess.source_map().next_point(bound_end_span))
+                            } else {
+                                None
+                            }
+                        }
+                        _ => None,
+                    };
 
-                            hir::TypeBindingKind::Equality { term: ty.into() }
-                        })
-                    }
-                    DesugarKind::Bound => {
-                        // Desugar `AssocTy: Bounds` into a type binding where the
-                        // later desugars into a trait predicate.
-                        let bounds = self.lower_param_bounds(bounds, itctx);
+                    let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
+                        span: constraint.span,
+                        suggestion,
+                    });
+                    let err_ty =
+                        &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
+                    hir::TypeBindingKind::Equality { term: err_ty.into() }
+                } else {
+                    // Desugar `AssocTy: Bounds` into a type binding where the
+                    // later desugars into a trait predicate.
+                    let bounds = self.lower_param_bounds(bounds, itctx);
 
-                        hir::TypeBindingKind::Constraint { bounds }
-                    }
-                    DesugarKind::Error(position) => {
-                        let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
-                            span: constraint.span,
-                            position: DiagnosticArgFromDisplay(&position),
-                        });
-                        let err_ty =
-                            &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
-                        hir::TypeBindingKind::Equality { term: err_ty.into() }
-                    }
+                    hir::TypeBindingKind::Constraint { bounds }
                 }
             }
         };

Diff for: compiler/rustc_codegen_llvm/src/lib.rs

@@ -13,7 +13,6 @@
 #![feature(hash_raw_entry)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
 #![feature(impl_trait_in_assoc_type)]
 
 #[macro_use]

Diff for: compiler/rustc_codegen_ssa/messages.ftl

@@ -190,6 +190,8 @@ codegen_ssa_no_module_named =
 
 codegen_ssa_no_natvis_directory = error enumerating natvis directory: {$error}
 
+codegen_ssa_no_saved_object_file = cached cgu {$cgu_name} should have an object file, but doesn't
+
 codegen_ssa_processing_dymutil_failed = processing debug info with `dsymutil` failed: {$status}
     .note = {$output}
 

Diff for: compiler/rustc_codegen_ssa/src/back/write.rs

@@ -913,7 +913,9 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
 
     let object = load_from_incr_comp_dir(
         cgcx.output_filenames.temp_path(OutputType::Object, Some(&module.name)),
-        module.source.saved_files.get("o").expect("no saved object file in work product"),
+        module.source.saved_files.get("o").unwrap_or_else(|| {
+            cgcx.create_dcx().emit_fatal(errors::NoSavedObjectFile { cgu_name: &module.name })
+        }),
     );
     let dwarf_object =
         module.source.saved_files.get("dwo").as_ref().and_then(|saved_dwarf_object_file| {

Diff for: compiler/rustc_codegen_ssa/src/errors.rs

@@ -121,6 +121,12 @@ pub struct NoNatvisDirectory {
     pub error: Error,
 }
 
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_no_saved_object_file)]
+pub struct NoSavedObjectFile<'a> {
+    pub cgu_name: &'a str,
+}
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_copy_path_buf)]
 pub struct CopyPathBuf {

Diff for: compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -449,35 +449,27 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 }
             }
 
-            Rvalue::Ref(_, BorrowKind::Mut { .. }, place) => {
-                let ty = place.ty(self.body, self.tcx).ty;
-                let is_allowed = match ty.kind() {
-                    // Inside a `static mut`, `&mut [...]` is allowed.
-                    ty::Array(..) | ty::Slice(_)
-                        if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
-                    {
-                        true
-                    }
-
-                    // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
-                    // that this is merely a ZST and it is already eligible for promotion.
-                    // This may require an RFC?
-                    /*
-                    ty::Array(_, len) if len.try_eval_target_usize(cx.tcx, cx.param_env) == Some(0)
-                        => true,
-                    */
-                    _ => false,
-                };
+            Rvalue::Ref(_, BorrowKind::Mut { .. }, place)
+            | Rvalue::AddressOf(Mutability::Mut, place) => {
+                // Inside mutable statics, we allow arbitrary mutable references.
+                // We've allowed `static mut FOO = &mut [elements];` for a long time (the exact
+                // reasons why are lost to history), and there is no reason to restrict that to
+                // arrays and slices.
+                let is_allowed =
+                    self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut);
 
                 if !is_allowed {
-                    self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
+                    self.check_mut_borrow(
+                        place.local,
+                        if matches!(rvalue, Rvalue::Ref(..)) {
+                            hir::BorrowKind::Ref
+                        } else {
+                            hir::BorrowKind::Raw
+                        },
+                    );
                 }
             }
 
-            Rvalue::AddressOf(Mutability::Mut, place) => {
-                self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
-            }
-
             Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Fake, place)
             | Rvalue::AddressOf(Mutability::Not, place) => {
                 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(

Diff for: compiler/rustc_errors/src/lib.rs

@@ -7,6 +7,7 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(array_windows)]
@@ -16,7 +17,6 @@
 #![feature(error_reporter)]
 #![feature(extract_if)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]

Diff for: compiler/rustc_hir/src/lib.rs

@@ -5,7 +5,7 @@
 #![feature(associated_type_defaults)]
 #![feature(closure_track_caller)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(variant_count)]

Diff for: compiler/rustc_hir_analysis/src/check/check.rs

@@ -1283,7 +1283,8 @@ fn check_type_alias_type_params_are_used<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalD
     let ty = tcx.type_of(def_id).instantiate_identity();
     if ty.references_error() {
         // If there is already another error, do not emit an error for not using a type parameter.
-        assert!(tcx.dcx().has_errors().is_some());
+        // Without the `stashed_err_count` part this can fail (#120856).
+        assert!(tcx.dcx().has_errors().is_some() || tcx.dcx().stashed_err_count() > 0);
         return;
     }
 

Diff for: compiler/rustc_hir_analysis/src/coherence/mod.rs

@@ -10,7 +10,7 @@ use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
-use rustc_span::ErrorGuaranteed;
+use rustc_span::{sym, ErrorGuaranteed};
 use rustc_trait_selection::traits;
 
 mod builtin;
@@ -70,7 +70,11 @@ fn enforce_trait_manually_implementable(
     if let ty::trait_def::TraitSpecializationKind::AlwaysApplicable =
         tcx.trait_def(trait_def_id).specialization_kind
     {
-        if !tcx.features().specialization && !tcx.features().min_specialization {
+        if !tcx.features().specialization
+            && !tcx.features().min_specialization
+            && !impl_header_span.allows_unstable(sym::specialization)
+            && !impl_header_span.allows_unstable(sym::min_specialization)
+        {
             return Err(tcx.dcx().emit_err(errors::SpecializationTrait { span: impl_header_span }));
         }
     }

Diff for: compiler/rustc_hir_analysis/src/lib.rs

@@ -67,7 +67,7 @@ This API is completely unstable and subject to change.
 #![feature(is_sorted)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(never_type)]
 #![feature(lazy_cell)]
 #![feature(slice_partition_dedup)]

Diff for: compiler/rustc_hir_typeck/src/lib.rs

@@ -5,7 +5,7 @@
 #![feature(try_blocks)]
 #![feature(never_type)]
 #![feature(box_patterns)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(control_flow_enum)]
 
 #[macro_use]

Diff for: compiler/rustc_infer/src/lib.rs

@@ -24,7 +24,7 @@
 #![feature(let_chains)]
 #![feature(if_let_guard)]
 #![feature(iterator_try_collect)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(try_blocks)]
 #![recursion_limit = "512"] // For rustdoc
 

Diff for: compiler/rustc_lint/src/lib.rs

@@ -35,7 +35,6 @@
 #![feature(iter_order_by)]
 #![feature(let_chains)]
 #![feature(trait_upcasting)]
-#![feature(min_specialization)]
 #![feature(rustc_attrs)]
 #![allow(internal_features)]
 

Diff for: compiler/rustc_lint_defs/src/lib.rs

@@ -1,5 +1,3 @@
-#![feature(min_specialization)]
-
 #[macro_use]
 extern crate rustc_macros;
 

Diff for: compiler/rustc_mir_build/src/lib.rs

@@ -9,7 +9,7 @@
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(try_blocks)]
 
 #[macro_use]

Diff for: compiler/rustc_mir_dataflow/src/lib.rs

@@ -2,7 +2,7 @@
 #![feature(box_patterns)]
 #![feature(exact_size_is_empty)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(try_blocks)]
 
 #[macro_use]