Auto merge of #93836 - matthiaskrgr:rollup-d1ssiwl, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #91443 (Better suggestions when user tries to collect into an unsized `[_]`)
 - #91504 (`#[used(linker)]` attribute)
 - #93503 (debuginfo: Fix DW_AT_containing_type vtable debuginfo regression)
 - #93753 (Complete removal of #[main] attribute from compiler)
 - #93799 (Fix typo in `std::fmt` docs)
 - #93813 (Make a few cleanup MIR passes public)

Failed merges:

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

compiler/rustc_codegen_gcc/src/consts.rs

@@ -144,7 +144,7 @@ impl<'gcc, 'tcx> StaticMethods for CodegenCx<'gcc, 'tcx> {
             // TODO(antoyo): set link section.
         }
 
-        if attrs.flags.contains(CodegenFnAttrFlags::USED) {
+        if attrs.flags.contains(CodegenFnAttrFlags::USED) || attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) {
             self.add_used_global(global.to_rvalue());
         }
     }

compiler/rustc_codegen_llvm/src/consts.rs

@@ -522,6 +522,9 @@ impl<'ll> StaticMethods for CodegenCx<'ll, '_> {
             }
 
             if attrs.flags.contains(CodegenFnAttrFlags::USED) {
+                // `USED` and `USED_LINKER` can't be used together.
+                assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER));
+
                 // The semantics of #[used] in Rust only require the symbol to make it into the
                 // object file. It is explicitly allowed for the linker to strip the symbol if it
                 // is dead. As such, use llvm.compiler.used instead of llvm.used.
@@ -530,6 +533,12 @@ impl<'ll> StaticMethods for CodegenCx<'ll, '_> {
                 // in some versions of the gold linker.
                 self.add_compiler_used_global(g);
             }
+            if attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) {
+                // `USED` and `USED_LINKER` can't be used together.
+                assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED));
+
+                self.add_used_global(g);
+            }
         }
     }
 

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -21,6 +21,7 @@ use crate::value::Value;
 
 use cstr::cstr;
 use rustc_codegen_ssa::debuginfo::type_names::cpp_like_debuginfo;
+use rustc_codegen_ssa::debuginfo::type_names::VTableNameKind;
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
@@ -276,6 +277,12 @@ impl<'ll, 'tcx> TypeMap<'ll, 'tcx> {
     ) -> String {
         format!("{}_variant_part", self.get_unique_type_id_as_string(enum_type_id))
     }
+
+    /// Gets the `UniqueTypeId` for the type of a vtable.
+    fn get_unique_type_id_of_vtable_type(&mut self, vtable_type_name: &str) -> UniqueTypeId {
+        let interner_key = self.unique_id_interner.intern(vtable_type_name);
+        interner_key
+    }
 }
 
 /// A description of some recursive type. It can either be already finished (as
@@ -351,14 +358,15 @@ impl<'ll, 'tcx> RecursiveTypeDescription<'ll, 'tcx> {
 
                 // ... then create the member descriptions ...
                 let member_descriptions = member_description_factory.create_member_descriptions(cx);
+                let type_params = compute_type_parameters(cx, unfinished_type);
 
                 // ... and attach them to the stub to complete it.
                 set_members_of_composite_type(
                     cx,
-                    unfinished_type,
                     member_holding_stub,
                     member_descriptions,
                     None,
+                    type_params,
                 );
                 MetadataCreationResult::new(metadata_stub, true)
             }
@@ -983,7 +991,17 @@ fn foreign_type_metadata<'ll, 'tcx>(
     debug!("foreign_type_metadata: {:?}", t);
 
     let name = compute_debuginfo_type_name(cx.tcx, t, false);
-    create_struct_stub(cx, t, &name, unique_type_id, NO_SCOPE_METADATA, DIFlags::FlagZero)
+    let (size, align) = cx.size_and_align_of(t);
+    create_struct_stub(
+        cx,
+        size,
+        align,
+        &name,
+        unique_type_id,
+        NO_SCOPE_METADATA,
+        DIFlags::FlagZero,
+        None,
+    )
 }
 
 fn param_type_metadata<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll DIType {
@@ -1299,14 +1317,17 @@ fn prepare_struct_metadata<'ll, 'tcx>(
     };
 
     let containing_scope = get_namespace_for_item(cx, struct_def_id);
+    let (size, align) = cx.size_and_align_of(struct_type);
 
     let struct_metadata_stub = create_struct_stub(
         cx,
-        struct_type,
+        size,
+        align,
         &struct_name,
         unique_type_id,
         Some(containing_scope),
         DIFlags::FlagZero,
+        None,
     );
 
     create_and_register_recursive_type_forward_declaration(
@@ -1398,15 +1419,18 @@ fn prepare_tuple_metadata<'ll, 'tcx>(
     unique_type_id: UniqueTypeId,
     containing_scope: Option<&'ll DIScope>,
 ) -> RecursiveTypeDescription<'ll, 'tcx> {
+    let (size, align) = cx.size_and_align_of(tuple_type);
     let tuple_name = compute_debuginfo_type_name(cx.tcx, tuple_type, false);
 
     let struct_stub = create_struct_stub(
         cx,
-        tuple_type,
+        size,
+        align,
         &tuple_name[..],
         unique_type_id,
         containing_scope,
         DIFlags::FlagZero,
+        None,
     );
 
     create_and_register_recursive_type_forward_declaration(
@@ -1581,13 +1605,14 @@ impl<'ll, 'tcx> EnumMemberDescriptionFactory<'ll, 'tcx> {
                     describe_enum_variant(cx, self.layout, variant_info, self_metadata);
 
                 let member_descriptions = member_description_factory.create_member_descriptions(cx);
+                let type_params = compute_type_parameters(cx, self.enum_type);
 
                 set_members_of_composite_type(
                     cx,
-                    self.enum_type,
                     variant_type_metadata,
                     member_descriptions,
                     Some(&self.common_members),
+                    type_params,
                 );
                 vec![MemberDescription {
                     name: variant_info.variant_name(),
@@ -1648,13 +1673,14 @@ impl<'ll, 'tcx> EnumMemberDescriptionFactory<'ll, 'tcx> {
 
                         let member_descriptions =
                             member_desc_factory.create_member_descriptions(cx);
+                        let type_params = compute_type_parameters(cx, self.enum_type);
 
                         set_members_of_composite_type(
                             cx,
-                            self.enum_type,
                             variant_type_metadata,
                             member_descriptions,
                             Some(&self.common_members),
+                            type_params,
                         );
 
                         MemberDescription {
@@ -1777,13 +1803,14 @@ impl<'ll, 'tcx> EnumMemberDescriptionFactory<'ll, 'tcx> {
                     );
 
                     let member_descriptions = member_desc_factory.create_member_descriptions(cx);
+                    let type_params = compute_type_parameters(cx, self.enum_type);
 
                     set_members_of_composite_type(
                         cx,
-                        self.enum_type,
                         variant_type_metadata,
                         member_descriptions,
                         Some(&self.common_members),
+                        type_params,
                     );
 
                     let (size, align) =
@@ -1823,13 +1850,14 @@ impl<'ll, 'tcx> EnumMemberDescriptionFactory<'ll, 'tcx> {
 
                             let member_descriptions =
                                 member_desc_factory.create_member_descriptions(cx);
+                            let type_params = compute_type_parameters(cx, self.enum_type);
 
                             set_members_of_composite_type(
                                 cx,
-                                self.enum_type,
                                 variant_type_metadata,
                                 member_descriptions,
                                 Some(&self.common_members),
+                                type_params,
                             );
 
                             let niche_value = calculate_niche_value(i);
@@ -1965,13 +1993,18 @@ fn describe_enum_variant<'ll, 'tcx>(
             .type_map
             .borrow_mut()
             .get_unique_type_id_of_enum_variant(cx, layout.ty, variant_name);
+
+        let (size, align) = cx.size_and_align_of(layout.ty);
+
         create_struct_stub(
             cx,
-            layout.ty,
+            size,
+            align,
             variant_name,
             unique_type_id,
             Some(containing_scope),
             DIFlags::FlagZero,
+            None,
         )
     });
 
@@ -2308,22 +2341,27 @@ fn composite_type_metadata<'ll, 'tcx>(
     member_descriptions: Vec<MemberDescription<'ll>>,
     containing_scope: Option<&'ll DIScope>,
 ) -> &'ll DICompositeType {
+    let (size, align) = cx.size_and_align_of(composite_type);
+
     // Create the (empty) struct metadata node ...
     let composite_type_metadata = create_struct_stub(
         cx,
-        composite_type,
+        size,
+        align,
         composite_type_name,
         composite_type_unique_id,
         containing_scope,
         DIFlags::FlagZero,
+        None,
     );
+
     // ... and immediately create and add the member descriptions.
     set_members_of_composite_type(
         cx,
-        composite_type,
         composite_type_metadata,
         member_descriptions,
         None,
+        compute_type_parameters(cx, composite_type),
     );
 
     composite_type_metadata
@@ -2331,10 +2369,10 @@ fn composite_type_metadata<'ll, 'tcx>(
 
 fn set_members_of_composite_type<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
-    composite_type: Ty<'tcx>,
     composite_type_metadata: &'ll DICompositeType,
     member_descriptions: Vec<MemberDescription<'ll>>,
     common_members: Option<&Vec<Option<&'ll DIType>>>,
+    type_params: &'ll DIArray,
 ) {
     // In some rare cases LLVM metadata uniquing would lead to an existing type
     // description being used instead of a new one created in
@@ -2361,13 +2399,12 @@ fn set_members_of_composite_type<'ll, 'tcx>(
         member_metadata.extend(other_members.iter());
     }
 
-    let type_params = compute_type_parameters(cx, composite_type);
     unsafe {
-        let type_array = create_DIArray(DIB(cx), &member_metadata);
+        let field_array = create_DIArray(DIB(cx), &member_metadata);
         llvm::LLVMRustDICompositeTypeReplaceArrays(
             DIB(cx),
             composite_type_metadata,
-            Some(type_array),
+            Some(field_array),
             Some(type_params),
         );
     }
@@ -2420,14 +2457,14 @@ fn compute_type_parameters<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, ty: Ty<'tcx>) -
 /// with `set_members_of_composite_type()`.
 fn create_struct_stub<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
-    struct_type: Ty<'tcx>,
+    size: Size,
-    struct_type_name: &str,
+    align: Align,
+    type_name: &str,
     unique_type_id: UniqueTypeId,
     containing_scope: Option<&'ll DIScope>,
     flags: DIFlags,
+    vtable_holder: Option<&'ll DIType>,
 ) -> &'ll DICompositeType {
-    let (struct_size, struct_align) = cx.size_and_align_of(struct_type);
-
     let type_map = debug_context(cx).type_map.borrow();
     let unique_type_id = type_map.get_unique_type_id_as_string(unique_type_id);
 
@@ -2440,17 +2477,17 @@ fn create_struct_stub<'ll, 'tcx>(
         llvm::LLVMRustDIBuilderCreateStructType(
             DIB(cx),
             containing_scope,
-            struct_type_name.as_ptr().cast(),
+            type_name.as_ptr().cast(),
-            struct_type_name.len(),
+            type_name.len(),
             unknown_file_metadata(cx),
             UNKNOWN_LINE_NUMBER,
-            struct_size.bits(),
+            size.bits(),
-            struct_align.bits() as u32,
+            align.bits() as u32,
             flags,
             None,
             empty_array,
             0,
-            None,
+            vtable_holder,
             unique_type_id.as_ptr().cast(),
             unique_type_id.len(),
         )
@@ -2556,6 +2593,14 @@ pub fn create_global_var_metadata<'ll>(cx: &CodegenCx<'ll, '_>, def_id: DefId, g
 }
 
 /// Generates LLVM debuginfo for a vtable.
+///
+/// The vtable type looks like a struct with a field for each function pointer and super-trait
+/// pointer it contains (plus the `size` and `align` fields).
+///
+/// Except for `size`, `align`, and `drop_in_place`, the field names don't try to mirror
+/// the name of the method they implement. This can be implemented in the future once there
+/// is a proper disambiguation scheme for dealing with methods from different traits that have
+/// the same name.
 fn vtable_type_metadata<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     ty: Ty<'tcx>,
@@ -2572,16 +2617,81 @@ fn vtable_type_metadata<'ll, 'tcx>(
         COMMON_VTABLE_ENTRIES
     };
 
-    // FIXME: We describe the vtable as an array of *const () pointers. The length of the array is
+    // All function pointers are described as opaque pointers. This could be improved in the future
-    //        correct - but we could create a more accurate description, e.g. by describing it
+    // by describing them as actual function pointers.
-    //        as a struct where each field has a name that corresponds to the name of the method
+    let void_pointer_ty = tcx.mk_imm_ptr(tcx.types.unit);
-    //        it points to.
+    let void_pointer_type_debuginfo = type_metadata(cx, void_pointer_ty);
-    //        However, this is not entirely straightforward because there might be multiple
+    let usize_debuginfo = type_metadata(cx, tcx.types.usize);
-    //        methods with the same name if the vtable is for multiple traits. So for now we keep
+    let (pointer_size, pointer_align) = cx.size_and_align_of(void_pointer_ty);
-    //        things simple instead of adding some ad-hoc disambiguation scheme.
+    // If `usize` is not pointer-sized and -aligned then the size and alignment computations
-    let vtable_type = tcx.mk_array(tcx.mk_imm_ptr(tcx.types.unit), vtable_entries.len() as u64);
+    // for the vtable as a whole would be wrong. Let's make sure this holds even on weird
+    // platforms.
+    assert_eq!(cx.size_and_align_of(tcx.types.usize), (pointer_size, pointer_align));
 
-    type_metadata(cx, vtable_type)
+    let vtable_type_name =
+        compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::Type);
+    let unique_type_id = debug_context(cx)
+        .type_map
+        .borrow_mut()
+        .get_unique_type_id_of_vtable_type(&vtable_type_name);
+    let size = pointer_size * vtable_entries.len() as u64;
+
+    // This gets mapped to a DW_AT_containing_type attribute which allows GDB to correlate
+    // the vtable to the type it is for.
+    let vtable_holder = type_metadata(cx, ty);
+
+    let vtable_type_metadata = create_struct_stub(
+        cx,
+        size,
+        pointer_align,
+        &vtable_type_name,
+        unique_type_id,
+        NO_SCOPE_METADATA,
+        DIFlags::FlagArtificial,
+        Some(vtable_holder),
+    );
+
+    // Create a field for each entry in the vtable.
+    let fields: Vec<_> = vtable_entries
+        .iter()
+        .enumerate()
+        .filter_map(|(index, vtable_entry)| {
+            let (field_name, field_type) = match vtable_entry {
+                ty::VtblEntry::MetadataDropInPlace => {
+                    ("drop_in_place".to_string(), void_pointer_type_debuginfo)
+                }
+                ty::VtblEntry::Method(_) => {
+                    // Note: This code does not try to give a proper name to each method
+                    //       because there might be multiple methods with the same name
+                    //       (coming from different traits).
+                    (format!("__method{}", index), void_pointer_type_debuginfo)
+                }
+                ty::VtblEntry::TraitVPtr(_) => {
+                    // Note: In the future we could try to set the type of this pointer
+                    //       to the type that we generate for the corresponding vtable.
+                    (format!("__super_trait_ptr{}", index), void_pointer_type_debuginfo)
+                }
+                ty::VtblEntry::MetadataAlign => ("align".to_string(), usize_debuginfo),
+                ty::VtblEntry::MetadataSize => ("size".to_string(), usize_debuginfo),
+                ty::VtblEntry::Vacant => return None,
+            };
+
+            Some(MemberDescription {
+                name: field_name,
+                type_metadata: field_type,
+                offset: pointer_size * index as u64,
+                size: pointer_size,
+                align: pointer_align,
+                flags: DIFlags::FlagZero,
+                discriminant: None,
+                source_info: None,
+            })
+        })
+        .collect();
+
+    let type_params = create_DIArray(DIB(cx), &[]);
+    set_members_of_composite_type(cx, vtable_type_metadata, fields, None, type_params);
+    vtable_type_metadata
 }
 
 /// Creates debug information for the given vtable, which is for the
@@ -2603,11 +2713,12 @@ pub fn create_vtable_metadata<'ll, 'tcx>(
         return;
     }
 
-    let vtable_name = compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref);
+    let vtable_name =
+        compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::GlobalVariable);
     let vtable_type = vtable_type_metadata(cx, ty, poly_trait_ref);
+    let linkage_name = "";
 
     unsafe {
-        let linkage_name = "";
         llvm::LLVMRustDIBuilderCreateStaticVariable(
             DIB(cx),
             NO_SCOPE_METADATA,

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -469,7 +469,14 @@ fn push_debuginfo_type_name<'tcx>(
     }
 }
 
-/// Computes a name for the global variable storing a vtable.
+pub enum VTableNameKind {
+    // Is the name for the const/static holding the vtable?
+    GlobalVariable,
+    // Is the name for the type of the vtable?
+    Type,
+}
+
+/// Computes a name for the global variable storing a vtable (or the type of that global variable).
 ///
 /// The name is of the form:
 ///
@@ -478,10 +485,15 @@ fn push_debuginfo_type_name<'tcx>(
 /// or, when generating C++-like names:
 ///
 /// `impl$<path::to::SomeType, path::to::SomeTrait>::vtable$`
+///
+/// If `kind` is `VTableNameKind::Type` then the last component is `{vtable_ty}` instead of just
+/// `{vtable}`, so that the type and the corresponding global variable get assigned different
+/// names.
 pub fn compute_debuginfo_vtable_name<'tcx>(
     tcx: TyCtxt<'tcx>,
     t: Ty<'tcx>,
     trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    kind: VTableNameKind,
 ) -> String {
     let cpp_like_debuginfo = cpp_like_debuginfo(tcx);
 
@@ -514,7 +526,12 @@ pub fn compute_debuginfo_vtable_name<'tcx>(
 
     push_close_angle_bracket(cpp_like_debuginfo, &mut vtable_name);
 
-    let suffix = if cpp_like_debuginfo { "::vtable$" } else { "::{vtable}" };
+    let suffix = match (cpp_like_debuginfo, kind) {
+        (true, VTableNameKind::GlobalVariable) => "::vtable$",
+        (false, VTableNameKind::GlobalVariable) => "::{vtable}",
+        (true, VTableNameKind::Type) => "::vtable_type$",
+        (false, VTableNameKind::Type) => "::{vtable_type}",
+    };
 
     vtable_name.reserve_exact(suffix.len());
     vtable_name.push_str(suffix);

compiler/rustc_feature/src/active.rs

@@ -531,6 +531,8 @@ declare_features! (
     ///
     /// NOTE: A limited form of `union U { ... }` was accepted in 1.19.0.
     (active, untagged_unions, "1.13.0", Some(55149), None),
+    /// Allows using the `#[used(linker)]` (or `#[used(compiler)]`) attribute.
+    (active, used_with_arg, "1.60.0", Some(93798), None),
     /// Allows `extern "wasm" fn`
     (active, wasm_abi, "1.53.0", Some(83788), None),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!

compiler/rustc_feature/src/builtin_attrs.rs

@@ -324,7 +324,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ungated!(export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
     ungated!(link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
     ungated!(no_mangle, Normal, template!(Word), WarnFollowing),
-    ungated!(used, Normal, template!(Word), WarnFollowing),
+    ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing),
 
     // Limits:
     ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
@@ -339,7 +339,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Entry point:
-    ungated!(main, Normal, template!(Word), WarnFollowing),
     ungated!(start, Normal, template!(Word), WarnFollowing),
     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing),
     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing),

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -89,6 +89,8 @@ bitflags! {
         /// the MIR `InstrumentCoverage` pass and not added to the coverage map
         /// during codegen.
         const NO_COVERAGE               = 1 << 15;
+        /// `#[used(linker)]`: indicates that LLVM nor the linker can eliminate this function.
+        const USED_LINKER               = 1 << 16;
     }
 }
 

compiler/rustc_mir_transform/src/lib.rs

@@ -43,7 +43,8 @@ mod add_retag;
 mod check_const_item_mutation;
 mod check_packed_ref;
 pub mod check_unsafety;
-mod cleanup_post_borrowck;
+// This pass is public to allow external drivers to perform MIR cleanup
+pub mod cleanup_post_borrowck;
 mod const_debuginfo;
 mod const_goto;
 mod const_prop;
@@ -65,7 +66,8 @@ mod match_branches;
 mod multiple_return_terminators;
 mod normalize_array_len;
 mod nrvo;
-mod remove_false_edges;
+// This pass is public to allow external drivers to perform MIR cleanup
+pub mod remove_false_edges;
 mod remove_noop_landing_pads;
 mod remove_storage_markers;
 mod remove_uninit_drops;
@@ -75,7 +77,8 @@ mod required_consts;
 mod reveal_all;
 mod separate_const_switch;
 mod shim;
-mod simplify;
+// This pass is public to allow external drivers to perform MIR cleanup
+pub mod simplify;
 mod simplify_branches;
 mod simplify_comparison_integral;
 mod simplify_try;

compiler/rustc_passes/src/check_attr.rs

@@ -1741,12 +1741,46 @@ impl CheckAttrVisitor<'_> {
     }
 
     fn check_used(&self, attrs: &[Attribute], target: Target) {
+        let mut used_linker_span = None;
+        let mut used_compiler_span = None;
         for attr in attrs {
             if attr.has_name(sym::used) && target != Target::Static {
                 self.tcx
                     .sess
                     .span_err(attr.span, "attribute must be applied to a `static` variable");
             }
+            let inner = attr.meta_item_list();
+            match inner.as_deref() {
+                Some([item]) if item.has_name(sym::linker) => {
+                    if used_linker_span.is_none() {
+                        used_linker_span = Some(attr.span);
+                    }
+                }
+                Some([item]) if item.has_name(sym::compiler) => {
+                    if used_compiler_span.is_none() {
+                        used_compiler_span = Some(attr.span);
+                    }
+                }
+                Some(_) => {
+                    // This error case is handled in rustc_typeck::collect.
+                }
+                None => {
+                    // Default case (compiler) when arg isn't defined.
+                    if used_compiler_span.is_none() {
+                        used_compiler_span = Some(attr.span);
+                    }
+                }
+            }
+        }
+        if let (Some(linker_span), Some(compiler_span)) = (used_linker_span, used_compiler_span) {
+            let spans = vec![linker_span, compiler_span];
+            self.tcx
+                .sess
+                .struct_span_err(
+                    spans,
+                    "`used(compiler)` and `used(linker)` can't be used together",
+                )
+                .emit();
         }
     }
 

compiler/rustc_passes/src/dead.rs

@@ -466,7 +466,10 @@ fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
 
     // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
     // forcefully, e.g., for placing it in a specific section.
-    if cg_attrs.contains_extern_indicator() || cg_attrs.flags.contains(CodegenFnAttrFlags::USED) {
+    if cg_attrs.contains_extern_indicator()
+        || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
+        || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
+    {
         return true;
     }
 

compiler/rustc_span/src/symbol.rs

@@ -449,6 +449,7 @@ symbols! {
         compare_exchange_weak,
         compile_error,
         compile_error_macro,
+        compiler,
         compiler_builtins,
         compiler_fence,
         concat,
@@ -668,6 +669,7 @@ symbols! {
         fill,
         finish,
         flags,
+        float,
         float_to_int_unchecked,
         floorf32,
         floorf64,
@@ -771,6 +773,8 @@ symbols! {
         inline_const_pat,
         inout,
         instruction_set,
+        integer_: "integer",
+        integral,
         intel,
         into_future,
         into_iter,
@@ -815,6 +819,7 @@ symbols! {
         link_ordinal,
         link_section,
         linkage,
+        linker,
         lint_reasons,
         literal,
         load,
@@ -1463,6 +1468,7 @@ symbols! {
         use_extern_macros,
         use_nested_groups,
         used,
+        used_with_arg,
         usize,
         v1,
         va_arg,

compiler/rustc_trait_selection/src/traits/on_unimplemented.rs

@@ -62,6 +62,10 @@ impl<'tcx> OnUnimplementedDirective {
         let mut errored = false;
         let mut item_iter = items.iter();
 
+        let parse_value = |value_str| {
+            OnUnimplementedFormatString::try_parse(tcx, trait_def_id, value_str, span).map(Some)
+        };
+
         let condition = if is_root {
             None
         } else {
@@ -86,7 +90,14 @@ impl<'tcx> OnUnimplementedDirective {
                         None,
                     )
                 })?;
-            attr::eval_condition(cond, &tcx.sess.parse_sess, Some(tcx.features()), &mut |_| true);
+            attr::eval_condition(cond, &tcx.sess.parse_sess, Some(tcx.features()), &mut |item| {
+                if let Some(symbol) = item.value_str() {
+                    if parse_value(symbol).is_err() {
+                        errored = true;
+                    }
+                }
+                true
+            });
             Some(cond.clone())
         };
 
@@ -97,10 +108,6 @@ impl<'tcx> OnUnimplementedDirective {
         let mut subcommands = vec![];
         let mut append_const_msg = None;
 
-        let parse_value = |value_str| {
-            OnUnimplementedFormatString::try_parse(tcx, trait_def_id, value_str, span).map(Some)
-        };
-
         for item in item_iter {
             if item.has_name(sym::message) && message.is_none() {
                 if let Some(message_) = item.value_str() {
@@ -221,6 +228,9 @@ impl<'tcx> OnUnimplementedDirective {
         let mut append_const_msg = None;
         info!("evaluate({:?}, trait_ref={:?}, options={:?})", self, trait_ref, options);
 
+        let options_map: FxHashMap<Symbol, String> =
+            options.iter().filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned()))).collect();
+
         for command in self.subcommands.iter().chain(Some(self)).rev() {
             if let Some(ref condition) = command.condition {
                 if !attr::eval_condition(
@@ -229,7 +239,11 @@ impl<'tcx> OnUnimplementedDirective {
                     Some(tcx.features()),
                     &mut |c| {
                         c.ident().map_or(false, |ident| {
-                            options.contains(&(ident.name, c.value_str().map(|s| s.to_string())))
+                            let value = c.value_str().map(|s| {
+                                OnUnimplementedFormatString(s).format(tcx, trait_ref, &options_map)
+                            });
+
+                            options.contains(&(ident.name, value))
                         })
                     },
                 ) {
@@ -257,13 +271,11 @@ impl<'tcx> OnUnimplementedDirective {
             append_const_msg = command.append_const_msg.clone();
         }
 
-        let options: FxHashMap<Symbol, String> =
-            options.iter().filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned()))).collect();
         OnUnimplementedNote {
-            label: label.map(|l| l.format(tcx, trait_ref, &options)),
+            label: label.map(|l| l.format(tcx, trait_ref, &options_map)),
-            message: message.map(|m| m.format(tcx, trait_ref, &options)),
+            message: message.map(|m| m.format(tcx, trait_ref, &options_map)),
-            note: note.map(|n| n.format(tcx, trait_ref, &options)),
+            note: note.map(|n| n.format(tcx, trait_ref, &options_map)),
-            enclosing_scope: enclosing_scope.map(|e_s| e_s.format(tcx, trait_ref, &options)),
+            enclosing_scope: enclosing_scope.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
             append_const_msg,
         }
     }
@@ -306,6 +318,12 @@ impl<'tcx> OnUnimplementedFormatString {
                     Position::ArgumentNamed(s) if s == sym::from_desugaring => (),
                     // `{ItemContext}` is allowed
                     Position::ArgumentNamed(s) if s == sym::ItemContext => (),
+                    // `{integral}` and `{integer}` and `{float}` are allowed
+                    Position::ArgumentNamed(s)
+                        if s == sym::integral || s == sym::integer_ || s == sym::float =>
+                    {
+                        ()
+                    }
                     // So is `{A}` if A is a type parameter
                     Position::ArgumentNamed(s) => {
                         match generics.params.iter().find(|param| param.name == s) {
@@ -385,6 +403,12 @@ impl<'tcx> OnUnimplementedFormatString {
                                 &empty_string
                             } else if s == sym::ItemContext {
                                 &item_context
+                            } else if s == sym::integral {
+                                "{integral}"
+                            } else if s == sym::integer_ {
+                                "{integer}"
+                            } else if s == sym::float {
+                                "{float}"
                             } else {
                                 bug!(
                                     "broken on_unimplemented {:?} for {:?}: \

compiler/rustc_typeck/src/collect.rs

@@ -1,3 +1,4 @@
+// ignore-tidy-filelength
 //! "Collection" is the process of determining the type and other external
 //! details of each item in Rust. Collection is specifically concerned
 //! with *inter-procedural* things -- for example, for a function
@@ -2856,7 +2857,42 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         } else if attr.has_name(sym::rustc_std_internal_symbol) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
         } else if attr.has_name(sym::used) {
-            codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
+            let inner = attr.meta_item_list();
+            match inner.as_deref() {
+                Some([item]) if item.has_name(sym::linker) => {
+                    if !tcx.features().used_with_arg {
+                        feature_err(
+                            &tcx.sess.parse_sess,
+                            sym::used_with_arg,
+                            attr.span,
+                            "`#[used(linker)]` is currently unstable",
+                        )
+                        .emit();
+                    }
+                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER;
+                }
+                Some([item]) if item.has_name(sym::compiler) => {
+                    if !tcx.features().used_with_arg {
+                        feature_err(
+                            &tcx.sess.parse_sess,
+                            sym::used_with_arg,
+                            attr.span,
+                            "`#[used(compiler)]` is currently unstable",
+                        )
+                        .emit();
+                    }
+                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
+                }
+                Some(_) => {
+                    tcx.sess
+                        .struct_span_err(
+                            attr.span,
+                            "expected `used`, `used(compiler)` or `used(linker)`",
+                        )
+                        .emit();
+                }
+                None => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED,
+            }
         } else if attr.has_name(sym::cmse_nonsecure_entry) {
             if !matches!(tcx.fn_sig(id).abi(), abi::Abi::C { .. }) {
                 struct_span_err!(

library/alloc/src/fmt.rs

@@ -74,7 +74,7 @@
 //! identifier '=' expression
 //! ```
 //!
-//! For example, the following [`format!`] expressions all use named argument:
+//! For example, the following [`format!`] expressions all use named arguments:
 //!
 //! ```
 //! format!("{argument}", argument = "test");   // => "test"

library/core/src/iter/traits/collect.rs

@@ -81,6 +81,32 @@
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
+    on(
+        _Self = "[{A}]",
+        message = "a value of type `{Self}` cannot be built since `{Self}` has no definite size",
+        label = "try explicitly collecting into a `Vec<{A}>`",
+    ),
+    on(
+        all(
+            A = "{integer}",
+            any(
+                _Self = "[i8]",
+                _Self = "[i16]",
+                _Self = "[i32]",
+                _Self = "[i64]",
+                _Self = "[i128]",
+                _Self = "[isize]",
+                _Self = "[u8]",
+                _Self = "[u16]",
+                _Self = "[u32]",
+                _Self = "[u64]",
+                _Self = "[u128]",
+                _Self = "[usize]"
+            )
+        ),
+        message = "a value of type `{Self}` cannot be built since `{Self}` has no definite size",
+        label = "try explicitly collecting into a `Vec<{A}>`",
+    ),
     message = "a value of type `{Self}` cannot be built from an iterator \
                over elements of type `{A}`",
     label = "value of type `{Self}` cannot be built from `std::iter::Iterator<Item={A}>`"

src/test/codegen/debug-vtable.rs

@@ -9,19 +9,41 @@
 // compile-flags: -Cdebuginfo=2 -Copt-level=0 -Csymbol-mangling-version=v0
 // ignore-tidy-linelength
 
+// NONMSVC: ![[USIZE:[0-9]+]] = !DIBasicType(name: "usize"
+// MSVC: ![[USIZE:[0-9]+]] = !DIDerivedType(tag: DW_TAG_typedef, name: "usize"
+// NONMSVC: ![[PTR:[0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()"
+// MSVC: ![[PTR:[0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_const$<tuple$<> >"
+
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as debug_vtable::SomeTrait>::{vtable}"
 // MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, debug_vtable::SomeTrait>::vtable$"
-// NONMSVC: !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const ()",
+
-// MSVC: !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_const$<tuple$<> >",
+// NONMSVC: ![[VTABLE_TY0:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as debug_vtable::SomeTrait>::{vtable_type}", {{.*}} size: {{320|160}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}} vtableHolder: ![[FOO_TYPE:[0-9]+]],
-// CHECK: !DISubrange(count: 5
+// MSVC: ![[VTABLE_TY0:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, debug_vtable::SomeTrait>::vtable_type$", {{.*}} size: {{320|160}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}} vtableHolder: ![[FOO_TYPE:[0-9]+]],
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method3", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{192|96}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method4", scope: ![[VTABLE_TY0]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{256|128}})
+// CHECK: ![[FOO_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Foo",
 
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as debug_vtable::SomeTraitWithGenerics<u64, i8>>::{vtable}"
 // MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, debug_vtable::SomeTraitWithGenerics<u64,i8> >::vtable$"
-// CHECK: !DISubrange(count: 4
+
+// NONMSVC: ![[VTABLE_TY1:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as debug_vtable::SomeTraitWithGenerics<u64, i8>>::{vtable_type}", {{.*}}, size: {{256|128}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
+// MSVC: ![[VTABLE_TY1:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, debug_vtable::SomeTraitWithGenerics<u64,i8> >::vtable_type$", {{.*}}, size: {{256|128}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__method3", scope: ![[VTABLE_TY1]], {{.*}} baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}}, offset: {{192|96}})
 
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::Foo as _>::{vtable}"
 // MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::Foo, _>::vtable$"
-// CHECK: !DISubrange(count: 3
+
+// NONMSVC: ![[VTABLE_TY2:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "<debug_vtable::Foo as _>::{vtable_type}", {{.*}}, size: {{192|96}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
+// MSVC: ![[VTABLE_TY2:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<debug_vtable::Foo, _>::vtable_type$", {{.*}}, size: {{192|96}}, align: {{64|32}}, flags: DIFlagArtificial, {{.*}}, vtableHolder: ![[FOO_TYPE]],
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[PTR]], size: {{64|32}}, align: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "size", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{64|32}})
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
 
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::bar::{closure_env#0} as core::ops::function::FnOnce<(core::option::Option<&dyn core::ops::function::Fn<(), Output=()>>)>>::{vtable}"
 // MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::bar::closure_env$0, core::ops::function::FnOnce<tuple$<enum$<core::option::Option<ref$<dyn$<core::ops::function::Fn<tuple$<>,assoc$<Output,tuple$<> > > > > >, {{.*}}, {{.*}}, Some> > > >::vtable$"
@@ -34,6 +56,9 @@
 
 #![crate_type = "lib"]
 
+// Force emission for debuginfo for usize and *const() early..
+pub static mut XYZ: Option<(usize, *const ())> = None;
+
 pub struct Foo;
 
 pub trait SomeTrait {

src/test/codegen/debuginfo-generic-closure-env-names.rs

@@ -17,35 +17,34 @@
 
 // compile-flags: -Cdebuginfo=2 --edition 2021 -Copt-level=0 -Csymbol-mangling-version=v0
 
-
-// CHECK: [[non_generic_closure_NAMESPACE:!.*]] = !DINamespace(name: "non_generic_closure"
-// CHECK: [[function_containing_closure_NAMESPACE:!.*]] = !DINamespace(name: "function_containing_closure"
-// CHECK: [[generic_async_function_NAMESPACE:!.*]] = !DINamespace(name: "generic_async_function"
-// CHECK: [[generic_async_block_NAMESPACE:!.*]] = !DINamespace(name: "generic_async_block"
-
 // non_generic_closure()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}", scope: [[non_generic_closure_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}", scope: ![[non_generic_closure_NAMESPACE:[0-9]+]],
-// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0", scope: [[non_generic_closure_NAMESPACE]]
+// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0", scope: ![[non_generic_closure_NAMESPACE:[0-9]+]],
+// CHECK: ![[non_generic_closure_NAMESPACE]] = !DINamespace(name: "non_generic_closure"
+
+// CHECK: ![[function_containing_closure_NAMESPACE:[0-9]+]] = !DINamespace(name: "function_containing_closure"
+// CHECK: ![[generic_async_function_NAMESPACE:[0-9]+]] = !DINamespace(name: "generic_async_function"
+// CHECK: ![[generic_async_block_NAMESPACE:[0-9]+]] = !DINamespace(name: "generic_async_block"
 
 // function_containing_closure<u32>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<u32>", scope: [[function_containing_closure_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<u32>", scope: ![[function_containing_closure_NAMESPACE]]
-// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<u32>", scope: [[function_containing_closure_NAMESPACE]]
+// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<u32>", scope: ![[function_containing_closure_NAMESPACE]]
 
 // generic_async_function<Foo>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[generic_async_function_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[generic_async_function_NAMESPACE]]
 
 // generic_async_function<u32>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<u32>", scope: [[generic_async_function_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}<u32>", scope: ![[generic_async_function_NAMESPACE]]
 
 // generic_async_block<Foo>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[generic_async_block_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[generic_async_block_NAMESPACE]]
 
 // generic_async_block<u32>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<u32>", scope: [[generic_async_block_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{async_block_env#0}<u32>", scope: ![[generic_async_block_NAMESPACE]]
 
 // function_containing_closure<Foo>()
-// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: [[function_containing_closure_NAMESPACE]]
+// NONMSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "{closure_env#0}<debuginfo_generic_closure_env_names::Foo>", scope: ![[function_containing_closure_NAMESPACE]]
-// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<debuginfo_generic_closure_env_names::Foo>", scope: [[function_containing_closure_NAMESPACE]]
+// MSVC: !DICompositeType(tag: DW_TAG_structure_type, name: "closure_env$0<debuginfo_generic_closure_env_names::Foo>", scope: ![[function_containing_closure_NAMESPACE]]
 
 
 #![crate_type = "lib"]
@@ -54,15 +53,14 @@ use std::future::Future;
 pub struct Foo;
 
 pub fn non_generic_closure(x: Foo) -> Box<dyn FnOnce() -> Foo> {
-    // This static only exists to trigger generating the namespace debuginfo for
-    // `function_containing_closure` at a predictable, early point, which makes
-    // writing the FileCheck tests above simpler.
-    static _X: u8 = 0;
     return Box::new(move || x);
 }
 
 fn function_containing_closure<T: 'static>(x: T) -> impl FnOnce() -> T {
-    static _X: u8 = 0; // Same as above
+    // This static only exists to trigger generating the namespace debuginfo for
+    // `function_containing_closure` at a predictable, early point, which makes
+    // writing the FileCheck tests above simpler.
+    static _X: u8 = 0;
 
     return move || x;
 }

src/test/codegen/used_with_arg.rs

@@ -0,0 +1,10 @@
+#![crate_type = "lib"]
+#![feature(used_with_arg)]
+
+// CHECK: @llvm.used = appending global [1 x i8*]{{.*}}USED_LINKER
+#[used(linker)]
+static mut USED_LINKER: [usize; 1] = [0];
+
+// CHECK-NEXT: @llvm.compiler.used = appending global [1 x i8*]{{.*}}USED_COMPILER
+#[used(compiler)]
+static mut USED_COMPILER: [usize; 1] = [0];

src/test/ui/attributes/main-removed-1.rs

@@ -0,0 +1,2 @@
+#[main]  //~ ERROR cannot find attribute `main` in this scope
+fn main() {}

src/test/ui/attributes/main-removed-1.stderr

@@ -0,0 +1,10 @@
+error: cannot find attribute `main` in this scope
+  --> $DIR/main-removed-1.rs:1:3
+   |
+LL | #[main]
+   |   ^^^^
+   |
+   = note: `main` is in scope, but it is a function, not an attribute
+
+error: aborting due to previous error
+

src/test/ui/attributes/main-removed-2/auxiliary/tokyo.rs

@@ -0,0 +1,12 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro_attribute]
+pub fn main(_: TokenStream, input: TokenStream) -> TokenStream {
+    "fn main() { println!(\"Hello Tokyo!\"); }".parse().unwrap()
+}

src/test/ui/attributes/main-removed-2/main.rs

@@ -0,0 +1,11 @@
+// run-pass
+// aux-build:tokyo.rs
+// compile-flags:--extern tokyo
+// edition:2021
+
+use tokyo::main;
+
+#[main]
+fn main() {
+    panic!("the #[main] macro should replace this with non-panicking code")
+}

src/test/ui/attributes/used_with_arg.rs

@@ -0,0 +1,19 @@
+#![feature(used_with_arg)]
+
+#[used(linker)]
+static mut USED_LINKER: [usize; 1] = [0];
+
+#[used(compiler)]
+static mut USED_COMPILER: [usize; 1] = [0];
+
+#[used(compiler)] //~ ERROR `used(compiler)` and `used(linker)` can't be used together
+#[used(linker)]
+static mut USED_COMPILER_LINKER2: [usize; 1] = [0];
+
+#[used(compiler)] //~ ERROR `used(compiler)` and `used(linker)` can't be used together
+#[used(linker)]
+#[used(compiler)]
+#[used(linker)]
+static mut USED_COMPILER_LINKER3: [usize; 1] = [0];
+
+fn main() {}

src/test/ui/attributes/used_with_arg.stderr

@@ -0,0 +1,18 @@
+error: `used(compiler)` and `used(linker)` can't be used together
+  --> $DIR/used_with_arg.rs:9:1
+   |
+LL | #[used(compiler)]
+   | ^^^^^^^^^^^^^^^^^
+LL | #[used(linker)]
+   | ^^^^^^^^^^^^^^^
+
+error: `used(compiler)` and `used(linker)` can't be used together
+  --> $DIR/used_with_arg.rs:13:1
+   |
+LL | #[used(compiler)]
+   | ^^^^^^^^^^^^^^^^^
+LL | #[used(linker)]
+   | ^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+

src/test/ui/attributes/used_with_multi_args.rs

@@ -0,0 +1,6 @@
+#![feature(used_with_arg)]
+
+#[used(compiler, linker)] //~ expected `used`, `used(compiler)` or `used(linker)`
+static mut USED_COMPILER_LINKER: [usize; 1] = [0];
+
+fn main() {}

src/test/ui/attributes/used_with_multi_args.stderr

@@ -0,0 +1,8 @@
+error: expected `used`, `used(compiler)` or `used(linker)`
+  --> $DIR/used_with_multi_args.rs:3:1
+   |
+LL | #[used(compiler, linker)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/feature-gates/feature-gate-used_with_arg.rs

@@ -0,0 +1,7 @@
+#[used(linker)] //~ ERROR `#[used(linker)]` is currently unstable
+static mut USED_LINKER: [usize; 1] = [0];
+
+#[used(compiler)] //~ ERROR `#[used(compiler)]` is currently unstable
+static mut USED_COMPILER: [usize; 1] = [0];
+
+fn main() {}

src/test/ui/feature-gates/feature-gate-used_with_arg.stderr

@@ -0,0 +1,21 @@
+error[E0658]: `#[used(linker)]` is currently unstable
+  --> $DIR/feature-gate-used_with_arg.rs:1:1
+   |
+LL | #[used(linker)]
+   | ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #93798 <https://github.com/rust-lang/rust/issues/93798> for more information
+   = help: add `#![feature(used_with_arg)]` to the crate attributes to enable
+
+error[E0658]: `#[used(compiler)]` is currently unstable
+  --> $DIR/feature-gate-used_with_arg.rs:4:1
+   |
+LL | #[used(compiler)]
+   | ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #93798 <https://github.com/rust-lang/rust/issues/93798> for more information
+   = help: add `#![feature(used_with_arg)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/iterators/collect-into-slice.rs

@@ -0,0 +1,15 @@
+fn process_slice(data: &[i32]) {
+    //~^ NOTE required by a bound in this
+    todo!()
+}
+
+fn main() {
+    let some_generated_vec = (0..10).collect();
+    //~^ ERROR the size for values of type `[i32]` cannot be known at compilation time
+    //~| ERROR a value of type `[i32]` cannot be built since `[i32]` has no definite size
+    //~| NOTE try explicitly collecting into a `Vec<{integer}>`
+    //~| NOTE required by a bound in `collect`
+    //~| NOTE all local variables must have a statically known size
+    //~| NOTE doesn't have a size known at compile-time
+    process_slice(&some_generated_vec);
+}

src/test/ui/iterators/collect-into-slice.stderr

@@ -0,0 +1,26 @@
+error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
+  --> $DIR/collect-into-slice.rs:7:9
+   |
+LL |     let some_generated_vec = (0..10).collect();
+   |         ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[i32]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+
+error[E0277]: a value of type `[i32]` cannot be built since `[i32]` has no definite size
+  --> $DIR/collect-into-slice.rs:7:38
+   |
+LL |     let some_generated_vec = (0..10).collect();
+   |                                      ^^^^^^^ try explicitly collecting into a `Vec<{integer}>`
+   |
+   = help: the trait `FromIterator<{integer}>` is not implemented for `[i32]`
+note: required by a bound in `collect`
+  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
+   |
+LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `collect`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.