Auto merge of #88681 - ehuss:duplicate-attributes, r=petrochenkov

Check for duplicate attributes.

This adds some checks for duplicate attributes. In many cases, the duplicates were being ignored without error or warning. This adds several kinds of checks (see `AttributeDuplicates` enum).

The motivation here is to issue unused warnings with similar reasoning for any unused lint, and to error for cases where there are conflicts.

This also adds a check for empty attribute lists in a few attributes where this causes the attribute to be ignored.

Closes #55112.

15 files changed, 1052 insertions, 302 deletions

diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 74a637fde33..f25b2d8f566 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -1,5 +1,6 @@
 //! Built-in attributes and `cfg` flag gating.
 
+use AttributeDuplicates::*;
 use AttributeGate::*;
 use AttributeType::*;
 
@@ -88,11 +89,66 @@ impl AttributeGate {
 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
 #[derive(Clone, Copy, Default)]
 pub struct AttributeTemplate {
+    /// If `true`, the attribute is allowed to be a bare word like `#[test]`.
     pub word: bool,
+    /// If `Some`, the attribute is allowed to take a list of items like `#[allow(..)]`.
     pub list: Option<&'static str>,
+    /// If `Some`, the attribute is allowed to be a name/value pair where the
+    /// value is a string, like `#[must_use = "reason"]`.
     pub name_value_str: Option<&'static str>,
 }
 
+/// How to handle multiple duplicate attributes on the same item.
+#[derive(Clone, Copy, Default)]
+pub enum AttributeDuplicates {
+    /// Duplicates of this attribute are allowed.
+    ///
+    /// This should only be used with attributes where duplicates have semantic
+    /// meaning, or some kind of "additive" behavior. For example, `#[warn(..)]`
+    /// can be specified multiple times, and it combines all the entries. Or use
+    /// this if there is validation done elsewhere.
+    #[default]
+    DuplicatesOk,
+    /// Duplicates after the first attribute will be an unused_attribute warning.
+    ///
+    /// This is usually used for "word" attributes, where they are used as a
+    /// boolean marker, like `#[used]`. It is not necessarily wrong that there
+    /// are duplicates, but the others should probably be removed.
+    WarnFollowing,
+    /// Same as `WarnFollowing`, but only issues warnings for word-style attributes.
+    ///
+    /// This is only for special cases, for example multiple `#[macro_use]` can
+    /// be warned, but multiple `#[macro_use(...)]` should not because the list
+    /// form has different meaning from the word form.
+    WarnFollowingWordOnly,
+    /// Duplicates after the first attribute will be an error.
+    ///
+    /// This should be used where duplicates would be ignored, but carry extra
+    /// meaning that could cause confusion. For example, `#[stable(since="1.0")]
+    /// #[stable(since="2.0")]`, which version should be used for `stable`?
+    ErrorFollowing,
+    /// Duplicates preceding the last instance of the attribute will be an error.
+    ///
+    /// This is the same as `ErrorFollowing`, except the last attribute is the
+    /// one that is "used". This is typically used in cases like codegen
+    /// attributes which usually only honor the last attribute.
+    ErrorPreceding,
+    /// Duplicates after the first attribute will be an unused_attribute warning
+    /// with a note that this will be an error in the future.
+    ///
+    /// This should be used for attributes that should be `ErrorFollowing`, but
+    /// because older versions of rustc silently accepted (and ignored) the
+    /// attributes, this is used to transition.
+    FutureWarnFollowing,
+    /// Duplicates preceding the last instance of the attribute will be a
+    /// warning, with a note that this will be an error in the future.
+    ///
+    /// This is the same as `FutureWarnFollowing`, except the last attribute is
+    /// the one that is "used". Ideally these can eventually migrate to
+    /// `ErrorPreceding`.
+    FutureWarnPreceding,
+}
+
 /// A convenience macro for constructing attribute templates.
 /// E.g., `template!(Word, List: "description")` means that the attribute
 /// supports forms `#[attr]` and `#[attr(description)]`.
@@ -114,36 +170,45 @@ macro_rules! template {
 }
 
 macro_rules! ungated {
-    ($attr:ident, $typ:expr, $tpl:expr $(,)?) => {
-        BuiltinAttribute { name: sym::$attr, type_: $typ, template: $tpl, gate: Ungated }
+    ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(,)?) => {
+        BuiltinAttribute {
+            name: sym::$attr,
+            type_: $typ,
+            template: $tpl,
+            gate: Ungated,
+            duplicates: $duplicates,
+        }
     };
 }
 
 macro_rules! gated {
-    ($attr:ident, $typ:expr, $tpl:expr, $gate:ident, $msg:expr $(,)?) => {
+    ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $gate:ident, $msg:expr $(,)?) => {
         BuiltinAttribute {
             name: sym::$attr,
             type_: $typ,
             template: $tpl,
+            duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)),
         }
     };
-    ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
+    ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $msg:expr $(,)?) => {
         BuiltinAttribute {
             name: sym::$attr,
             type_: $typ,
             template: $tpl,
+            duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)),
         }
     };
 }
 
 macro_rules! rustc_attr {
-    (TEST, $attr:ident, $typ:expr, $tpl:expr $(,)?) => {
+    (TEST, $attr:ident, $typ:expr, $tpl:expr, $duplicate:expr $(,)?) => {
         rustc_attr!(
             $attr,
             $typ,
             $tpl,
+            $duplicate,
             concat!(
                 "the `#[",
                 stringify!($attr),
@@ -152,11 +217,12 @@ macro_rules! rustc_attr {
             ),
         )
     };
-    ($attr:ident, $typ:expr, $tpl:expr, $msg:expr $(,)?) => {
+    ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $msg:expr $(,)?) => {
         BuiltinAttribute {
             name: sym::$attr,
             type_: $typ,
             template: $tpl,
+            duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
         }
     };
@@ -175,6 +241,7 @@ pub struct BuiltinAttribute {
     pub name: Symbol,
     pub type_: AttributeType,
     pub template: AttributeTemplate,
+    pub duplicates: AttributeDuplicates,
     pub gate: AttributeGate,
 }
 
@@ -186,42 +253,48 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     // Conditional compilation:
-    ungated!(cfg, Normal, template!(List: "predicate")),
-    ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ...")),
+    ungated!(cfg, Normal, template!(List: "predicate"), DuplicatesOk),
+    ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), DuplicatesOk),
 
     // Testing:
-    ungated!(ignore, Normal, template!(Word, NameValueStr: "reason")),
+    ungated!(ignore, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing),
     ungated!(
         should_panic, Normal,
-        template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"),
+        template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"), FutureWarnFollowing,
     ),
     // FIXME(Centril): This can be used on stable but shouldn't.
-    ungated!(reexport_test_harness_main, CrateLevel, template!(NameValueStr: "name")),
+    ungated!(reexport_test_harness_main, CrateLevel, template!(NameValueStr: "name"), ErrorFollowing),
 
     // Macros:
-    ungated!(automatically_derived, Normal, template!(Word)),
-    // FIXME(#14407)
-    ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ...")),
-    ungated!(macro_escape, Normal, template!(Word)), // Deprecated synonym for `macro_use`.
-    ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros")),
-    ungated!(proc_macro, Normal, template!(Word)),
+    ungated!(automatically_derived, Normal, template!(Word), WarnFollowing),
+    ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ..."), WarnFollowingWordOnly),
+    ungated!(macro_escape, Normal, template!(Word), WarnFollowing), // Deprecated synonym for `macro_use`.
+    ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros"), WarnFollowing),
+    ungated!(proc_macro, Normal, template!(Word), ErrorFollowing),
     ungated!(
         proc_macro_derive, Normal,
-        template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"),
+        template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
     ),
-    ungated!(proc_macro_attribute, Normal, template!(Word)),
+    ungated!(proc_macro_attribute, Normal, template!(Word), ErrorFollowing),
 
     // Lints:
-    ungated!(warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
-    ungated!(allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
-    ungated!(forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
-    ungated!(deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#)),
-    ungated!(must_use, Normal, template!(Word, NameValueStr: "reason")),
+    ungated!(
+        warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
+    ),
+    ungated!(
+        allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
+    ),
+    ungated!(
+        forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
+    ),
+    ungated!(
+        deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
+    ),
+    ungated!(must_use, Normal, template!(Word, NameValueStr: "reason"), FutureWarnFollowing),
     gated!(
-        must_not_suspend, Normal, template!(Word, NameValueStr: "reason"), must_not_suspend,
-        experimental!(must_not_suspend)
+        must_not_suspend, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing,
+        must_not_suspend, experimental!(must_not_suspend)
     ),
-    // FIXME(#14407)
     ungated!(
         deprecated, Normal,
         template!(
@@ -229,78 +302,86 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
             List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
             NameValueStr: "reason"
         ),
+        // This has special duplicate handling in E0550 to handle duplicates with rustc_deprecated
+        DuplicatesOk
     ),
 
     // Crate properties:
-    ungated!(crate_name, CrateLevel, template!(NameValueStr: "name")),
-    ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|...")),
-    ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored")),
+    ungated!(crate_name, CrateLevel, template!(NameValueStr: "name"), FutureWarnFollowing),
+    ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), FutureWarnFollowing),
+    // crate_id is deprecated
+    ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored"), FutureWarnFollowing),
 
     // ABI, linking, symbols, and FFI
     ungated!(
         link, Normal,
         template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
+        DuplicatesOk,
     ),
-    ungated!(link_name, Normal, template!(NameValueStr: "name")),
-    ungated!(no_link, Normal, template!(Word)),
-    ungated!(repr, Normal, template!(List: "C")),
-    ungated!(export_name, Normal, template!(NameValueStr: "name")),
-    ungated!(link_section, Normal, template!(NameValueStr: "name")),
-    ungated!(no_mangle, Normal, template!(Word)),
-    ungated!(used, Normal, template!(Word)),
+    ungated!(link_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
+    ungated!(no_link, Normal, template!(Word), WarnFollowing),
+    ungated!(repr, Normal, template!(List: "C"), DuplicatesOk),
+    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),
 
     // Limits:
-    ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N")),
-    ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N")),
+    ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
+    ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
     gated!(
-        const_eval_limit, CrateLevel, template!(NameValueStr: "N"), const_eval_limit,
-        experimental!(const_eval_limit)
+        const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
+        const_eval_limit, experimental!(const_eval_limit)
     ),
     gated!(
-        move_size_limit, CrateLevel, template!(NameValueStr: "N"), large_assignments,
-        experimental!(move_size_limit)
+        move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
+        large_assignments, experimental!(move_size_limit)
     ),
 
     // Entry point:
-    ungated!(main, Normal, template!(Word)),
-    ungated!(start, Normal, template!(Word)),
-    ungated!(no_start, CrateLevel, template!(Word)),
-    ungated!(no_main, CrateLevel, template!(Word)),
+    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),
 
     // Modules, prelude, and resolution:
-    ungated!(path, Normal, template!(NameValueStr: "file")),
-    ungated!(no_std, CrateLevel, template!(Word)),
-    ungated!(no_implicit_prelude, Normal, template!(Word)),
-    ungated!(non_exhaustive, Normal, template!(Word)),
+    ungated!(path, Normal, template!(NameValueStr: "file"), FutureWarnFollowing),
+    ungated!(no_std, CrateLevel, template!(Word), WarnFollowing),
+    ungated!(no_implicit_prelude, Normal, template!(Word), WarnFollowing),
+    ungated!(non_exhaustive, Normal, template!(Word), WarnFollowing),
 
     // Runtime
-    ungated!(windows_subsystem, Normal, template!(NameValueStr: "windows|console")),
-    ungated!(panic_handler, Normal, template!(Word)), // RFC 2070
+    ungated!(
+        windows_subsystem, Normal,
+        template!(NameValueStr: "windows|console"), FutureWarnFollowing
+    ),
+    ungated!(panic_handler, Normal, template!(Word), WarnFollowing), // RFC 2070
 
     // Code generation:
-    ungated!(inline, Normal, template!(Word, List: "always|never")),
-    ungated!(cold, Normal, template!(Word)),
-    ungated!(no_builtins, Normal, template!(Word)),
-    ungated!(target_feature, Normal, template!(List: r#"enable = "name""#)),
-    ungated!(track_caller, Normal, template!(Word)),
+    ungated!(inline, Normal, template!(Word, List: "always|never"), FutureWarnFollowing),
+    ungated!(cold, Normal, template!(Word), WarnFollowing),
+    ungated!(no_builtins, Normal, template!(Word), WarnFollowing),
+    ungated!(target_feature, Normal, template!(List: r#"enable = "name""#), DuplicatesOk),
+    ungated!(track_caller, Normal, template!(Word), WarnFollowing),
     gated!(
         no_sanitize, Normal,
-        template!(List: "address, memory, thread"),
+        template!(List: "address, memory, thread"), DuplicatesOk,
         experimental!(no_sanitize)
     ),
-    gated!(no_coverage, Normal, template!(Word), experimental!(no_coverage)),
+    gated!(no_coverage, Normal, template!(Word), WarnFollowing, experimental!(no_coverage)),
 
-    // FIXME: #14408 assume docs are used since rustdoc looks at them.
-    ungated!(doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string")),
+    ungated!(
+        doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string"), DuplicatesOk
+    ),
 
     // ==========================================================================
     // Unstable attributes:
     // ==========================================================================
 
     // Linking:
-    gated!(naked, Normal, template!(Word), naked_functions, experimental!(naked)),
+    gated!(naked, Normal, template!(Word), WarnFollowing, naked_functions, experimental!(naked)),
     gated!(
-        link_ordinal, Normal, template!(List: "ordinal"), raw_dylib,
+        link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, raw_dylib,
         experimental!(link_ordinal)
     ),
 
@@ -309,6 +390,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         name: sym::plugin,
         type_: CrateLevel,
         template: template!(List: "name"),
+        duplicates: DuplicatesOk,
         gate: Gated(
             Stability::Deprecated(
                 "https://github.com/rust-lang/rust/pull/64675",
@@ -321,42 +403,52 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     },
 
     // Testing:
-    gated!(allow_fail, Normal, template!(Word), experimental!(allow_fail)),
+    gated!(allow_fail, Normal, template!(Word), WarnFollowing, experimental!(allow_fail)),
     gated!(
-        test_runner, CrateLevel, template!(List: "path"), custom_test_frameworks,
+        test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
         "custom test frameworks are an unstable feature",
     ),
     // RFC #1268
-    gated!(marker, Normal, template!(Word), marker_trait_attr, experimental!(marker)),
     gated!(
-        thread_local, Normal, template!(Word),
+        marker, Normal, template!(Word), WarnFollowing, marker_trait_attr, experimental!(marker)
+    ),
+    gated!(
+        thread_local, Normal, template!(Word), WarnFollowing,
         "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
     ),
-    gated!(no_core, CrateLevel, template!(Word), experimental!(no_core)),
+    gated!(no_core, CrateLevel, template!(Word), WarnFollowing, experimental!(no_core)),
     // RFC 2412
     gated!(
-        optimize, Normal, template!(List: "size|speed"), optimize_attribute,
+        optimize, Normal, template!(List: "size|speed"), ErrorPreceding, optimize_attribute,
         experimental!(optimize),
     ),
     // RFC 2867
-    gated!(instruction_set, Normal, template!(List: "set"), isa_attribute, experimental!(instruction_set)),
+    gated!(
+        instruction_set, Normal, template!(List: "set"), ErrorPreceding,
+        isa_attribute, experimental!(instruction_set)
+    ),
 
-    gated!(ffi_returns_twice, Normal, template!(Word), experimental!(ffi_returns_twice)),
-    gated!(ffi_pure, Normal, template!(Word), experimental!(ffi_pure)),
-    gated!(ffi_const, Normal, template!(Word), experimental!(ffi_const)),
     gated!(
-        register_attr, CrateLevel, template!(List: "attr1, attr2, ..."),
+        ffi_returns_twice, Normal, template!(Word), WarnFollowing, experimental!(ffi_returns_twice)
+    ),
+    gated!(ffi_pure, Normal, template!(Word), WarnFollowing, experimental!(ffi_pure)),
+    gated!(ffi_const, Normal, template!(Word), WarnFollowing, experimental!(ffi_const)),
+    gated!(
+        register_attr, CrateLevel, template!(List: "attr1, attr2, ..."), DuplicatesOk,
         experimental!(register_attr),
     ),
     gated!(
-        register_tool, CrateLevel, template!(List: "tool1, tool2, ..."),
+        register_tool, CrateLevel, template!(List: "tool1, tool2, ..."), DuplicatesOk,
         experimental!(register_tool),
     ),
 
-    gated!(cmse_nonsecure_entry, Normal, template!(Word), experimental!(cmse_nonsecure_entry)),
+    gated!(
+        cmse_nonsecure_entry, Normal, template!(Word), WarnFollowing,
+        experimental!(cmse_nonsecure_entry)
+    ),
     // RFC 2632
     gated!(
-        default_method_body_is_const, Normal, template!(Word), const_trait_impl,
+        default_method_body_is_const, Normal, template!(Word), WarnFollowing, const_trait_impl,
         "`default_method_body_is_const` is a temporary placeholder for declaring default bodies \
         as `const`, which may be removed or renamed in the future."
     ),
@@ -365,34 +457,33 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Internal attributes: Stability, deprecation, and unsafe:
     // ==========================================================================
 
-    ungated!(feature, CrateLevel, template!(List: "name1, name1, ...")),
-    // FIXME(#14407) -- only looked at on-demand so we can't
-    // guarantee they'll have already been checked.
+    ungated!(feature, CrateLevel, template!(List: "name1, name1, ..."), DuplicatesOk),
+    // DuplicatesOk since it has its own validation
     ungated!(
         rustc_deprecated, Normal,
-        template!(List: r#"since = "version", reason = "...""#)
+        template!(List: r#"since = "version", reason = "...""#), DuplicatesOk // See E0550
+    ),
+    // DuplicatesOk since it has its own validation
+    ungated!(
+        stable, Normal, template!(List: r#"feature = "name", since = "version""#), DuplicatesOk
     ),
-    // FIXME(#14407)
-    ungated!(stable, Normal, template!(List: r#"feature = "name", since = "version""#)),
-    // FIXME(#14407)
     ungated!(
         unstable, Normal,
-        template!(List: r#"feature = "name", reason = "...", issue = "N""#),
+        template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk,
     ),
-    // FIXME(#14407)
-    ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#)),
-    // FIXME(#14407)
-    ungated!(rustc_const_stable, Normal, template!(List: r#"feature = "name""#)),
+    ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
+    ungated!(rustc_const_stable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
     gated!(
-        allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
+        allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
         "allow_internal_unstable side-steps feature gating and stability checks",
     ),
     gated!(
-        rustc_allow_const_fn_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
+        rustc_allow_const_fn_unstable, Normal,
+        template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
     ),
     gated!(
-        allow_internal_unsafe, Normal, template!(Word),
+        allow_internal_unsafe, Normal, template!(Word), WarnFollowing,
         "allow_internal_unsafe side-steps the unsafe_code lint",
     ),
 
@@ -400,9 +491,9 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Internal attributes: Type system related:
     // ==========================================================================
 
-    gated!(fundamental, Normal, template!(Word), experimental!(fundamental)),
+    gated!(fundamental, Normal, template!(Word), WarnFollowing, experimental!(fundamental)),
     gated!(
-        may_dangle, Normal, template!(Word), dropck_eyepatch,
+        may_dangle, Normal, template!(Word), WarnFollowing, dropck_eyepatch,
         "`may_dangle` has unstable semantics and may be removed in the future",
     ),
 
@@ -410,26 +501,32 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Internal attributes: Runtime related:
     // ==========================================================================
 
-    rustc_attr!(rustc_allocator, Normal, template!(Word), IMPL_DETAIL),
-    rustc_attr!(rustc_allocator_nounwind, Normal, template!(Word), IMPL_DETAIL),
-    gated!(alloc_error_handler, Normal, template!(Word), experimental!(alloc_error_handler)),
+    rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
+    rustc_attr!(rustc_allocator_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
+    gated!(
+        alloc_error_handler, Normal, template!(Word), WarnFollowing,
+        experimental!(alloc_error_handler)
+    ),
     gated!(
-        default_lib_allocator, Normal, template!(Word), allocator_internals,
+        default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
         experimental!(default_lib_allocator),
     ),
     gated!(
-        needs_allocator, Normal, template!(Word), allocator_internals,
+        needs_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
         experimental!(needs_allocator),
     ),
-    gated!(panic_runtime, Normal, template!(Word), experimental!(panic_runtime)),
-    gated!(needs_panic_runtime, Normal, template!(Word), experimental!(needs_panic_runtime)),
+    gated!(panic_runtime, Normal, template!(Word), WarnFollowing, experimental!(panic_runtime)),
     gated!(
-        compiler_builtins, Normal, template!(Word),
+        needs_panic_runtime, Normal, template!(Word), WarnFollowing,
+        experimental!(needs_panic_runtime)
+    ),
+    gated!(
+        compiler_builtins, Normal, template!(Word), WarnFollowing,
         "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
         which contains compiler-rt intrinsics and will never be stable",
     ),
     gated!(
-        profiler_runtime, Normal, template!(Word),
+        profiler_runtime, Normal, template!(Word), WarnFollowing,
         "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
         which contains the profiler runtime and will never be stable",
     ),
@@ -439,10 +536,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     gated!(
-        linkage, Normal, template!(NameValueStr: "external|internal|..."),
+        linkage, Normal, template!(NameValueStr: "external|internal|..."), ErrorPreceding,
         "the `linkage` attribute is experimental and not portable across platforms",
     ),
-    rustc_attr!(rustc_std_internal_symbol, Normal, template!(Word), INTERNAL_UNSTABLE),
+    rustc_attr!(
+        rustc_std_internal_symbol, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
+    ),
 
     // ==========================================================================
     // Internal attributes, Macro related:
@@ -450,13 +549,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     rustc_attr!(
         rustc_builtin_macro, Normal,
-        template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"),
+        template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
         IMPL_DETAIL,
     ),
-    rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), INTERNAL_UNSTABLE),
+    rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
     rustc_attr!(
         rustc_macro_transparency, Normal,
-        template!(NameValueStr: "transparent|semitransparent|opaque"),
+        template!(NameValueStr: "transparent|semitransparent|opaque"), ErrorFollowing,
         "used internally for testing macro hygiene",
     ),
 
@@ -470,39 +569,49 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
             List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
             NameValueStr: "message"
         ),
+        ErrorFollowing,
         INTERNAL_UNSTABLE
     ),
     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
-    rustc_attr!(rustc_conversion_suggestion, Normal, template!(Word), INTERNAL_UNSTABLE),
+    rustc_attr!(
+        rustc_conversion_suggestion, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
+    ),
     // Prevents field reads in the marked trait or method to be considered
     // during dead code analysis.
-    rustc_attr!(rustc_trivial_field_reads, Normal, template!(Word), INTERNAL_UNSTABLE),
+    rustc_attr!(
+        rustc_trivial_field_reads, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
+    ),
 
     // ==========================================================================
     // Internal attributes, Const related:
     // ==========================================================================
 
-    rustc_attr!(rustc_promotable, Normal, template!(Word), IMPL_DETAIL),
-    rustc_attr!(rustc_legacy_const_generics, Normal, template!(List: "N"), INTERNAL_UNSTABLE),
+    rustc_attr!(rustc_promotable, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
+    rustc_attr!(
+        rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
+        INTERNAL_UNSTABLE
+    ),
     // Do not const-check this function's body. It will always get replaced during CTFE.
-    rustc_attr!(rustc_do_not_const_check, Normal, template!(Word), INTERNAL_UNSTABLE),
+    rustc_attr!(
+        rustc_do_not_const_check, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
+    ),
 
     // ==========================================================================
     // Internal attributes, Layout related:
     // ==========================================================================
 
     rustc_attr!(
-        rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"),
+        rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing,
         "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
         niche optimizations in libcore and will never be stable",
     ),
     rustc_attr!(
-        rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"),
+        rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing,
         "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
         niche optimizations in libcore and will never be stable",
     ),
     rustc_attr!(
-        rustc_nonnull_optimization_guaranteed, Normal, template!(Word),
+        rustc_nonnull_optimization_guaranteed, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
         niche optimizations in libcore and will never be stable",
     ),
@@ -511,13 +620,14 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Internal attributes, Misc:
     // ==========================================================================
     gated!(
-        lang, Normal, template!(NameValueStr: "name"), lang_items,
+        lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, lang_items,
         "language items are subject to change",
     ),
     BuiltinAttribute {
         name: sym::rustc_diagnostic_item,
         type_: Normal,
         template: template!(NameValueStr: "name"),
+        duplicates: ErrorFollowing,
         gate: Gated(
             Stability::Unstable,
             sym::rustc_attrs,
@@ -527,41 +637,43 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     },
     gated!(
         // Used in resolve:
-        prelude_import, Normal, template!(Word),
+        prelude_import, Normal, template!(Word), WarnFollowing,
         "`#[prelude_import]` is for use by rustc only",
     ),
     gated!(
-        rustc_paren_sugar, Normal, template!(Word), unboxed_closures,
+        rustc_paren_sugar, Normal, template!(Word), WarnFollowing, unboxed_closures,
         "unboxed_closures are still evolving",
     ),
     rustc_attr!(
-        rustc_inherit_overflow_checks, Normal, template!(Word),
+        rustc_inherit_overflow_checks, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
         overflow checking behavior of several libcore functions that are inlined \
         across crates and will never be stable",
     ),
-    rustc_attr!(rustc_reservation_impl, Normal, template!(NameValueStr: "reservation message"),
-                "the `#[rustc_reservation_impl]` attribute is internally used \
-                 for reserving for `for<T> From<!> for T` impl"
+    rustc_attr!(
+        rustc_reservation_impl, Normal,
+        template!(NameValueStr: "reservation message"), ErrorFollowing,
+        "the `#[rustc_reservation_impl]` attribute is internally used \
+         for reserving for `for<T> From<!> for T` impl"
     ),
     rustc_attr!(
-        rustc_test_marker, Normal, template!(Word),
+        rustc_test_marker, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_test_marker]` attribute is used internally to track tests",
     ),
     rustc_attr!(
-        rustc_unsafe_specialization_marker, Normal, template!(Word),
+        rustc_unsafe_specialization_marker, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
     ),
     rustc_attr!(
-        rustc_specialization_trait, Normal, template!(Word),
+        rustc_specialization_trait, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_specialization_trait]` attribute is used to check specializations"
     ),
     rustc_attr!(
-        rustc_main, Normal, template!(Word),
+        rustc_main, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
     ),
     rustc_attr!(
-        rustc_skip_array_during_method_dispatch, Normal, template!(Word),
+        rustc_skip_array_during_method_dispatch, Normal, template!(Word), WarnFollowing,
         "the `#[rustc_skip_array_during_method_dispatch]` attribute is used to exclude a trait \
         from method dispatch when the receiver is an array, for compatibility in editions < 2021."
     ),
@@ -570,48 +682,53 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Internal attributes, Testing:
     // ==========================================================================
 
-    rustc_attr!(TEST, rustc_outlives, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_strict_coherence, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_variance, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ...")),
-    rustc_attr!(TEST, rustc_regions, Normal, template!(Word)),
+    rustc_attr!(TEST, rustc_outlives, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_strict_coherence, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_variance, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ..."), WarnFollowing),
+    rustc_attr!(TEST, rustc_regions, Normal, template!(Word), WarnFollowing),
     rustc_attr!(
         TEST, rustc_error, Normal,
-        template!(Word, List: "delay_span_bug_from_inside_query")
+        template!(Word, List: "delay_span_bug_from_inside_query"), WarnFollowingWordOnly
+    ),
+    rustc_attr!(TEST, rustc_dump_user_substs, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_evaluate_where_clauses, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(
+        TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode"), DuplicatesOk
+    ),
+    rustc_attr!(
+        TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode"), DuplicatesOk
     ),
-    rustc_attr!(TEST, rustc_dump_user_substs, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_evaluate_where_clauses, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode")),
-    rustc_attr!(TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode")),
     rustc_attr!(
         TEST, rustc_clean, Normal,
         template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
+        DuplicatesOk,
     ),
     rustc_attr!(
         TEST, rustc_partition_reused, Normal,
-        template!(List: r#"cfg = "...", module = "...""#),
+        template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
     ),
     rustc_attr!(
         TEST, rustc_partition_codegened, Normal,
-        template!(List: r#"cfg = "...", module = "...""#),
+        template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
     ),
     rustc_attr!(
         TEST, rustc_expected_cgu_reuse, Normal,
-        template!(List: r#"cfg = "...", module = "...", kind = "...""#),
-    ),
-    rustc_attr!(TEST, rustc_symbol_name, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_polymorphize_error, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_def_path, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ...")),
-    rustc_attr!(TEST, rustc_dump_program_clauses, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_dump_env_program_clauses, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_object_lifetime_default, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_dump_vtable, Normal, template!(Word)),
-    rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/)),
+        template!(List: r#"cfg = "...", module = "...", kind = "...""#), DuplicatesOk,
+    ),
+    rustc_attr!(TEST, rustc_symbol_name, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_polymorphize_error, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_def_path, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ..."), DuplicatesOk),
+    rustc_attr!(TEST, rustc_dump_program_clauses, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_dump_env_program_clauses, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_object_lifetime_default, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_dump_vtable, Normal, template!(Word), WarnFollowing),
+    rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/), DuplicatesOk),
     gated!(
-        omit_gdb_pretty_printer_section, Normal, template!(Word),
+        omit_gdb_pretty_printer_section, Normal, template!(Word), WarnFollowing,
         "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
     ),
 ];
diff --git a/compiler/rustc_feature/src/lib.rs b/compiler/rustc_feature/src/lib.rs
index b25aab21e49..bfc537cfae2 100644
--- a/compiler/rustc_feature/src/lib.rs
+++ b/compiler/rustc_feature/src/lib.rs
@@ -11,6 +11,7 @@
 //! even if it is stabilized or removed, *do not remove it*. Instead, move the
 //! symbol to the `accepted` or `removed` modules respectively.
 
+#![feature(derive_default_enum)]
 #![feature(once_cell)]
 
 mod accepted;
@@ -146,6 +147,7 @@ pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZeroU3
 
 pub use accepted::ACCEPTED_FEATURES;
 pub use active::{Features, ACTIVE_FEATURES, INCOMPATIBLE_FEATURES};
+pub use builtin_attrs::AttributeDuplicates;
 pub use builtin_attrs::{
     deprecated_attributes, find_gated_cfg, is_builtin_attr_name, AttributeGate, AttributeTemplate,
     AttributeType, BuiltinAttribute, GatedCfg, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 6ff2259dc5b..2def57cf02a 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -9,9 +9,9 @@ use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
 
 use rustc_ast::{ast, AttrStyle, Attribute, Lit, LitKind, NestedMetaItem};
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, struct_span_err, Applicability};
-use rustc_feature::{AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
+use rustc_feature::{AttributeDuplicates, AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
@@ -23,6 +23,7 @@ use rustc_session::lint::builtin::{
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{MultiSpan, Span, DUMMY_SP};
+use std::collections::hash_map::Entry;
 
 pub(crate) fn target_from_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -69,7 +70,7 @@ impl CheckAttrVisitor<'tcx> {
         let mut doc_aliases = FxHashMap::default();
         let mut is_valid = true;
         let mut specified_inline = None;
-        let mut seen = FxHashSet::default();
+        let mut seen = FxHashMap::default();
         let attrs = self.tcx.hir().attrs(hir_id);
         for attr in attrs {
             let attr_is_valid = match attr.name_or_empty() {
@@ -148,6 +149,8 @@ impl CheckAttrVisitor<'tcx> {
                 _ => {}
             }
 
+            let builtin = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
+
             if hir_id != CRATE_HIR_ID {
                 if let Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) =
                     attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
@@ -165,21 +168,37 @@ impl CheckAttrVisitor<'tcx> {
                 }
             }
 
-            // Duplicate attributes
-            match attr.name_or_empty() {
-                name @ sym::macro_use => {
-                    let args = attr.meta_item_list().unwrap_or_else(Vec::new);
-                    let args: Vec<_> = args.iter().map(|arg| arg.name_or_empty()).collect();
-                    if !seen.insert((name, args)) {
-                        self.tcx.struct_span_lint_hir(
-                            UNUSED_ATTRIBUTES,
-                            hir_id,
+            if let Some(BuiltinAttribute { duplicates, .. }) = builtin {
+                check_duplicates(self.tcx, attr, hir_id, *duplicates, &mut seen);
+            }
+
+            // Warn on useless empty attributes.
+            if matches!(
+                attr.name_or_empty(),
+                sym::macro_use
+                    | sym::allow
+                    | sym::warn
+                    | sym::deny
+                    | sym::forbid
+                    | sym::feature
+                    | sym::repr
+                    | sym::target_feature
+            ) && attr.meta_item_list().map_or(false, |list| list.is_empty())
+            {
+                self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
+                    lint.build("unused attribute")
+                        .span_suggestion(
                             attr.span,
-                            |lint| lint.build("unused attribute").emit(),
-                        );
-                    }
-                }
-                _ => {}
+                            "remove this attribute",
+                            String::new(),
+                            Applicability::MachineApplicable,
+                        )
+                        .note(&format!(
+                            "attribute `{}` with an empty list has no effect",
+                            attr.name_or_empty()
+                        ))
+                        .emit();
+                });
             }
         }
 
@@ -1990,3 +2009,77 @@ fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers { check_mod_attrs, ..*providers };
 }
+
+fn check_duplicates(
+    tcx: TyCtxt<'_>,
+    attr: &Attribute,
+    hir_id: HirId,
+    duplicates: AttributeDuplicates,
+    seen: &mut FxHashMap<Symbol, Span>,
+) {
+    use AttributeDuplicates::*;
+    if matches!(duplicates, WarnFollowingWordOnly) && !attr.is_word() {
+        return;
+    }
+    match duplicates {
+        DuplicatesOk => {}
+        WarnFollowing | FutureWarnFollowing | WarnFollowingWordOnly | FutureWarnPreceding => {
+            match seen.entry(attr.name_or_empty()) {
+                Entry::Occupied(mut entry) => {
+                    let (this, other) = if matches!(duplicates, FutureWarnPreceding) {
+                        let to_remove = entry.insert(attr.span);
+                        (to_remove, attr.span)
+                    } else {
+                        (attr.span, *entry.get())
+                    };
+                    tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, this, |lint| {
+                        let mut db = lint.build("unused attribute");
+                        db.span_note(other, "attribute also specified here").span_suggestion(
+                            this,
+                            "remove this attribute",
+                            String::new(),
+                            Applicability::MachineApplicable,
+                        );
+                        if matches!(duplicates, FutureWarnFollowing | FutureWarnPreceding) {
+                            db.warn(
+                                "this was previously accepted by the compiler but is \
+                                 being phased out; it will become a hard error in \
+                                 a future release!",
+                            );
+                        }
+                        db.emit();
+                    });
+                }
+                Entry::Vacant(entry) => {
+                    entry.insert(attr.span);
+                }
+            }
+        }
+        ErrorFollowing | ErrorPreceding => match seen.entry(attr.name_or_empty()) {
+            Entry::Occupied(mut entry) => {
+                let (this, other) = if matches!(duplicates, ErrorPreceding) {
+                    let to_remove = entry.insert(attr.span);
+                    (to_remove, attr.span)
+                } else {
+                    (attr.span, *entry.get())
+                };
+                tcx.sess
+                    .struct_span_err(
+                        this,
+                        &format!("multiple `{}` attributes", attr.name_or_empty()),
+                    )
+                    .span_note(other, "attribute also specified here")
+                    .span_suggestion(
+                        this,
+                        "remove this attribute",
+                        String::new(),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(attr.span);
+            }
+        },
+    }
+}
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 498c9f7c64e..b9db8a6be59 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -2861,14 +2861,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         } else if attr.has_name(sym::link_name) {
             codegen_fn_attrs.link_name = attr.value_str();
         } else if attr.has_name(sym::link_ordinal) {
-            if link_ordinal_span.is_some() {
-                tcx.sess
-                    .struct_span_err(
-                        attr.span,
-                        "multiple `link_ordinal` attributes on a single definition",
-                    )
-                    .emit();
-            }
             link_ordinal_span = Some(attr.span);
             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
                 codegen_fn_attrs.link_ordinal = ordinal;
diff --git a/src/test/ui/empty/empty-attributes.rs b/src/test/ui/empty/empty-attributes.rs
new file mode 100644
index 00000000000..7e9b05587b0
--- /dev/null
+++ b/src/test/ui/empty/empty-attributes.rs
@@ -0,0 +1,14 @@
+#![deny(unused_attributes)]
+#![allow()] //~ ERROR unused attribute
+#![warn()] //~ ERROR unused attribute
+#![deny()] //~ ERROR unused attribute
+#![forbid()] //~ ERROR unused attribute
+#![feature()] //~ ERROR unused attribute
+
+#[repr()] //~ ERROR unused attribute
+pub struct S;
+
+#[target_feature()] //~ ERROR unused attribute
+pub unsafe fn foo() {}
+
+fn main() {}
diff --git a/src/test/ui/empty/empty-attributes.stderr b/src/test/ui/empty/empty-attributes.stderr
new file mode 100644
index 00000000000..e0798e4f0c6
--- /dev/null
+++ b/src/test/ui/empty/empty-attributes.stderr
@@ -0,0 +1,63 @@
+error: unused attribute
+  --> $DIR/empty-attributes.rs:8:1
+   |
+LL | #[repr()]
+   | ^^^^^^^^^ help: remove this attribute
+   |
+note: the lint level is defined here
+  --> $DIR/empty-attributes.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+   = note: attribute `repr` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:11:1
+   |
+LL | #[target_feature()]
+   | ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `target_feature` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:2:1
+   |
+LL | #![allow()]
+   | ^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `allow` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:3:1
+   |
+LL | #![warn()]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `warn` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:4:1
+   |
+LL | #![deny()]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `deny` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:5:1
+   |
+LL | #![forbid()]
+   | ^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `forbid` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:6:1
+   |
+LL | #![feature()]
+   | ^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `feature` with an empty list has no effect
+
+error: aborting due to 7 previous errors
+
diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.rs b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.rs
index 44abe160f87..1fe133ac2bc 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.rs
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.rs
@@ -134,4 +134,27 @@ mod start {
     //~^ ERROR: `start` attribute can only be used on functions
 }
 
+#[repr(C)]
+//~^ ERROR: attribute should be applied to a struct, enum, or union
+mod repr {
+//~^ NOTE not a struct, enum, or union
+    mod inner { #![repr(C)] }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    #[repr(C)] fn f() { }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    struct S;
+
+    #[repr(C)] type T = S;
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    #[repr(C)] impl S { }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+}
+
 fn main() {}
diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.stderr b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.stderr
index aed1312155d..9e2e2d4137d 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.stderr
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.stderr
@@ -91,6 +91,21 @@ LL | |     }
 LL | | }
    | |_- not a free function, impl method or static
 
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:137:8
+   |
+LL |   #[repr(C)]
+   |          ^
+LL |
+LL | / mod repr {
+LL | |
+LL | |     mod inner { #![repr(C)] }
+LL | |
+...  |
+LL | |
+LL | | }
+   | |_- not a struct, enum, or union
+
 error: attribute should be applied to an `extern crate` item
   --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:25:1
    |
@@ -235,7 +250,31 @@ error: attribute should be applied to a free function, impl method or static
 LL |         #[export_name = "2200"] fn bar() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^ ----------- not a free function, impl method or static
 
-error: aborting due to 34 previous errors
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:141:25
+   |
+LL |     mod inner { #![repr(C)] }
+   |     --------------------^---- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:145:12
+   |
+LL |     #[repr(C)] fn f() { }
+   |            ^   ---------- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:151:12
+   |
+LL |     #[repr(C)] type T = S;
+   |            ^   ----------- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:155:12
+   |
+LL |     #[repr(C)] impl S { }
+   |            ^   ---------- not a struct, enum, or union
+
+error: aborting due to 39 previous errors
 
-Some errors have detailed explanations: E0518, E0658.
-For more information about an error, try `rustc --explain E0518`.
+Some errors have detailed explanations: E0517, E0518, E0658.
+For more information about an error, try `rustc --explain E0517`.
diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
index 97fa775967d..1ddf8508cc8 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
@@ -245,19 +245,6 @@ mod bench {
     impl S { }
 }
 
-#[repr()]
-mod repr {
-    mod inner { #![repr()] }
-
-    #[repr()] fn f() { }
-
-    struct S;
-
-    #[repr()] type T = S;
-
-    #[repr()] impl S { }
-}
-
 #[path = "3800"]
 mod path {
     mod inner { #![path="3800"] }
diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
index 214584f47e9..b98374bfa80 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
@@ -173,7 +173,7 @@ LL |     #[deny(x5100)] impl S { }
    |            ^^^^^
 
 warning: `#[macro_escape]` is a deprecated synonym for `#[macro_use]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:412:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:399:17
    |
 LL |     mod inner { #![macro_escape] }
    |                 ^^^^^^^^^^^^^^^^
@@ -181,7 +181,7 @@ LL |     mod inner { #![macro_escape] }
    = help: try an outer attribute: `#[macro_use]`
 
 warning: `#[macro_escape]` is a deprecated synonym for `#[macro_use]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:409:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:396:1
    |
 LL | #[macro_escape]
    | ^^^^^^^^^^^^^^^
@@ -213,13 +213,13 @@ LL | #![warn(unused_attributes, unknown_lints)]
    |         ^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:278:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:265:1
    |
 LL | #[automatically_derived]
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:296:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:283:1
    |
 LL |   #[no_mangle]
    |   ^^^^^^^^^^^^
@@ -236,31 +236,31 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:336:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:323:1
    |
 LL | #[should_panic]
    | ^^^^^^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:354:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:341:1
    |
 LL | #[ignore]
    | ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:389:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:376:1
    |
 LL | #[reexport_test_harness_main = "2900"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:429:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:416:1
    |
 LL | #[no_std]
    | ^^^^^^^^^
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:465:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:452:1
    |
 LL |   #[cold]
    |   ^^^^^^^
@@ -277,7 +277,7 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:494:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:481:1
    |
 LL |   #[link_name = "1900"]
    |   ^^^^^^^^^^^^^^^^^^^^^
@@ -294,7 +294,7 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:533:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:520:1
    |
 LL |   #[link_section = "1800"]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -311,37 +311,37 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:624:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:611:1
    |
 LL | #[crate_name = "0900"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:643:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:630:1
    |
 LL | #[crate_type = "0800"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:662:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:649:1
    |
 LL | #[feature(x0600)]
    | ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:682:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:669:1
    |
 LL | #[no_main]
    | ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:714:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:701:1
    |
 LL | #[recursion_limit="0200"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:733:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:720:1
    |
 LL | #[type_length_limit="0100"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -443,55 +443,55 @@ LL |     #[macro_export] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:265:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:252:5
    |
 LL |     #[path = "3800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:268:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:255:5
    |
 LL |     #[path = "3800"]  struct S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:271:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:258:5
    |
 LL |     #[path = "3800"] type T = S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:274:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:261:5
    |
 LL |     #[path = "3800"] impl S { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:281:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:268:17
    |
 LL |     mod inner { #![automatically_derived] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:284:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:271:5
    |
 LL |     #[automatically_derived] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:287:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:274:5
    |
 LL |     #[automatically_derived] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:290:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:277:5
    |
 LL |     #[automatically_derived] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:301:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:288:17
    |
 LL |     mod inner { #![no_mangle] }
    |     ------------^^^^^^^^^^^^^-- not a free function, impl method or static
@@ -499,7 +499,7 @@ LL |     mod inner { #![no_mangle] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:308:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:295:5
    |
 LL |     #[no_mangle] struct S;
    |     ^^^^^^^^^^^^ --------- not a free function, impl method or static
@@ -507,7 +507,7 @@ LL |     #[no_mangle] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:313:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:300:5
    |
 LL |     #[no_mangle] type T = S;
    |     ^^^^^^^^^^^^ ----------- not a free function, impl method or static
@@ -515,7 +515,7 @@ LL |     #[no_mangle] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:318:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:305:5
    |
 LL |     #[no_mangle] impl S { }
    |     ^^^^^^^^^^^^ ---------- not a free function, impl method or static
@@ -523,7 +523,7 @@ LL |     #[no_mangle] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:324:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:311:9
    |
 LL |         #[no_mangle] fn foo();
    |         ^^^^^^^^^^^^ --------- not a free function, impl method or static
@@ -531,7 +531,7 @@ LL |         #[no_mangle] fn foo();
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:329:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:316:9
    |
 LL |         #[no_mangle] fn bar() {}
    |         ^^^^^^^^^^^^ ----------- not a free function, impl method or static
@@ -539,163 +539,163 @@ LL |         #[no_mangle] fn bar() {}
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:339:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:326:17
    |
 LL |     mod inner { #![should_panic] }
    |                 ^^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:344:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:331:5
    |
 LL |     #[should_panic] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:347:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:334:5
    |
 LL |     #[should_panic] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:350:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:337:5
    |
 LL |     #[should_panic] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:357:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:344:17
    |
 LL |     mod inner { #![ignore] }
    |                 ^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:362:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:349:5
    |
 LL |     #[ignore] struct S;
    |     ^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:365:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:352:5
    |
 LL |     #[ignore] type T = S;
    |     ^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:368:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:355:5
    |
 LL |     #[ignore] impl S { }
    |     ^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:376:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:363:5
    |
 LL |     #[no_implicit_prelude] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:379:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:366:5
    |
 LL |     #[no_implicit_prelude] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:382:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:369:5
    |
 LL |     #[no_implicit_prelude] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:385:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:372:5
    |
 LL |     #[no_implicit_prelude] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:392:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:379:17
    |
 LL |     mod inner { #![reexport_test_harness_main="2900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:395:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:382:5
    |
 LL |     #[reexport_test_harness_main = "2900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:398:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:385:5
    |
 LL |     #[reexport_test_harness_main = "2900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:401:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:388:5
    |
 LL |     #[reexport_test_harness_main = "2900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:404:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:391:5
    |
 LL |     #[reexport_test_harness_main = "2900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:416:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:403:5
    |
 LL |     #[macro_escape] fn f() { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:419:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:406:5
    |
 LL |     #[macro_escape] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:422:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:409:5
    |
 LL |     #[macro_escape] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:425:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:412:5
    |
 LL |     #[macro_escape] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:432:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:419:17
    |
 LL |     mod inner { #![no_std] }
    |                 ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:435:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:422:5
    |
 LL |     #[no_std] fn f() { }
    |     ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:438:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:425:5
    |
 LL |     #[no_std] struct S;
    |     ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:441:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:428:5
    |
 LL |     #[no_std] type T = S;
    |     ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:444:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:431:5
    |
 LL |     #[no_std] impl S { }
    |     ^^^^^^^^^
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:471:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:458:17
    |
 LL |     mod inner { #![cold] }
    |     ------------^^^^^^^^-- not a function
@@ -703,7 +703,7 @@ LL |     mod inner { #![cold] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:478:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:465:5
    |
 LL |     #[cold] struct S;
    |     ^^^^^^^ --------- not a function
@@ -711,7 +711,7 @@ LL |     #[cold] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:483:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:470:5
    |
 LL |     #[cold] type T = S;
    |     ^^^^^^^ ----------- not a function
@@ -719,7 +719,7 @@ LL |     #[cold] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:488:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:475:5
    |
 LL |     #[cold] impl S { }
    |     ^^^^^^^ ---------- not a function
@@ -727,7 +727,7 @@ LL |     #[cold] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:500:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:487:5
    |
 LL |     #[link_name = "1900"]
    |     ^^^^^^^^^^^^^^^^^^^^^
@@ -737,13 +737,13 @@ LL |     extern "C" { }
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 help: try `#[link(name = "1900")]` instead
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:500:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:487:5
    |
 LL |     #[link_name = "1900"]
    |     ^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:507:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:494:17
    |
 LL |     mod inner { #![link_name="1900"] }
    |     ------------^^^^^^^^^^^^^^^^^^^^-- not a foreign function or static
@@ -751,7 +751,7 @@ LL |     mod inner { #![link_name="1900"] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:512:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:499:5
    |
 LL |     #[link_name = "1900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^ ---------- not a foreign function or static
@@ -759,7 +759,7 @@ LL |     #[link_name = "1900"] fn f() { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:517:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:504:5
    |
 LL |     #[link_name = "1900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^ --------- not a foreign function or static
@@ -767,7 +767,7 @@ LL |     #[link_name = "1900"] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:522:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:509:5
    |
 LL |     #[link_name = "1900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^ ----------- not a foreign function or static
@@ -775,7 +775,7 @@ LL |     #[link_name = "1900"] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:527:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:514:5
    |
 LL |     #[link_name = "1900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^ ---------- not a foreign function or static
@@ -783,7 +783,7 @@ LL |     #[link_name = "1900"] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:539:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:526:17
    |
 LL |     mod inner { #![link_section="1800"] }
    |     ------------^^^^^^^^^^^^^^^^^^^^^^^-- not a function or static
@@ -791,7 +791,7 @@ LL |     mod inner { #![link_section="1800"] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:546:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:533:5
    |
 LL |     #[link_section = "1800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ --------- not a function or static
@@ -799,7 +799,7 @@ LL |     #[link_section = "1800"] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:551:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:538:5
    |
 LL |     #[link_section = "1800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ ----------- not a function or static
@@ -807,7 +807,7 @@ LL |     #[link_section = "1800"] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:556:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:543:5
    |
 LL |     #[link_section = "1800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ ---------- not a function or static
@@ -815,181 +815,181 @@ LL |     #[link_section = "1800"] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:627:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:614:17
    |
 LL |     mod inner { #![crate_name="0900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:630:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:617:5
    |
 LL |     #[crate_name = "0900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:633:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:620:5
    |
 LL |     #[crate_name = "0900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:636:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:623:5
    |
 LL |     #[crate_name = "0900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:639:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:626:5
    |
 LL |     #[crate_name = "0900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:646:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:633:17
    |
 LL |     mod inner { #![crate_type="0800"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:649:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:636:5
    |
 LL |     #[crate_type = "0800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:652:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:639:5
    |
 LL |     #[crate_type = "0800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:655:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:642:5
    |
 LL |     #[crate_type = "0800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:658:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:645:5
    |
 LL |     #[crate_type = "0800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:665:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:652:17
    |
 LL |     mod inner { #![feature(x0600)] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:668:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:655:5
    |
 LL |     #[feature(x0600)] fn f() { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:671:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:658:5
    |
 LL |     #[feature(x0600)] struct S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:674:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:661:5
    |
 LL |     #[feature(x0600)] type T = S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:677:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:664:5
    |
 LL |     #[feature(x0600)] impl S { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:685:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:672:17
    |
 LL |     mod inner { #![no_main] }
    |                 ^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:688:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:675:5
    |
 LL |     #[no_main] fn f() { }
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:691:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:678:5
    |
 LL |     #[no_main] struct S;
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:694:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:681:5
    |
 LL |     #[no_main] type T = S;
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:697:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:684:5
    |
 LL |     #[no_main] impl S { }
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:717:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:704:17
    |
 LL |     mod inner { #![recursion_limit="0200"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:720:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:707:5
    |
 LL |     #[recursion_limit="0200"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:723:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:710:5
    |
 LL |     #[recursion_limit="0200"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:726:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:713:5
    |
 LL |     #[recursion_limit="0200"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:729:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:716:5
    |
 LL |     #[recursion_limit="0200"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:736:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:723:17
    |
 LL |     mod inner { #![type_length_limit="0100"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:739:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:726:5
    |
 LL |     #[type_length_limit="0100"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:742:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:729:5
    |
 LL |     #[type_length_limit="0100"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:745:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:732:5
    |
 LL |     #[type_length_limit="0100"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:748:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:735:5
    |
 LL |     #[type_length_limit="0100"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/src/test/ui/lint/unused/unused-attr-duplicate.rs b/src/test/ui/lint/unused/unused-attr-duplicate.rs
new file mode 100644
index 00000000000..074d5a92ad6
--- /dev/null
+++ b/src/test/ui/lint/unused/unused-attr-duplicate.rs
@@ -0,0 +1,108 @@
+// Tests for repeating attribute warnings.
+// aux-build:lint_unused_extern_crate.rs
+// compile-flags:--test
+// Not tested due to extra requirements:
+// - panic_handler: needs extra setup
+// - target_feature: platform-specific
+// - link_section: platform-specific
+// - proc_macro, proc_macro_derive, proc_macro_attribute: needs to be a
+//   proc-macro, and have special handling for mixing.
+// - unstable attributes (not going to bother)
+// - no_main: extra setup
+#![deny(unused_attributes)]
+#![crate_name = "unused_attr_duplicate"]
+#![crate_name = "unused_attr_duplicate2"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#![crate_type = "bin"]
+#![crate_type = "rlib"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#![recursion_limit = "128"]
+#![recursion_limit = "256"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#![type_length_limit = "1048576"]
+#![type_length_limit = "1"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#![no_std]
+#![no_std] //~ ERROR unused attribute
+#![no_implicit_prelude]
+#![no_implicit_prelude] //~ ERROR unused attribute
+#![windows_subsystem = "console"]
+#![windows_subsystem = "windows"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#![no_builtins]
+#![no_builtins] //~ ERROR unused attribute
+
+#[no_link]
+#[no_link] //~ ERROR unused attribute
+extern crate lint_unused_extern_crate;
+
+#[macro_use]
+#[macro_use] //~ ERROR unused attribute
+pub mod m {
+    #[macro_export]
+    #[macro_export] //~ ERROR unused attribute
+    macro_rules! foo {
+        () => {};
+    }
+}
+
+#[path = "auxiliary/lint_unused_extern_crate.rs"]
+#[path = "bar.rs"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+pub mod from_path;
+
+#[test]
+#[ignore]
+#[ignore = "some text"] //~ ERROR unused attribute
+#[should_panic]
+#[should_panic(expected = "values don't match")] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+fn t1() {}
+
+#[must_use]
+#[must_use = "some message"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+// No warnings for #[repr], would require more logic.
+#[repr(C)]
+#[repr(C)]
+#[non_exhaustive]
+#[non_exhaustive] //~ ERROR unused attribute
+pub struct X;
+
+#[automatically_derived]
+#[automatically_derived] //~ ERROR unused attribute
+impl X {}
+
+#[inline(always)]
+#[inline(never)] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#[cold]
+#[cold] //~ ERROR unused attribute
+#[track_caller]
+#[track_caller] //~ ERROR unused attribute
+pub fn xyz() {}
+
+// No warnings for #[link], would require more logic.
+#[link(name = "rust_test_helpers", kind = "static")]
+#[link(name = "rust_test_helpers", kind = "static")]
+extern "C" {
+    #[link_name = "this_does_not_exist"] //~ ERROR unused attribute
+    //~^ WARN this was previously accepted
+    #[link_name = "rust_dbg_extern_identity_u32"]
+    pub fn name_in_rust(v: u32) -> u32;
+}
+
+#[export_name = "exported_symbol_name"] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
+#[export_name = "exported_symbol_name2"]
+pub fn export_test() {}
+
+#[no_mangle]
+#[no_mangle] //~ ERROR unused attribute
+pub fn no_mangle_test() {}
+
+#[used]
+#[used] //~ ERROR unused attribute
+static FOO: u32 = 0;
+
+fn main() {}
diff --git a/src/test/ui/lint/unused/unused-attr-duplicate.stderr b/src/test/ui/lint/unused/unused-attr-duplicate.stderr
new file mode 100644
index 00000000000..d4305add0aa
--- /dev/null
+++ b/src/test/ui/lint/unused/unused-attr-duplicate.stderr
@@ -0,0 +1,306 @@
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:36:1
+   |
+LL | #[no_link]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+note: the lint level is defined here
+  --> $DIR/unused-attr-duplicate.rs:12:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:35:1
+   |
+LL | #[no_link]
+   | ^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:40:1
+   |
+LL | #[macro_use]
+   | ^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:39:1
+   |
+LL | #[macro_use]
+   | ^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:50:1
+   |
+LL | #[path = "bar.rs"]
+   | ^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:49:1
+   |
+LL | #[path = "auxiliary/lint_unused_extern_crate.rs"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:56:1
+   |
+LL | #[ignore = "some text"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:55:1
+   |
+LL | #[ignore]
+   | ^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:58:1
+   |
+LL | #[should_panic(expected = "values don't match")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:57:1
+   |
+LL | #[should_panic]
+   | ^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:63:1
+   |
+LL | #[must_use = "some message"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:62:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:69:1
+   |
+LL | #[non_exhaustive]
+   | ^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:68:1
+   |
+LL | #[non_exhaustive]
+   | ^^^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:73:1
+   |
+LL | #[automatically_derived]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:72:1
+   |
+LL | #[automatically_derived]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:77:1
+   |
+LL | #[inline(never)]
+   | ^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:76:1
+   |
+LL | #[inline(always)]
+   | ^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:80:1
+   |
+LL | #[cold]
+   | ^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:79:1
+   |
+LL | #[cold]
+   | ^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:82:1
+   |
+LL | #[track_caller]
+   | ^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:81:1
+   |
+LL | #[track_caller]
+   | ^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:95:1
+   |
+LL | #[export_name = "exported_symbol_name"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:97:1
+   |
+LL | #[export_name = "exported_symbol_name2"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:101:1
+   |
+LL | #[no_mangle]
+   | ^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:100:1
+   |
+LL | #[no_mangle]
+   | ^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:105:1
+   |
+LL | #[used]
+   | ^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:104:1
+   |
+LL | #[used]
+   | ^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:89:5
+   |
+LL |     #[link_name = "this_does_not_exist"]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:91:5
+   |
+LL |     #[link_name = "rust_dbg_extern_identity_u32"]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:14:1
+   |
+LL | #![crate_name = "unused_attr_duplicate2"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:13:1
+   |
+LL | #![crate_name = "unused_attr_duplicate"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:17:1
+   |
+LL | #![crate_type = "rlib"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:16:1
+   |
+LL | #![crate_type = "bin"]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:20:1
+   |
+LL | #![recursion_limit = "256"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:19:1
+   |
+LL | #![recursion_limit = "128"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:23:1
+   |
+LL | #![type_length_limit = "1"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:22:1
+   |
+LL | #![type_length_limit = "1048576"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:26:1
+   |
+LL | #![no_std]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:25:1
+   |
+LL | #![no_std]
+   | ^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:28:1
+   |
+LL | #![no_implicit_prelude]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:27:1
+   |
+LL | #![no_implicit_prelude]
+   | ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:30:1
+   |
+LL | #![windows_subsystem = "windows"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:29:1
+   |
+LL | #![windows_subsystem = "console"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:33:1
+   |
+LL | #![no_builtins]
+   | ^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:32:1
+   |
+LL | #![no_builtins]
+   | ^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-duplicate.rs:43:5
+   |
+LL |     #[macro_export]
+   |     ^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unused-attr-duplicate.rs:42:5
+   |
+LL |     #[macro_export]
+   |     ^^^^^^^^^^^^^^^
+
+error: aborting due to 24 previous errors
+
diff --git a/src/test/ui/macros/macro-use-all-and-none.stderr b/src/test/ui/macros/macro-use-all-and-none.stderr
index bdee5f4d872..6de7ffb2f63 100644
--- a/src/test/ui/macros/macro-use-all-and-none.stderr
+++ b/src/test/ui/macros/macro-use-all-and-none.stderr
@@ -2,13 +2,14 @@ warning: unused attribute
   --> $DIR/macro-use-all-and-none.rs:7:1
    |
 LL | #[macro_use()]
-   | ^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: the lint level is defined here
   --> $DIR/macro-use-all-and-none.rs:4:9
    |
 LL | #![warn(unused_attributes)]
    |         ^^^^^^^^^^^^^^^^^
+   = note: attribute `macro_use` with an empty list has no effect
 
 warning: 1 warning emitted
 
diff --git a/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.rs b/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.rs
index 98741212677..0ab994ecd45 100644
--- a/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.rs
+++ b/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.rs
@@ -4,9 +4,8 @@
 
 #[link(name = "foo", kind = "raw-dylib")]
 extern "C" {
-    #[link_ordinal(1)]
+    #[link_ordinal(1)] //~ ERROR multiple `link_ordinal` attributes
     #[link_ordinal(2)]
-    //~^ ERROR multiple `link_ordinal` attributes on a single definition
     fn foo();
 }
 
diff --git a/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.stderr b/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.stderr
index a79fb2de944..4772533ab2f 100644
--- a/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.stderr
+++ b/src/test/ui/rfc-2627-raw-dylib/link-ordinal-multiple.stderr
@@ -7,7 +7,13 @@ LL | #![feature(raw_dylib)]
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #58713 <https://github.com/rust-lang/rust/issues/58713> for more information
 
-error: multiple `link_ordinal` attributes on a single definition
+error: multiple `link_ordinal` attributes
+  --> $DIR/link-ordinal-multiple.rs:7:5
+   |
+LL |     #[link_ordinal(1)]
+   |     ^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
   --> $DIR/link-ordinal-multiple.rs:8:5
    |
 LL |     #[link_ordinal(2)]