Use attribute name in message for "outer attr used as inner attr" errors

compiler/rustc_attr_parsing/messages.ftl

@@ -86,6 +86,12 @@ attr_parsing_invalid_repr_hint_no_value =
 attr_parsing_invalid_since =
     'since' must be a Rust version number, such as "1.31.0"
 
+attr_parsing_invalid_style = {$is_used_as_inner ->
+        [false] crate-level attribute should be an inner attribute: add an exclamation mark: `#![{$name}]`
+        *[other] the `#![{$name}]` attribute can only be used at the crate root
+    }
+    .note = This attribute does not have an `!`, which means it is applied to this {$target}
+
 attr_parsing_link_ordinal_out_of_range = ordinal value in `link_ordinal` is too large: `{$ordinal}`
     .note = the value may not exceed `u16::MAX`
 

compiler/rustc_attr_parsing/src/attributes/crate_level.rs

@@ -1,3 +1,5 @@
+use rustc_feature::AttributeType;
+
 use super::prelude::*;
 
 pub(crate) struct CrateNameParser;
@@ -7,6 +9,7 @@ impl<S: Stage> SingleAttributeParser<S> for CrateNameParser {
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
     const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
+    const TYPE: AttributeType = AttributeType::CrateLevel;
 
     // FIXME: crate name is allowed on all targets and ignored,
     //        even though it should only be valid on crates of course

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -12,11 +12,15 @@
 //! - [`CombineAttributeParser`](crate::attributes::CombineAttributeParser): makes it easy to implement an attribute which should combine the
 //! contents of attributes, if an attribute appear multiple times in a list
 //!
+//! By default, attributes are allowed anywhere. When adding an attribute that should only be used
+//! at the crate root, consider setting the `TYPE` in the parser trait to
+//! [`AttributeType::CrateLevel`](rustc_feature::AttributeType::CrateLevel).
+//!
 //! Attributes should be added to `crate::context::ATTRIBUTE_PARSERS` to be parsed.
 
 use std::marker::PhantomData;
 
-use rustc_feature::{AttributeTemplate, template};
+use rustc_feature::{AttributeTemplate, AttributeType, template};
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol};
 use thin_vec::ThinVec;
@@ -88,6 +92,8 @@ pub(crate) trait AttributeParser<S: Stage>: Default + 'static {
 
     const ALLOWED_TARGETS: AllowedTargets;
 
+    const TYPE: AttributeType = AttributeType::Normal;
+
     /// The parser has gotten a chance to accept the attributes on an item,
     /// here it can produce an attribute.
     ///
@@ -129,6 +135,8 @@ pub(crate) trait SingleAttributeParser<S: Stage>: 'static {
     /// The template this attribute parser should implement. Used for diagnostics.
     const TEMPLATE: AttributeTemplate;
 
+    const TYPE: AttributeType = AttributeType::Normal;
+
     /// Converts a single syntactical attribute to a single semantic attribute, or [`AttributeKind`]
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind>;
 }
@@ -175,6 +183,8 @@ impl<T: SingleAttributeParser<S>, S: Stage> AttributeParser<S> for Single<T, S>
     )];
     const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
 
+    const TYPE: AttributeType = T::TYPE;
+
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         Some(self.1?.0)
     }
@@ -259,6 +269,7 @@ pub(crate) trait NoArgsAttributeParser<S: Stage>: 'static {
     const PATH: &[Symbol];
     const ON_DUPLICATE: OnDuplicate<S>;
     const ALLOWED_TARGETS: AllowedTargets;
+    const TYPE: AttributeType = AttributeType::Normal;
 
     /// Create the [`AttributeKind`] given attribute's [`Span`].
     const CREATE: fn(Span) -> AttributeKind;
@@ -278,6 +289,7 @@ impl<T: NoArgsAttributeParser<S>, S: Stage> SingleAttributeParser<S> for Without
     const ON_DUPLICATE: OnDuplicate<S> = T::ON_DUPLICATE;
     const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
     const TEMPLATE: AttributeTemplate = template!(Word);
+    const TYPE: AttributeType = T::TYPE;
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         if let Err(span) = args.no_args() {
@@ -311,6 +323,8 @@ pub(crate) trait CombineAttributeParser<S: Stage>: 'static {
     /// The template this attribute parser should implement. Used for diagnostics.
     const TEMPLATE: AttributeTemplate;
 
+    const TYPE: AttributeType = AttributeType::Normal;
+
     /// Converts a single syntactical attribute to a number of elements of the semantic attribute, or [`AttributeKind`]
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
@@ -346,6 +360,7 @@ impl<T: CombineAttributeParser<S>, S: Stage> AttributeParser<S> for Combine<T, S
             group.items.extend(T::extend(cx, args))
         })];
     const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
+    const TYPE: AttributeType = T::TYPE;
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if let Some(first_span) = self.first_span {

compiler/rustc_attr_parsing/src/attributes/traits.rs

@@ -1,5 +1,7 @@
 use std::mem;
 
+use rustc_feature::AttributeType;
+
 use super::prelude::*;
 use crate::attributes::{
     AttributeOrder, NoArgsAttributeParser, OnDuplicate, SingleAttributeParser,
@@ -154,6 +156,7 @@ impl<S: Stage> NoArgsAttributeParser<S> for CoherenceIsCoreParser {
     const PATH: &[Symbol] = &[sym::rustc_coherence_is_core];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
+    const TYPE: AttributeType = AttributeType::CrateLevel;
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::CoherenceIsCore;
 }
 

compiler/rustc_attr_parsing/src/context.rs

@@ -4,12 +4,12 @@ use std::ops::{Deref, DerefMut};
 use std::sync::LazyLock;
 
 use private::Sealed;
-use rustc_ast::{AttrStyle, MetaItemLit, NodeId};
+use rustc_ast::{AttrStyle, CRATE_NODE_ID, MetaItemLit, NodeId};
 use rustc_errors::{Diag, Diagnostic, Level};
-use rustc_feature::AttributeTemplate;
+use rustc_feature::{AttributeTemplate, AttributeType};
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::lints::{AttributeLint, AttributeLintKind};
-use rustc_hir::{AttrPath, HirId};
+use rustc_hir::{AttrPath, CRATE_HIR_ID, HirId};
 use rustc_session::Session;
 use rustc_span::{ErrorGuaranteed, Span, Symbol};
 
@@ -80,6 +80,7 @@ pub(super) struct GroupTypeInnerAccept<S: Stage> {
     pub(super) template: AttributeTemplate,
     pub(super) accept_fn: AcceptFn<S>,
     pub(super) allowed_targets: AllowedTargets,
+    pub(super) attribute_type: AttributeType,
 }
 
 type AcceptFn<S> =
@@ -129,6 +130,7 @@ macro_rules! attribute_parsers {
                                 })
                             }),
                             allowed_targets: <$names as crate::attributes::AttributeParser<$stage>>::ALLOWED_TARGETS,
+                            attribute_type: <$names as crate::attributes::AttributeParser<$stage>>::TYPE,
                         });
                     }
 
@@ -250,6 +252,8 @@ pub trait Stage: Sized + 'static + Sealed {
     ) -> ErrorGuaranteed;
 
     fn should_emit(&self) -> ShouldEmit;
+
+    fn id_is_crate_root(id: Self::Id) -> bool;
 }
 
 // allow because it's a sealed trait
@@ -271,6 +275,10 @@ impl Stage for Early {
     fn should_emit(&self) -> ShouldEmit {
         self.emit_errors
     }
+
+    fn id_is_crate_root(id: Self::Id) -> bool {
+        id == CRATE_NODE_ID
+    }
 }
 
 // allow because it's a sealed trait
@@ -292,6 +300,10 @@ impl Stage for Late {
     fn should_emit(&self) -> ShouldEmit {
         ShouldEmit::ErrorsAndLints
     }
+
+    fn id_is_crate_root(id: Self::Id) -> bool {
+        id == CRATE_HIR_ID
+    }
 }
 
 /// used when parsing attributes for miscellaneous things *before* ast lowering

compiler/rustc_attr_parsing/src/interface.rs

@@ -271,8 +271,8 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
                             };
 
                             (accept.accept_fn)(&mut cx, args);
-
-                            if !matches!(self.stage.should_emit(), ShouldEmit::Nothing) {
+                            if !matches!(cx.stage.should_emit(), ShouldEmit::Nothing) {
+                                Self::check_type(accept.attribute_type, target, &mut cx);
                                 self.check_target(
                                     path.get_attribute_path(),
                                     attr.span,

compiler/rustc_attr_parsing/src/lints.rs

@@ -60,5 +60,19 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<L::Id>, lint_emi
                     attr_span: *span,
                 },
             ),
+
+        &AttributeLintKind::InvalidStyle { ref name, is_used_as_inner, target, target_span } => {
+            lint_emitter.emit_node_span_lint(
+                rustc_session::lint::builtin::UNUSED_ATTRIBUTES,
+                *id,
+                *span,
+                session_diagnostics::InvalidAttrStyle {
+                    name: name.clone(),
+                    is_used_as_inner,
+                    target_span: (!is_used_as_inner).then_some(target_span),
+                    target,
+                },
+            )
+        }
     }
 }

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -6,7 +6,7 @@ use rustc_errors::{
     Applicability, Diag, DiagArgValue, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level,
 };
 use rustc_feature::AttributeTemplate;
-use rustc_hir::AttrPath;
+use rustc_hir::{AttrPath, Target};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
@@ -826,3 +826,13 @@ pub(crate) struct SuffixedLiteralInAttribute {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(LintDiagnostic)]
+#[diag(attr_parsing_invalid_style)]
+pub(crate) struct InvalidAttrStyle {
+    pub name: AttrPath,
+    pub is_used_as_inner: bool,
+    #[note]
+    pub target_span: Option<Span>,
+    pub target: Target,
+}

compiler/rustc_attr_parsing/src/target_checking.rs

@@ -1,13 +1,14 @@
 use std::borrow::Cow;
 
+use rustc_ast::AttrStyle;
 use rustc_errors::DiagArgValue;
-use rustc_feature::Features;
+use rustc_feature::{AttributeType, Features};
 use rustc_hir::lints::{AttributeLint, AttributeLintKind};
 use rustc_hir::{AttrPath, MethodKind, Target};
 use rustc_span::Span;
 
 use crate::AttributeParser;
-use crate::context::Stage;
+use crate::context::{AcceptContext, Stage};
 use crate::session_diagnostics::InvalidTarget;
 
 #[derive(Debug)]
@@ -68,7 +69,7 @@ pub(crate) enum Policy {
     Error(Target),
 }
 
-impl<S: Stage> AttributeParser<'_, S> {
+impl<'sess, S: Stage> AttributeParser<'sess, S> {
     pub(crate) fn check_target(
         &self,
         attr_name: AttrPath,
@@ -111,6 +112,32 @@ impl<S: Stage> AttributeParser<'_, S> {
             }
         }
     }
+
+    pub(crate) fn check_type(
+        attribute_type: AttributeType,
+        target: Target,
+        cx: &mut AcceptContext<'_, 'sess, S>,
+    ) {
+        let is_crate_root = S::id_is_crate_root(cx.target_id);
+
+        if is_crate_root {
+            return;
+        }
+
+        if attribute_type != AttributeType::CrateLevel {
+            return;
+        }
+
+        let lint = AttributeLintKind::InvalidStyle {
+            name: cx.attr_path.clone(),
+            is_used_as_inner: cx.attr_style == AttrStyle::Inner,
+            target,
+            target_span: cx.target_span,
+        };
+        let attr_span = cx.attr_span;
+
+        cx.emit_lint(lint, attr_span);
+    }
 }
 
 /// Takes a list of `allowed_targets` for an attribute, and the `target` the attribute was applied to.

compiler/rustc_hir/src/lints.rs

@@ -35,4 +35,5 @@ pub enum AttributeLintKind {
     IllFormedAttributeInput { suggestions: Vec<String> },
     EmptyAttribute { first_span: Span },
     InvalidTarget { name: AttrPath, target: Target, applied: Vec<String>, only: &'static str },
+    InvalidStyle { name: AttrPath, is_used_as_inner: bool, target: Target, target_span: Span },
 }

compiler/rustc_passes/messages.ftl

@@ -462,8 +462,10 @@ passes_object_lifetime_err =
     {$repr}
 
 passes_outer_crate_level_attr =
-    crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
+    crate-level attribute should be an inner attribute
 
+passes_outer_crate_level_attr_suggestion =
+    add a `!`
 
 passes_panic_unwind_without_std =
     unwinding panics are not supported without std