Move diagnostic::on_unknown target check

compiler/rustc_attr_parsing/src/attributes/diagnostic/on_unknown.rs

@@ -1,7 +1,11 @@
+use rustc_errors::Diagnostic;
 use rustc_hir::attrs::diagnostic::Directive;
+use rustc_session::lint::builtin::MISPLACED_DIAGNOSTIC_ATTRIBUTES;
 
+use crate::ShouldEmit;
 use crate::attributes::diagnostic::*;
 use crate::attributes::prelude::*;
+use crate::errors::DiagnosticOnUnknownOnlyForImports;
 
 #[derive(Default)]
 pub(crate) struct OnUnknownParser {
@@ -25,6 +29,22 @@ impl OnUnknownParser {
         let span = cx.attr_span;
         self.span = Some(span);
 
+        // At early parsing we get passed `Target::Crate` regardless of the item we're on.
+        // Only do target checking if we're late.
+        let early = matches!(cx.stage.should_emit(), ShouldEmit::Nothing);
+
+        if !early && !matches!(cx.target, Target::Use) {
+            let target_span = cx.target_span;
+            cx.emit_dyn_lint(
+                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                move |dcx, level| {
+                    DiagnosticOnUnknownOnlyForImports { target_span }.into_diag(dcx, level)
+                },
+                span,
+            );
+            return;
+        }
+
         let Some(items) = parse_list(cx, args, mode) else { return };
 
         if let Some(directive) = parse_directive_items(cx, mode, items.mixed(), true) {
@@ -41,7 +61,7 @@ impl<S: Stage> AttributeParser<S> for OnUnknownParser {
             this.parse(cx, args, Mode::DiagnosticOnUnknown);
         },
     )];
-    //FIXME attribute is not parsed for non-use statements but diagnostics are issued in `check_attr.rs`
+    // "Allowed" for all targets, but noop for all but use statements.
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {

compiler/rustc_attr_parsing/src/errors.rs

@@ -267,3 +267,10 @@ pub(crate) struct DiagnosticOnMoveOnlyForAdt;
 #[derive(Diagnostic)]
 #[diag("`#[diagnostic::on_unimplemented]` can only be applied to trait definitions")]
 pub(crate) struct DiagnosticOnUnimplementedOnlyForTraits;
+
+#[derive(Diagnostic)]
+#[diag("`#[diagnostic::on_unknown]` can only be applied to `use` statements")]
+pub(crate) struct DiagnosticOnUnknownOnlyForImports {
+    #[label("not an import")]
+    pub target_span: Span,
+}

compiler/rustc_passes/src/check_attr.rs

@@ -57,13 +57,6 @@ struct DiagnosticOnConstOnlyForNonConstTraitImpls {
     item_span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag("`#[diagnostic::on_unknown]` can only be applied to `use` statements")]
-struct DiagnosticOnUnknownOnlyForImports {
-    #[label("not an import")]
-    item_span: Span,
-}
-
 fn target_from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
     match impl_item.kind {
         hir::ImplItemKind::Const(..) => Target::AssocConst,
@@ -208,7 +201,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 },
                 Attribute::Parsed(AttributeKind::DoNotRecommend{attr_span}) => {self.check_do_not_recommend(*attr_span, hir_id, target, item)},
                 Attribute::Parsed(AttributeKind::OnUnimplemented{directive,..}) => {self.check_diagnostic_on_unimplemented(hir_id, directive.as_deref())},
-                Attribute::Parsed(AttributeKind::OnUnknown { span, .. }) => { self.check_diagnostic_on_unknown(*span, hir_id, target) },
                 Attribute::Parsed(AttributeKind::OnConst{span, ..}) => {self.check_diagnostic_on_const(*span, hir_id, target, item)}
                 Attribute::Parsed(AttributeKind::OnMove { directive , .. }) => {
                     self.check_diagnostic_on_move(hir_id, directive.as_deref())
@@ -260,6 +252,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::NoMain
                     | AttributeKind::NoMangle(..)
                     | AttributeKind::NoStd { .. }
+                    | AttributeKind::OnUnknown { .. }
                     | AttributeKind::Optimize(..)
                     | AttributeKind::PanicRuntime
                     | AttributeKind::PatchableFunctionEntry { .. }
@@ -625,19 +618,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if `#[diagnostic::on_unknown]` is applied to a trait impl
-    fn check_diagnostic_on_unknown(&self, attr_span: Span, hir_id: HirId, target: Target) {
-        if !matches!(target, Target::Use) {
-            let item_span = self.tcx.hir_span(hir_id);
-            self.tcx.emit_node_span_lint(
-                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
-                hir_id,
-                attr_span,
-                DiagnosticOnUnknownOnlyForImports { item_span },
-            );
-        }
-    }
-
     /// Checks if an `#[inline]` is applied to a function or a closure.
     fn check_inline(&self, hir_id: HirId, attr_span: Span, kind: &InlineAttr, target: Target) {
         match target {

tests/ui/diagnostic_namespace/on_unknown/incorrect-locations.stderr

@@ -5,7 +5,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | extern crate std as other_std;
-   | ----------------------------- not an import
+   | ------------------------------ not an import
    |
    = note: `#[warn(misplaced_diagnostic_attributes)]` (part of `#[warn(unknown_or_malformed_diagnostic_attributes)]`) on by default
 
@@ -16,7 +16,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | const CONST: () = ();
-   | --------------- not an import
+   | --------------------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:13:1
@@ -25,7 +25,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | static STATIC: () = ();
-   | ----------------- not an import
+   | ----------------------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:17:1
@@ -34,7 +34,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | type Type = ();
-   | --------- not an import
+   | --------------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:21:1
@@ -43,7 +43,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | enum Enum {}
-   | --------- not an import
+   | ------------ not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:25:1
@@ -52,7 +52,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | impl Enum {}
-   | --------- not an import
+   | ------------ not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:29:1
@@ -70,7 +70,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | fn fun() {}
-   | -------- not an import
+   | ----------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:37:1
@@ -79,7 +79,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | struct Struct {}
-   | ------------- not an import
+   | ---------------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:41:1
@@ -88,7 +88,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | trait Trait {}
-   | ----------- not an import
+   | -------------- not an import
 
 warning: `#[diagnostic::on_unknown]` can only be applied to `use` statements
   --> $DIR/incorrect-locations.rs:45:1
@@ -97,7 +97,7 @@ LL | #[diagnostic::on_unknown(message = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL | impl Trait for i32 {}
-   | ------------------ not an import
+   | --------------------- not an import
 
 warning: 11 warnings emitted