Rollup of 6 pull requests

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

@@ -1,19 +1,25 @@
+use rustc_errors::Diagnostic;
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::lints::AttributeLintKind;
-use rustc_session::lint::builtin::MALFORMED_DIAGNOSTIC_ATTRIBUTES;
+use rustc_session::lint::builtin::{
+    MALFORMED_DIAGNOSTIC_ATTRIBUTES, MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+};
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{OnDuplicate, SingleAttributeParser};
 use crate::context::{AcceptContext, Stage};
+use crate::errors::IncorrectDoNotRecommendLocation;
 use crate::parser::ArgParser;
 use crate::target_checking::{ALL_TARGETS, AllowedTargets};
 
 pub(crate) struct DoNotRecommendParser;
 impl<S: Stage> SingleAttributeParser<S> for DoNotRecommendParser {
     const PATH: &[Symbol] = &[sym::diagnostic, sym::do_not_recommend];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
-    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); // Checked in check_attr.
+    // "Allowed" on any target, noop on all but trait impls
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
     const TEMPLATE: AttributeTemplate = template!(Word /*doesn't matter */);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser) -> Option<AttributeKind> {
@@ -25,6 +31,19 @@ impl<S: Stage> SingleAttributeParser<S> for DoNotRecommendParser {
                 attr_span,
             );
         }
+
+        if !matches!(cx.target, Target::Impl { of_trait: true }) {
+            let target_span = cx.target_span;
+            cx.emit_dyn_lint(
+                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                move |dcx, level| {
+                    IncorrectDoNotRecommendLocation { target_span }.into_diag(dcx, level)
+                },
+                attr_span,
+            );
+            return None;
+        }
+
         Some(AttributeKind::DoNotRecommend { attr_span })
     }
 }

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

@@ -1,8 +1,10 @@
+use rustc_errors::Diagnostic;
 use rustc_hir::attrs::diagnostic::Directive;
+use rustc_session::lint::builtin::MISPLACED_DIAGNOSTIC_ATTRIBUTES;
 
 use crate::attributes::diagnostic::*;
 use crate::attributes::prelude::*;
-
+use crate::errors::DiagnosticOnConstOnlyForTraitImpls;
 #[derive(Default)]
 pub(crate) struct OnConstParser {
     span: Option<Span>,
@@ -21,6 +23,21 @@ impl<S: Stage> AttributeParser<S> for OnConstParser {
 
             let span = cx.attr_span;
             this.span = Some(span);
+
+            // FIXME(mejrs) no constness field on `Target`,
+            // so non-constness is still checked in check_attr.rs
+            if !matches!(cx.target, Target::Impl { of_trait: true }) {
+                let target_span = cx.target_span;
+                cx.emit_dyn_lint(
+                    MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                    move |dcx, level| {
+                        DiagnosticOnConstOnlyForTraitImpls { target_span }.into_diag(dcx, level)
+                    },
+                    span,
+                );
+                return;
+            }
+
             let mode = Mode::DiagnosticOnConst;
 
             let Some(items) = parse_list(cx, args, mode) else { return };
@@ -32,7 +49,8 @@ impl<S: Stage> AttributeParser<S> for OnConstParser {
         },
     )];
 
-    //FIXME Still checked in `check_attr.rs`
+    // "Allowed" on all targets; noop on anything but non-const trait impls;
+    // this linted on in parser.
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {

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

@@ -1,10 +1,13 @@
+use rustc_errors::Diagnostic;
 use rustc_feature::template;
 use rustc_hir::attrs::AttributeKind;
+use rustc_session::lint::builtin::MISPLACED_DIAGNOSTIC_ATTRIBUTES;
 use rustc_span::sym;
 
 use crate::attributes::diagnostic::*;
 use crate::attributes::prelude::*;
 use crate::context::{AcceptContext, Stage};
+use crate::errors::DiagnosticOnMoveOnlyForAdt;
 use crate::parser::ArgParser;
 use crate::target_checking::{ALL_TARGETS, AllowedTargets};
 
@@ -29,6 +32,15 @@ impl OnMoveParser {
         let span = cx.attr_span;
         self.span = Some(span);
 
+        if !matches!(cx.target, Target::Enum | Target::Struct | Target::Union) {
+            cx.emit_dyn_lint(
+                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                move |dcx, level| DiagnosticOnMoveOnlyForAdt.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) {
@@ -44,6 +56,8 @@ impl<S: Stage> AttributeParser<S> for OnMoveParser {
             this.parse(cx, args, Mode::DiagnosticOnMove);
         },
     )];
+
+    // "Allowed" for all targets but noop if used on not-adt.
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {

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

@@ -1,7 +1,10 @@
+use rustc_errors::Diagnostic;
 use rustc_hir::attrs::diagnostic::Directive;
+use rustc_session::lint::builtin::MISPLACED_DIAGNOSTIC_ATTRIBUTES;
 
 use crate::attributes::diagnostic::*;
 use crate::attributes::prelude::*;
+use crate::errors::DiagnosticOnUnimplementedOnlyForTraits;
 
 #[derive(Default)]
 pub(crate) struct OnUnimplementedParser {
@@ -19,11 +22,12 @@ impl OnUnimplementedParser {
         let span = cx.attr_span;
         self.span = Some(span);
 
-        // If target is not a trait, returning early will make `finalize` emit a
-        // `AttributeKind::OnUnimplemented {span, directive: None }`, to prevent it being
-        // accidentally used on non-trait items like trait aliases.
         if !matches!(cx.target, Target::Trait) {
-            // Lint later emitted in check_attr
+            cx.emit_dyn_lint(
+                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                move |dcx, level| DiagnosticOnUnimplementedOnlyForTraits.into_diag(dcx, level),
+                span,
+            );
             return;
         }
 

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

@@ -252,3 +252,32 @@ pub(crate) struct DocUnknownAny {
 #[derive(Diagnostic)]
 #[diag("expected boolean for `#[doc(auto_cfg = ...)]`")]
 pub(crate) struct DocAutoCfgWrongLiteral;
+
+#[derive(Diagnostic)]
+#[diag("`#[diagnostic::on_const]` can only be applied to non-const trait implementations")]
+pub(crate) struct DiagnosticOnConstOnlyForTraitImpls {
+    #[label("not a trait implementation")]
+    pub target_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag("`#[diagnostic::on_move]` can only be applied to enums, structs or unions")]
+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,
+}
+
+#[derive(Diagnostic)]
+#[diag("`#[diagnostic::do_not_recommend]` can only be placed on trait implementations")]
+pub(crate) struct IncorrectDoNotRecommendLocation {
+    #[label("not a trait implementation")]
+    pub target_span: Span,
+}