Move `#[do_not_recommend]` to the `#[diagnostic]` namespace

This commit moves the `#[do_not_recommend]` attribute to the
`#[diagnostic]` namespace. It still requires
`#![feature(do_not_recommend)]` to work.

2 files changed, 77 insertions, 67 deletions

diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index aadbd747313..2eee1742b0d 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -116,92 +116,96 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         let mut seen = FxHashMap::default();
         let attrs = self.tcx.hir().attrs(hir_id);
         for attr in attrs {
-            if attr.path_matches(&[sym::diagnostic, sym::on_unimplemented]) {
-                self.check_diagnostic_on_unimplemented(attr.span, hir_id, target);
-            }
-            match attr.name_or_empty() {
-                sym::do_not_recommend => self.check_do_not_recommend(attr.span, target),
-                sym::inline => self.check_inline(hir_id, attr, span, target),
-                sym::coverage => self.check_coverage(hir_id, attr, span, target),
-                sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target),
-                sym::marker => self.check_marker(hir_id, attr, span, target),
-                sym::target_feature => self.check_target_feature(hir_id, attr, span, target, attrs),
-                sym::thread_local => self.check_thread_local(attr, span, target),
-                sym::track_caller => {
+            match attr.path().as_slice() {
+                [sym::diagnostic, sym::do_not_recommend] => {
+                    self.check_do_not_recommend(attr.span, hir_id, target)
+                }
+                [sym::diagnostic, sym::on_unimplemented] => {
+                    self.check_diagnostic_on_unimplemented(attr.span, hir_id, target)
+                }
+                [sym::inline] => self.check_inline(hir_id, attr, span, target),
+                [sym::coverage] => self.check_coverage(hir_id, attr, span, target),
+                [sym::non_exhaustive] => self.check_non_exhaustive(hir_id, attr, span, target),
+                [sym::marker] => self.check_marker(hir_id, attr, span, target),
+                [sym::target_feature] => {
+                    self.check_target_feature(hir_id, attr, span, target, attrs)
+                }
+                [sym::thread_local] => self.check_thread_local(attr, span, target),
+                [sym::track_caller] => {
                     self.check_track_caller(hir_id, attr.span, attrs, span, target)
                 }
-                sym::doc => self.check_doc_attrs(
+                [sym::doc] => self.check_doc_attrs(
                     attr,
                     hir_id,
                     target,
                     &mut specified_inline,
                     &mut doc_aliases,
                 ),
-                sym::no_link => self.check_no_link(hir_id, attr, span, target),
-                sym::export_name => self.check_export_name(hir_id, attr, span, target),
-                sym::rustc_layout_scalar_valid_range_start
-                | sym::rustc_layout_scalar_valid_range_end => {
+                [sym::no_link] => self.check_no_link(hir_id, attr, span, target),
+                [sym::export_name] => self.check_export_name(hir_id, attr, span, target),
+                [sym::rustc_layout_scalar_valid_range_start]
+                | [sym::rustc_layout_scalar_valid_range_end] => {
                     self.check_rustc_layout_scalar_valid_range(attr, span, target)
                 }
-                sym::allow_internal_unstable => {
+                [sym::allow_internal_unstable] => {
                     self.check_allow_internal_unstable(hir_id, attr, span, target, attrs)
                 }
-                sym::debugger_visualizer => self.check_debugger_visualizer(attr, target),
-                sym::rustc_allow_const_fn_unstable => {
+                [sym::debugger_visualizer] => self.check_debugger_visualizer(attr, target),
+                [sym::rustc_allow_const_fn_unstable] => {
                     self.check_rustc_allow_const_fn_unstable(hir_id, attr, span, target)
                 }
-                sym::rustc_std_internal_symbol => {
+                [sym::rustc_std_internal_symbol] => {
                     self.check_rustc_std_internal_symbol(attr, span, target)
                 }
-                sym::naked => self.check_naked(hir_id, attr, span, target),
-                sym::rustc_never_returns_null_ptr => {
+                [sym::naked] => self.check_naked(hir_id, attr, span, target),
+                [sym::rustc_never_returns_null_ptr] => {
                     self.check_applied_to_fn_or_method(hir_id, attr, span, target)
                 }
-                sym::rustc_legacy_const_generics => {
+                [sym::rustc_legacy_const_generics] => {
                     self.check_rustc_legacy_const_generics(hir_id, attr, span, target, item)
                 }
-                sym::rustc_lint_query_instability => {
+                [sym::rustc_lint_query_instability] => {
                     self.check_rustc_lint_query_instability(hir_id, attr, span, target)
                 }
-                sym::rustc_lint_diagnostics => {
+                [sym::rustc_lint_diagnostics] => {
                     self.check_rustc_lint_diagnostics(hir_id, attr, span, target)
                 }
-                sym::rustc_lint_opt_ty => self.check_rustc_lint_opt_ty(attr, span, target),
-                sym::rustc_lint_opt_deny_field_access => {
+                [sym::rustc_lint_opt_ty] => self.check_rustc_lint_opt_ty(attr, span, target),
+                [sym::rustc_lint_opt_deny_field_access] => {
                     self.check_rustc_lint_opt_deny_field_access(attr, span, target)
                 }
-                sym::rustc_clean
-                | sym::rustc_dirty
-                | sym::rustc_if_this_changed
-                | sym::rustc_then_this_would_need => self.check_rustc_dirty_clean(attr),
-                sym::rustc_coinductive
-                | sym::rustc_must_implement_one_of
-                | sym::rustc_deny_explicit_impl
-                | sym::const_trait => self.check_must_be_applied_to_trait(attr, span, target),
-                sym::cmse_nonsecure_entry => {
+                [sym::rustc_clean]
+                | [sym::rustc_dirty]
+                | [sym::rustc_if_this_changed]
+                | [sym::rustc_then_this_would_need] => self.check_rustc_dirty_clean(attr),
+                [sym::rustc_coinductive]
+                | [sym::rustc_must_implement_one_of]
+                | [sym::rustc_deny_explicit_impl]
+                | [sym::const_trait] => self.check_must_be_applied_to_trait(attr, span, target),
+                [sym::cmse_nonsecure_entry] => {
                     self.check_cmse_nonsecure_entry(hir_id, attr, span, target)
                 }
-                sym::collapse_debuginfo => self.check_collapse_debuginfo(attr, span, target),
-                sym::must_not_suspend => self.check_must_not_suspend(attr, span, target),
-                sym::must_use => self.check_must_use(hir_id, attr, target),
-                sym::rustc_pass_by_value => self.check_pass_by_value(attr, span, target),
-                sym::rustc_allow_incoherent_impl => {
+                [sym::collapse_debuginfo] => self.check_collapse_debuginfo(attr, span, target),
+                [sym::must_not_suspend] => self.check_must_not_suspend(attr, span, target),
+                [sym::must_use] => self.check_must_use(hir_id, attr, target),
+                [sym::rustc_pass_by_value] => self.check_pass_by_value(attr, span, target),
+                [sym::rustc_allow_incoherent_impl] => {
                     self.check_allow_incoherent_impl(attr, span, target)
                 }
-                sym::rustc_has_incoherent_inherent_impls => {
+                [sym::rustc_has_incoherent_inherent_impls] => {
                     self.check_has_incoherent_inherent_impls(attr, span, target)
                 }
-                sym::ffi_pure => self.check_ffi_pure(attr.span, attrs, target),
-                sym::ffi_const => self.check_ffi_const(attr.span, target),
-                sym::rustc_const_unstable
-                | sym::rustc_const_stable
-                | sym::unstable
-                | sym::stable
-                | sym::rustc_allowed_through_unstable_modules
-                | sym::rustc_promotable => self.check_stability_promotable(attr, target),
-                sym::link_ordinal => self.check_link_ordinal(attr, span, target),
-                sym::rustc_confusables => self.check_confusables(attr, target),
-                sym::rustc_safe_intrinsic => {
+                [sym::ffi_pure] => self.check_ffi_pure(attr.span, attrs, target),
+                [sym::ffi_const] => self.check_ffi_const(attr.span, target),
+                [sym::rustc_const_unstable]
+                | [sym::rustc_const_stable]
+                | [sym::unstable]
+                | [sym::stable]
+                | [sym::rustc_allowed_through_unstable_modules]
+                | [sym::rustc_promotable] => self.check_stability_promotable(attr, target),
+                [sym::link_ordinal] => self.check_link_ordinal(attr, span, target),
+                [sym::rustc_confusables] => self.check_confusables(attr, target),
+                [sym::rustc_safe_intrinsic] => {
                     self.check_rustc_safe_intrinsic(hir_id, attr, span, target)
                 }
                 _ => true,
@@ -293,18 +297,26 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         );
     }
 
-    /// Checks if `#[do_not_recommend]` is applied on a trait impl.
-    fn check_do_not_recommend(&self, attr_span: Span, target: Target) -> bool {
-        if let Target::Impl = target {
-            true
-        } else {
-            self.dcx().emit_err(errors::IncorrectDoNotRecommendLocation { span: attr_span });
-            false
+    /// Checks if `#[diagnostic::do_not_recommend]` is applied on a trait impl.
+    fn check_do_not_recommend(&self, attr_span: Span, hir_id: HirId, target: Target) -> bool {
+        if !matches!(target, Target::Impl) {
+            self.tcx.emit_node_span_lint(
+                UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,
+                hir_id,
+                attr_span,
+                errors::IncorrectDoNotRecommendLocation,
+            );
         }
+        true
     }
 
     /// Checks if `#[diagnostic::on_unimplemented]` is applied to a trait definition
-    fn check_diagnostic_on_unimplemented(&self, attr_span: Span, hir_id: HirId, target: Target) {
+    fn check_diagnostic_on_unimplemented(
+        &self,
+        attr_span: Span,
+        hir_id: HirId,
+        target: Target,
+    ) -> bool {
         if !matches!(target, Target::Trait) {
             self.tcx.emit_node_span_lint(
                 UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,
@@ -313,6 +325,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 DiagnosticOnUnimplementedOnlyForTraits,
             );
         }
+        true
     }
 
     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index b8586e7e974..180552785fe 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -17,12 +17,9 @@ use rustc_span::{Span, Symbol, DUMMY_SP};
 use crate::check_attr::ProcMacroKind;
 use crate::lang_items::Duplicate;
 
-#[derive(Diagnostic)]
+#[derive(LintDiagnostic)]
 #[diag(passes_incorrect_do_not_recommend_location)]
-pub struct IncorrectDoNotRecommendLocation {
-    #[primary_span]
-    pub span: Span,
-}
+pub struct IncorrectDoNotRecommendLocation;
 
 #[derive(LintDiagnostic)]
 #[diag(passes_outer_crate_level_attr)]