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.

Author: weiznich

compiler/rustc_ast/src/attr/mod.rs

@@ -13,6 +13,7 @@ use crate::util::literal::escape_string_symbol;
 use rustc_index::bit_set::GrowableBitSet;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
+use smallvec::{smallvec, SmallVec};
 use std::iter;
 use std::sync::atomic::{AtomicU32, Ordering};
 use thin_vec::{thin_vec, ThinVec};
@@ -87,10 +88,20 @@ impl Attribute {
             AttrKind::DocComment(..) => None,
         }
     }
+
     pub fn name_or_empty(&self) -> Symbol {
         self.ident().unwrap_or_else(Ident::empty).name
     }
 
+    pub fn path(&self) -> SmallVec<[Symbol; 1]> {
+        match &self.kind {
+            AttrKind::Normal(normal) => {
+                normal.item.path.segments.iter().map(|s| s.ident.name).collect()
+            }
+            AttrKind::DocComment(..) => smallvec![sym::doc],
+        }
+    }
+
     #[inline]
     pub fn has_name(&self, name: Symbol) -> bool {
         match &self.kind {

compiler/rustc_feature/src/builtin_attrs.rs

@@ -515,12 +515,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes, experimental!(deprecated_safe),
     ),
 
-    // RFC 2397
-    gated!(
-        do_not_recommend, Normal, template!(Word), WarnFollowing,
-        EncodeCrossCrate::Yes, experimental!(do_not_recommend)
-    ),
-
     // `#[cfi_encoding = ""]`
     gated!(
         cfi_encoding, Normal, template!(NameValueStr: "encoding"), ErrorPreceding,

compiler/rustc_middle/src/ty/mod.rs

@@ -1805,6 +1805,11 @@ impl<'tcx> TyCtxt<'tcx> {
         self.get_attrs(did, attr).next().is_some()
     }
 
+    /// Determines whether an item is annotated with a multi-segement attribute
+    pub fn has_attrs_with_path(self, did: impl Into<DefId>, attrs: &[Symbol]) -> bool {
+        self.get_attrs_by_path(did.into(), attrs).next().is_some()
+    }
+
     /// Returns `true` if this is an `auto trait`.
     pub fn trait_is_auto(self, trait_def_id: DefId) -> bool {
         self.trait_def(trait_def_id).has_auto_impl

compiler/rustc_passes/messages.ftl

@@ -341,7 +341,7 @@ passes_implied_feature_not_exist =
     feature `{$implied_by}` implying `{$feature}` does not exist
 
 passes_incorrect_do_not_recommend_location =
-    `#[do_not_recommend]` can only be placed on trait implementations
+    `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
 
 passes_incorrect_meta_item = expected a quoted string literal
 passes_incorrect_meta_item_suggestion = consider surrounding this with quotes

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.

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)]

compiler/rustc_resolve/src/macros.rs

@@ -567,7 +567,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         if res == Res::NonMacroAttr(NonMacroAttrKind::Tool)
             && let [namespace, attribute, ..] = &*path.segments
             && namespace.ident.name == sym::diagnostic
-            && attribute.ident.name != sym::on_unimplemented
+            && !(attribute.ident.name == sym::on_unimplemented
+                || (attribute.ident.name == sym::do_not_recommend
+                    && self.tcx.features().do_not_recommend))
         {
             let distance =
                 edit_distance(attribute.ident.name.as_str(), sym::on_unimplemented.as_str(), 5);

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -380,7 +380,10 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
             source: CandidateSource::Impl(impl_def_id),
             result: _,
         } = candidate.kind()
-            && goal.infcx().tcx.has_attr(impl_def_id, sym::do_not_recommend)
+            && goal
+                .infcx()
+                .tcx
+                .has_attrs_with_path(impl_def_id, &[sym::diagnostic, sym::do_not_recommend])
         {
             return ControlFlow::Break(self.obligation.clone());
         }

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -1012,7 +1012,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         let mut base_cause = obligation.cause.code().clone();
         loop {
             if let ObligationCauseCode::ImplDerived(ref c) = base_cause {
-                if self.tcx.has_attr(c.impl_or_alias_def_id, sym::do_not_recommend) {
+                if self.tcx.has_attrs_with_path(
+                    c.impl_or_alias_def_id,
+                    &[sym::diagnostic, sym::do_not_recommend],
+                ) {
                     let code = (*c.derived.parent_code).clone();
                     obligation.cause.map_code(|_| code);
                     obligation.predicate = c.derived.parent_trait_pred.upcast(self.tcx);

tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs

@@ -26,7 +26,7 @@ impl<T> Expression for Bound<T> {
     type SqlType = T;
 }
 
-#[do_not_recommend]
+#[diagnostic::do_not_recommend]
 impl<T, ST> AsExpression<ST> for T
 where
     T: Expression<SqlType = ST>,