Auto merge of #152373 - Zalathar:rollup-wDsfoHs, r=Zalathar

Rollup of 4 pull requests

Successful merges:

 - #150823 (Implement MVP for opaque generic const arguments)
 - #152071 (Implement stdio FD constants)
 - #152171 (Port `rustc_strict_coherence` to the new attribute parser)
 - #152291 (Port `rustc_insignificant_dtor`)

Failed merges:

 - #152180 (Port `rustc_reservation_impl` to the new attribute parser)

Author: bors

compiler/rustc_ast_passes/src/errors.rs

@@ -950,6 +950,16 @@ pub(crate) struct IncompatibleFeatures {
     pub f2: Symbol,
 }
 
+#[derive(Diagnostic)]
+#[diag("`{$parent}` requires {$missing} to be enabled")]
+#[help("enable all of these features")]
+pub(crate) struct MissingDependentFeatures {
+    #[primary_span]
+    pub parent_span: Span,
+    pub parent: Symbol,
+    pub missing: String,
+}
+
 #[derive(Diagnostic)]
 #[diag("negative bounds are not supported")]
 pub(crate) struct NegativeBoundUnsupported {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -441,6 +441,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     maybe_stage_features(sess, features, krate);
     check_incompatible_features(sess, features);
+    check_dependent_features(sess, features);
     check_new_solver_banned_features(sess, features);
 
     let mut visitor = PostExpansionVisitor { sess, features };
@@ -649,6 +650,27 @@ fn check_incompatible_features(sess: &Session, features: &Features) {
     }
 }
 
+fn check_dependent_features(sess: &Session, features: &Features) {
+    for &(parent, children) in
+        rustc_feature::DEPENDENT_FEATURES.iter().filter(|(parent, _)| features.enabled(*parent))
+    {
+        if children.iter().any(|f| !features.enabled(*f)) {
+            let parent_span = features
+                .enabled_features_iter_stable_order()
+                .find_map(|(name, span)| (name == parent).then_some(span))
+                .unwrap();
+            // FIXME: should probably format this in fluent instead of here
+            let missing = children
+                .iter()
+                .filter(|f| !features.enabled(**f))
+                .map(|s| format!("`{}`", s.as_str()))
+                .intersperse(String::from(", "))
+                .collect();
+            sess.dcx().emit_err(errors::MissingDependentFeatures { parent_span, parent, missing });
+        }
+    }
+}
+
 fn check_new_solver_banned_features(sess: &Session, features: &Features) {
     if !sess.opts.unstable_opts.next_solver.globally {
         return;

compiler/rustc_ast_passes/src/lib.rs

@@ -5,6 +5,7 @@
 // tidy-alphabetical-start
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
+#![feature(iter_intersperse)]
 #![feature(iter_is_partitioned)]
 // tidy-alphabetical-end
 

compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

@@ -739,6 +739,19 @@ impl<S: Stage> CombineAttributeParser<S> for RustcThenThisWouldNeedParser {
     }
 }
 
+pub(crate) struct RustcInsignificantDtorParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for RustcInsignificantDtorParser {
+    const PATH: &[Symbol] = &[sym::rustc_insignificant_dtor];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Enum),
+        Allow(Target::Struct),
+        Allow(Target::ForeignTy),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcInsignificantDtor;
+}
+
 pub(crate) struct RustcEffectiveVisibilityParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for RustcEffectiveVisibilityParser {
@@ -845,3 +858,18 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcIntrinsicConstStableIndirectPar
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcIntrinsicConstStableIndirect;
 }
+
+pub(crate) struct RustcStrictCoherenceParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for RustcStrictCoherenceParser {
+    const PATH: &[Symbol] = &[sym::rustc_strict_coherence];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Trait),
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::Union),
+        Allow(Target::ForeignTy),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcStrictCoherence;
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -272,6 +272,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcEvaluateWhereClausesParser>>,
         Single<WithoutArgs<RustcHasIncoherentInherentImplsParser>>,
         Single<WithoutArgs<RustcHiddenTypeOfOpaquesParser>>,
+        Single<WithoutArgs<RustcInsignificantDtorParser>>,
         Single<WithoutArgs<RustcIntrinsicConstStableIndirectParser>>,
         Single<WithoutArgs<RustcIntrinsicParser>>,
         Single<WithoutArgs<RustcLintOptTyParser>>,
@@ -289,6 +290,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcReallocatorParser>>,
         Single<WithoutArgs<RustcRegionsParser>>,
         Single<WithoutArgs<RustcShouldNotBeCalledOnConstItems>>,
+        Single<WithoutArgs<RustcStrictCoherenceParser>>,
         Single<WithoutArgs<RustcVarianceOfOpaquesParser>>,
         Single<WithoutArgs<RustcVarianceParser>>,
         Single<WithoutArgs<SpecializationTraitParser>>,

compiler/rustc_feature/src/lib.rs

@@ -136,5 +136,6 @@ pub use builtin_attrs::{
 };
 pub use removed::REMOVED_LANG_FEATURES;
 pub use unstable::{
-    EnabledLangFeature, EnabledLibFeature, Features, INCOMPATIBLE_FEATURES, UNSTABLE_LANG_FEATURES,
+    DEPENDENT_FEATURES, EnabledLangFeature, EnabledLibFeature, Features, INCOMPATIBLE_FEATURES,
+    UNSTABLE_LANG_FEATURES,
 };

compiler/rustc_feature/src/unstable.rs

@@ -605,6 +605,8 @@ declare_features! (
     (unstable, offset_of_enum, "1.75.0", Some(120141)),
     /// Allows using fields with slice type in offset_of!
     (unstable, offset_of_slice, "1.81.0", Some(126151)),
+    /// Allows using generics in more complex const expressions, based on definitional equality.
+    (unstable, opaque_generic_const_args, "CURRENT_RUSTC_VERSION", Some(151972)),
     /// Allows using `#[optimize(X)]`.
     (unstable, optimize_attribute, "1.34.0", Some(54882)),
     /// Allows specifying nop padding on functions for dynamic patching.
@@ -782,3 +784,9 @@ pub const INCOMPATIBLE_FEATURES: &[(Symbol, Symbol)] = &[
     // boolean logic required to tell which typing rules to use.
     (sym::ref_pat_eat_one_layer_2024, sym::ref_pat_eat_one_layer_2024_structural),
 ];
+
+/// Some features require one or more other features to be enabled.
+pub const DEPENDENT_FEATURES: &[(Symbol, &[Symbol])] = &[
+    (sym::opaque_generic_const_args, &[sym::min_generic_const_args]),
+    (sym::unsized_const_params, &[sym::adt_const_params]),
+];

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1126,6 +1126,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_if_this_changed]`
     RustcIfThisChanged(Span, Option<Symbol>),
 
+    /// Represents `#[rustc_insignificant_dtor]`
+    RustcInsignificantDtor,
+
     /// Represents `#[rustc_intrinsic]`
     RustcIntrinsic,
 
@@ -1239,6 +1242,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_std_internal_symbol]`.
     RustcStdInternalSymbol(Span),
 
+    /// Represents `#[rustc_strict_coherence]`.
+    RustcStrictCoherence(Span),
+
     /// Represents `#[rustc_symbol_name]`
     RustcSymbolName(Span),
 
@@ -1275,6 +1281,7 @@ pub enum AttributeKind {
         /// Span of the attribute.
         span: Span,
     },
+
     /// Represents `#[target_feature(enable = "...")]` and
     /// `#[unsafe(force_target_feature(enable = "...")]`.
     TargetFeature { features: ThinVec<(Symbol, Span)>, attr_span: Span, was_forced: bool },

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -120,6 +120,7 @@ impl AttributeKind {
             RustcHasIncoherentInherentImpls => Yes,
             RustcHiddenTypeOfOpaques => No,
             RustcIfThisChanged(..) => No,
+            RustcInsignificantDtor => Yes,
             RustcIntrinsic => Yes,
             RustcIntrinsicConstStableIndirect => No,
             RustcLayout(..) => No,
@@ -156,6 +157,7 @@ impl AttributeKind {
             RustcSkipDuringMethodDispatch { .. } => No,
             RustcSpecializationTrait(..) => No,
             RustcStdInternalSymbol(..) => No,
+            RustcStrictCoherence(..) => Yes,
             RustcSymbolName(..) => Yes,
             RustcThenThisWouldNeed(..) => No,
             RustcUnsafeSpecializationMarker(..) => No,

compiler/rustc_hir_analysis/src/collect.rs

@@ -16,7 +16,7 @@
 
 use std::cell::Cell;
 use std::iter;
-use std::ops::Bound;
+use std::ops::{Bound, ControlFlow};
 
 use rustc_abi::{ExternAbi, Size};
 use rustc_ast::Recovered;
@@ -26,12 +26,13 @@ use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, E0228, ErrorGuaranteed, StashKey, struct_span_code_err,
 };
 use rustc_hir::attrs::AttributeKind;
-use rustc_hir::def::DefKind;
+use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_hir::intravisit::{InferKind, Visitor, VisitorExt};
+use rustc_hir::intravisit::{self, InferKind, Visitor, VisitorExt};
 use rustc_hir::{self as hir, GenericParamKind, HirId, Node, PreciseCapturingArgKind, find_attr};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::{DynCompatibilityViolation, ObligationCause};
+use rustc_middle::hir::nested_filter;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::util::{Discr, IntTypeExt};
 use rustc_middle::ty::{
@@ -1511,6 +1512,20 @@ fn anon_const_kind<'tcx>(tcx: TyCtxt<'tcx>, def: LocalDefId) -> ty::AnonConstKin
             let parent_hir_node = tcx.hir_node(tcx.parent_hir_id(const_arg_id));
             if tcx.features().generic_const_exprs() {
                 ty::AnonConstKind::GCE
+            } else if tcx.features().opaque_generic_const_args() {
+                // Only anon consts that are the RHS of a const item can be OGCA.
+                // Note: We can't just check tcx.parent because it needs to be EXACTLY
+                // the RHS, not just part of the RHS.
+                if !is_anon_const_rhs_of_const_item(tcx, def) {
+                    return ty::AnonConstKind::MCG;
+                }
+
+                let body = tcx.hir_body_owned_by(def);
+                let mut visitor = OGCAParamVisitor(tcx);
+                match visitor.visit_body(body) {
+                    ControlFlow::Break(UsesParam) => ty::AnonConstKind::OGCA,
+                    ControlFlow::Continue(()) => ty::AnonConstKind::MCG,
+                }
             } else if tcx.features().min_generic_const_args() {
                 ty::AnonConstKind::MCG
             } else if let hir::Node::Expr(hir::Expr {
@@ -1528,6 +1543,49 @@ fn anon_const_kind<'tcx>(tcx: TyCtxt<'tcx>, def: LocalDefId) -> ty::AnonConstKin
     }
 }
 
+fn is_anon_const_rhs_of_const_item<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> bool {
+    let hir_id = tcx.local_def_id_to_hir_id(def_id);
+    let Some((_, grandparent_node)) = tcx.hir_parent_iter(hir_id).nth(1) else { return false };
+    let (Node::Item(hir::Item { kind: hir::ItemKind::Const(_, _, _, ct_rhs), .. })
+    | Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(_, ct_rhs), .. })
+    | Node::TraitItem(hir::TraitItem {
+        kind: hir::TraitItemKind::Const(_, Some(ct_rhs)), ..
+    })) = grandparent_node
+    else {
+        return false;
+    };
+    let hir::ConstItemRhs::TypeConst(hir::ConstArg {
+        kind: hir::ConstArgKind::Anon(rhs_anon), ..
+    }) = ct_rhs
+    else {
+        return false;
+    };
+    def_id == rhs_anon.def_id
+}
+
+struct OGCAParamVisitor<'tcx>(TyCtxt<'tcx>);
+
+struct UsesParam;
+
+impl<'tcx> Visitor<'tcx> for OGCAParamVisitor<'tcx> {
+    type NestedFilter = nested_filter::OnlyBodies;
+    type Result = ControlFlow<UsesParam>;
+
+    fn maybe_tcx(&mut self) -> TyCtxt<'tcx> {
+        self.0
+    }
+
+    fn visit_path(&mut self, path: &hir::Path<'tcx>, _id: HirId) -> ControlFlow<UsesParam> {
+        if let Res::Def(DefKind::TyParam | DefKind::ConstParam | DefKind::LifetimeParam, _) =
+            path.res
+        {
+            return ControlFlow::Break(UsesParam);
+        }
+
+        intravisit::walk_path(self, path)
+    }
+}
+
 #[instrument(level = "debug", skip(tcx), ret)]
 fn const_of_item<'tcx>(
     tcx: TyCtxt<'tcx>,