Rollup merge of rust-lang#148716 - camelid:finish-type_const, r=BoxyUwU

mgca: Finish implementation of `#[type_const]`

tracking issue: rust-lang#132980
fixes rust-lang#140729
fixes rust-lang#140860

- **Fix `#[type_const]` attribute placement validation**
- **Perform WF-checking on type_const RHS's**
- **Check type_const type is ConstParamTy_ and that RHS matches it**
- **Check that impls of `#[type_const]` consts also have the attr**

r? `@BoxyUwU`

Author: matthiaskrgr

compiler/rustc_attr_parsing/src/attributes/traits.rs

@@ -66,7 +66,8 @@ pub(crate) struct TypeConstParser;
 impl<S: Stage> NoArgsAttributeParser<S> for TypeConstParser {
     const PATH: &[Symbol] = &[sym::type_const];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::AssocConst)]);
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Const), Allow(Target::AssocConst)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::TypeConst;
 }
 

compiler/rustc_hir/src/hir.rs

@@ -3065,7 +3065,7 @@ macro_rules! expect_methods_self_kind {
         $(
             #[track_caller]
             pub fn $name(&self) -> $ret_ty {
-                let $pat = &self.kind else { expect_failed(stringify!($ident), self) };
+                let $pat = &self.kind else { expect_failed(stringify!($name), self) };
                 $ret_val
             }
         )*
@@ -3077,7 +3077,7 @@ macro_rules! expect_methods_self {
         $(
             #[track_caller]
             pub fn $name(&self) -> $ret_ty {
-                let $pat = self else { expect_failed(stringify!($ident), self) };
+                let $pat = self else { expect_failed(stringify!($name), self) };
                 $ret_val
             }
         )*
@@ -4790,6 +4790,11 @@ impl<'hir> Node<'hir> {
                 ForeignItemKind::Static(ty, ..) => Some(ty),
                 _ => None,
             },
+            Node::GenericParam(param) => match param.kind {
+                GenericParamKind::Lifetime { .. } => None,
+                GenericParamKind::Type { default, .. } => default,
+                GenericParamKind::Const { ty, .. } => Some(ty),
+            },
             _ => None,
         }
     }

compiler/rustc_hir_analysis/src/check/check.rs

@@ -757,22 +757,18 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
     }
 
     match tcx.def_kind(def_id) {
-        def_kind @ (DefKind::Static { .. } | DefKind::Const) => {
+        DefKind::Static { .. } => {
             tcx.ensure_ok().generics_of(def_id);
             tcx.ensure_ok().type_of(def_id);
             tcx.ensure_ok().predicates_of(def_id);
-            match def_kind {
-                DefKind::Static { .. } => {
-                    check_static_inhabited(tcx, def_id);
-                    check_static_linkage(tcx, def_id);
-                    let ty = tcx.type_of(def_id).instantiate_identity();
-                    res = res.and(wfcheck::check_static_item(
-                        tcx, def_id, ty, /* should_check_for_sync */ true,
-                    ));
-                }
-                DefKind::Const => res = res.and(wfcheck::check_const_item(tcx, def_id)),
-                _ => unreachable!(),
-            }
+
+            check_static_inhabited(tcx, def_id);
+            check_static_linkage(tcx, def_id);
+            let ty = tcx.type_of(def_id).instantiate_identity();
+            res = res.and(wfcheck::check_static_item(
+                tcx, def_id, ty, /* should_check_for_sync */ true,
+            ));
+
             // Only `Node::Item` and `Node::ForeignItem` still have HIR based
             // checks. Returning early here does not miss any checks and
             // avoids this query from having a direct dependency edge on the HIR
@@ -900,6 +896,39 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
             // avoids this query from having a direct dependency edge on the HIR
             return res;
         }
+        DefKind::Const => {
+            tcx.ensure_ok().generics_of(def_id);
+            tcx.ensure_ok().type_of(def_id);
+            tcx.ensure_ok().predicates_of(def_id);
+
+            res = res.and(enter_wf_checking_ctxt(tcx, def_id, |wfcx| {
+                let ty = tcx.type_of(def_id).instantiate_identity();
+                let ty_span = tcx.ty_span(def_id);
+                let ty = wfcx.deeply_normalize(ty_span, Some(WellFormedLoc::Ty(def_id)), ty);
+                wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(def_id)), ty.into());
+                wfcx.register_bound(
+                    traits::ObligationCause::new(
+                        ty_span,
+                        def_id,
+                        ObligationCauseCode::SizedConstOrStatic,
+                    ),
+                    tcx.param_env(def_id),
+                    ty,
+                    tcx.require_lang_item(LangItem::Sized, ty_span),
+                );
+                check_where_clauses(wfcx, def_id);
+
+                if find_attr!(tcx.get_all_attrs(def_id), AttributeKind::TypeConst(_)) {
+                    wfcheck::check_type_const(wfcx, def_id, ty, true)?;
+                }
+                Ok(())
+            }));
+
+            // Only `Node::Item` and `Node::ForeignItem` still have HIR based
+            // checks. Returning early here does not miss any checks and
+            // avoids this query from having a direct dependency edge on the HIR
+            return res;
+        }
         DefKind::TyAlias => {
             tcx.ensure_ok().generics_of(def_id);
             tcx.ensure_ok().type_of(def_id);
@@ -920,6 +949,11 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
                 }));
                 check_variances_for_type_defn(tcx, def_id);
             }
+
+            // Only `Node::Item` and `Node::ForeignItem` still have HIR based
+            // checks. Returning early here does not miss any checks and
+            // avoids this query from having a direct dependency edge on the HIR
+            return res;
         }
         DefKind::ForeignMod => {
             let it = tcx.hir_expect_item(def_id);

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -6,9 +6,10 @@ use hir::def_id::{DefId, DefIdMap, LocalDefId};
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, ErrorGuaranteed, MultiSpan, pluralize, struct_span_code_err};
+use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::VisitorExt;
-use rustc_hir::{self as hir, AmbigArg, GenericParamKind, ImplItemKind, intravisit};
+use rustc_hir::{self as hir, AmbigArg, GenericParamKind, ImplItemKind, find_attr, intravisit};
 use rustc_infer::infer::{self, BoundRegionConversionTime, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
@@ -1984,12 +1985,46 @@ fn compare_impl_const<'tcx>(
     trait_const_item: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
+    compare_type_const(tcx, impl_const_item, trait_const_item)?;
     compare_number_of_generics(tcx, impl_const_item, trait_const_item, false)?;
     compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, false)?;
     check_region_bounds_on_impl_item(tcx, impl_const_item, trait_const_item, false)?;
     compare_const_predicate_entailment(tcx, impl_const_item, trait_const_item, impl_trait_ref)
 }
 
+fn compare_type_const<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    impl_const_item: ty::AssocItem,
+    trait_const_item: ty::AssocItem,
+) -> Result<(), ErrorGuaranteed> {
+    let impl_is_type_const =
+        find_attr!(tcx.get_all_attrs(impl_const_item.def_id), AttributeKind::TypeConst(_));
+    let trait_type_const_span = find_attr!(
+        tcx.get_all_attrs(trait_const_item.def_id),
+        AttributeKind::TypeConst(sp) => *sp
+    );
+
+    if let Some(trait_type_const_span) = trait_type_const_span
+        && !impl_is_type_const
+    {
+        return Err(tcx
+            .dcx()
+            .struct_span_err(
+                tcx.def_span(impl_const_item.def_id),
+                "implementation of `#[type_const]` const must be marked with `#[type_const]`",
+            )
+            .with_span_note(
+                MultiSpan::from_spans(vec![
+                    tcx.def_span(trait_const_item.def_id),
+                    trait_type_const_span,
+                ]),
+                "trait declaration of const is marked with `#[type_const]`",
+            )
+            .emit());
+    }
+    Ok(())
+}
+
 /// The equivalent of [compare_method_predicate_entailment], but for associated constants
 /// instead of associated functions.
 // FIXME(generic_const_items): If possible extract the common parts of `compare_{type,const}_predicate_entailment`.

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -6,10 +6,11 @@ use rustc_abi::ExternAbi;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, ErrorGuaranteed, pluralize, struct_span_code_err};
+use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
-use rustc_hir::{AmbigArg, ItemKind};
+use rustc_hir::{AmbigArg, ItemKind, find_attr};
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::{self, InferCtxt, SubregionOrigin, TyCtxtInferExt};
 use rustc_lint_defs::builtin::SUPERTRAIT_ITEM_SHADOWING_DEFINITION;
@@ -925,11 +926,11 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &ty::GenericParamDef) -> Result<(), Er
 #[instrument(level = "debug", skip(tcx))]
 pub(crate) fn check_associated_item(
     tcx: TyCtxt<'_>,
-    item_id: LocalDefId,
+    def_id: LocalDefId,
 ) -> Result<(), ErrorGuaranteed> {
-    let loc = Some(WellFormedLoc::Ty(item_id));
-    enter_wf_checking_ctxt(tcx, item_id, |wfcx| {
-        let item = tcx.associated_item(item_id);
+    let loc = Some(WellFormedLoc::Ty(def_id));
+    enter_wf_checking_ctxt(tcx, def_id, |wfcx| {
+        let item = tcx.associated_item(def_id);
 
         // Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
         // other `Foo` impls are incoherent.
@@ -942,36 +943,45 @@ pub(crate) fn check_associated_item(
             }
         };
 
-        let span = tcx.def_span(item_id);
+        let span = tcx.def_span(def_id);
 
         match item.kind {
             ty::AssocKind::Const { .. } => {
-                let ty = tcx.type_of(item.def_id).instantiate_identity();
-                let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
+                let ty = tcx.type_of(def_id).instantiate_identity();
+                let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), ty);
                 wfcx.register_wf_obligation(span, loc, ty.into());
-                check_sized_if_body(
-                    wfcx,
-                    item.def_id.expect_local(),
-                    ty,
-                    Some(span),
-                    ObligationCauseCode::SizedConstOrStatic,
-                );
+
+                let has_value = item.defaultness(tcx).has_value();
+                if find_attr!(tcx.get_all_attrs(def_id), AttributeKind::TypeConst(_)) {
+                    check_type_const(wfcx, def_id, ty, has_value)?;
+                }
+
+                if has_value {
+                    let code = ObligationCauseCode::SizedConstOrStatic;
+                    wfcx.register_bound(
+                        ObligationCause::new(span, def_id, code),
+                        wfcx.param_env,
+                        ty,
+                        tcx.require_lang_item(LangItem::Sized, span),
+                    );
+                }
+
                 Ok(())
             }
             ty::AssocKind::Fn { .. } => {
-                let sig = tcx.fn_sig(item.def_id).instantiate_identity();
+                let sig = tcx.fn_sig(def_id).instantiate_identity();
                 let hir_sig =
-                    tcx.hir_node_by_def_id(item_id).fn_sig().expect("bad signature for method");
-                check_fn_or_method(wfcx, sig, hir_sig.decl, item_id);
+                    tcx.hir_node_by_def_id(def_id).fn_sig().expect("bad signature for method");
+                check_fn_or_method(wfcx, sig, hir_sig.decl, def_id);
                 check_method_receiver(wfcx, hir_sig, item, self_ty)
             }
             ty::AssocKind::Type { .. } => {
                 if let ty::AssocContainer::Trait = item.container {
                     check_associated_type_bounds(wfcx, item, span)
                 }
                 if item.defaultness(tcx).has_value() {
-                    let ty = tcx.type_of(item.def_id).instantiate_identity();
-                    let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
+                    let ty = tcx.type_of(def_id).instantiate_identity();
+                    let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), ty);
                     wfcx.register_wf_obligation(span, loc, ty.into());
                 }
                 Ok(())
@@ -1222,28 +1232,36 @@ pub(crate) fn check_static_item<'tcx>(
     })
 }
 
-pub(crate) fn check_const_item(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
-    enter_wf_checking_ctxt(tcx, def_id, |wfcx| {
-        let ty = tcx.type_of(def_id).instantiate_identity();
-        let ty_span = tcx.ty_span(def_id);
-        let ty = wfcx.deeply_normalize(ty_span, Some(WellFormedLoc::Ty(def_id)), ty);
+#[instrument(level = "debug", skip(wfcx))]
+pub(super) fn check_type_const<'tcx>(
+    wfcx: &WfCheckingCtxt<'_, 'tcx>,
+    def_id: LocalDefId,
+    item_ty: Ty<'tcx>,
+    has_value: bool,
+) -> Result<(), ErrorGuaranteed> {
+    let tcx = wfcx.tcx();
+    let span = tcx.def_span(def_id);
 
-        wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(def_id)), ty.into());
-        wfcx.register_bound(
-            traits::ObligationCause::new(
-                ty_span,
-                wfcx.body_def_id,
-                ObligationCauseCode::SizedConstOrStatic,
-            ),
-            wfcx.param_env,
-            ty,
-            tcx.require_lang_item(LangItem::Sized, ty_span),
-        );
+    wfcx.register_bound(
+        ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(item_ty)),
+        wfcx.param_env,
+        item_ty,
+        tcx.require_lang_item(LangItem::ConstParamTy, span),
+    );
 
-        check_where_clauses(wfcx, def_id);
+    if has_value {
+        let raw_ct = tcx.const_of_item(def_id).instantiate_identity();
+        let norm_ct = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), raw_ct);
+        wfcx.register_wf_obligation(span, Some(WellFormedLoc::Ty(def_id)), norm_ct.into());
 
-        Ok(())
-    })
+        wfcx.register_obligation(Obligation::new(
+            tcx,
+            ObligationCause::new(span, def_id, ObligationCauseCode::WellFormed(None)),
+            wfcx.param_env,
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(norm_ct, item_ty)),
+        ));
+    }
+    Ok(())
 }
 
 #[instrument(level = "debug", skip(tcx, impl_))]
@@ -1583,33 +1601,16 @@ fn check_fn_or_method<'tcx>(
     }
 
     // If the function has a body, additionally require that the return type is sized.
-    check_sized_if_body(
-        wfcx,
-        def_id,
-        sig.output(),
-        match hir_decl.output {
-            hir::FnRetTy::Return(ty) => Some(ty.span),
-            hir::FnRetTy::DefaultReturn(_) => None,
-        },
-        ObligationCauseCode::SizedReturnType,
-    );
-}
-
-fn check_sized_if_body<'tcx>(
-    wfcx: &WfCheckingCtxt<'_, 'tcx>,
-    def_id: LocalDefId,
-    ty: Ty<'tcx>,
-    maybe_span: Option<Span>,
-    code: ObligationCauseCode<'tcx>,
-) {
-    let tcx = wfcx.tcx();
     if let Some(body) = tcx.hir_maybe_body_owned_by(def_id) {
-        let span = maybe_span.unwrap_or(body.value.span);
+        let span = match hir_decl.output {
+            hir::FnRetTy::Return(ty) => ty.span,
+            hir::FnRetTy::DefaultReturn(_) => body.value.span,
+        };
 
         wfcx.register_bound(
-            ObligationCause::new(span, def_id, code),
+            ObligationCause::new(span, def_id, ObligationCauseCode::SizedReturnType),
             wfcx.param_env,
-            ty,
+            sig.output(),
             tcx.require_lang_item(LangItem::Sized, span),
         );
     }

compiler/rustc_hir_analysis/src/collect.rs

@@ -1611,8 +1611,12 @@ fn const_of_item<'tcx>(
     };
     let ct_arg = match ct_rhs {
         hir::ConstItemRhs::TypeConst(ct_arg) => ct_arg,
-        hir::ConstItemRhs::Body(body_id) => {
-            bug!("cannot call const_of_item on a non-type_const {body_id:?}")
+        hir::ConstItemRhs::Body(_) => {
+            let e = tcx.dcx().span_delayed_bug(
+                tcx.def_span(def_id),
+                "cannot call const_of_item on a non-type_const",
+            );
+            return ty::EarlyBinder::bind(Const::new_error(tcx, e));
         }
     };
     let icx = ItemCtxt::new(tcx, def_id);