Check type_const type is ConstParamTy_ and that RHS matches it

Author: camelid

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

@@ -918,7 +918,10 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
                 );
                 check_where_clauses(wfcx, def_id);
 
-                wfcheck::check_const_item_rhs(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

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -951,16 +951,19 @@ pub(crate) fn check_associated_item(
                 let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), ty);
                 wfcx.register_wf_obligation(span, loc, ty.into());
 
-                if item.defaultness(tcx).has_value() {
+                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),
                     );
-
-                    check_const_item_rhs(wfcx, def_id)?;
                 }
 
                 Ok(())
@@ -1230,16 +1233,33 @@ pub(crate) fn check_static_item<'tcx>(
 }
 
 #[instrument(level = "debug", skip(wfcx))]
-pub(super) fn check_const_item_rhs<'tcx>(
+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();
-    if find_attr!(tcx.get_all_attrs(def_id), AttributeKind::TypeConst(_)) {
+    let span = tcx.def_span(def_id);
+
+    wfcx.register_bound(
+        ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(item_ty)),
+        wfcx.param_env,
+        item_ty,
+        tcx.require_lang_item(LangItem::ConstParamTy, span),
+    );
+
+    if has_value {
         let raw_ct = tcx.const_of_item(def_id).instantiate_identity();
-        let span = tcx.def_span(def_id);
         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());
+
+        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(())
 }

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

@@ -1257,12 +1257,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         ty: Ty<'tcx>,
         obligation: &PredicateObligation<'tcx>,
     ) -> Diag<'a> {
-        let param = obligation.cause.body_id;
-        let hir::GenericParamKind::Const { ty: &hir::Ty { span, .. }, .. } =
-            self.tcx.hir_node_by_def_id(param).expect_generic_param().kind
-        else {
-            bug!()
-        };
+        let def_id = obligation.cause.body_id;
+        let span = self.tcx.ty_span(def_id);
 
         let mut file = None;
         let ty_str = self.tcx.short_string(ty, &mut file);

tests/ui/associated-consts/assoc-const-eq-ambiguity.rs

@@ -1,7 +1,7 @@
 // We used to say "ambiguous associated type" on ambiguous associated consts.
 // Ensure that we now use the correct label.
 
-#![feature(associated_const_equality, min_generic_const_args)]
+#![feature(associated_const_equality, min_generic_const_args, unsized_const_params)]
 #![allow(incomplete_features)]
 
 trait Trait0: Parent0<i32> + Parent0<u32> {}

tests/ui/associated-consts/assoc-const-eq-bound-var-in-ty-not-wf.rs

@@ -1,9 +1,11 @@
 // Check that we eventually catch types of assoc const bounds
 // (containing late-bound vars) that are ill-formed.
-#![feature(associated_const_equality, min_generic_const_args)]
+#![feature(associated_const_equality, min_generic_const_args, adt_const_params, unsized_const_params)]
 #![allow(incomplete_features)]
 
-trait Trait<T> {
+use std::marker::ConstParamTy_;
+
+trait Trait<T: ConstParamTy_> {
     #[type_const]
     const K: T;
 }

tests/ui/associated-consts/assoc-const-eq-bound-var-in-ty-not-wf.stderr

@@ -1,19 +1,19 @@
 error: higher-ranked subtype error
-  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:14:13
+  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:16:13
    |
 LL |         K = { () }
    |             ^^^^^^
 
 error: higher-ranked subtype error
-  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:14:13
+  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:16:13
    |
 LL |         K = { () }
    |             ^^^^^^
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: implementation of `Project` is not general enough
-  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:12:13
+  --> $DIR/assoc-const-eq-bound-var-in-ty-not-wf.rs:14:13
    |
 LL |       _: impl Trait<
    |  _____________^

tests/ui/associated-consts/assoc-const-eq-bound-var-in-ty.rs

@@ -3,10 +3,12 @@
 //
 //@ check-pass
 
-#![feature(associated_const_equality, min_generic_const_args)]
+#![feature(associated_const_equality, min_generic_const_args, adt_const_params, unsized_const_params)]
 #![allow(incomplete_features)]
 
-trait Trait<T> {
+use std::marker::ConstParamTy_;
+
+trait Trait<T: ConstParamTy_> {
     #[type_const]
     const K: T;
 }

tests/ui/associated-consts/assoc-const-eq-esc-bound-var-in-ty.rs

@@ -1,6 +1,6 @@
 // Detect and reject escaping late-bound generic params in
 // the type of assoc consts used in an equality bound.
-#![feature(associated_const_equality, min_generic_const_args)]
+#![feature(associated_const_equality, min_generic_const_args, unsized_const_params)]
 #![allow(incomplete_features)]
 
 trait Trait<'a> {

tests/ui/associated-consts/assoc-const-eq-param-in-ty.rs

@@ -1,14 +1,16 @@
 // Regression test for issue #108271.
 // Detect and reject generic params in the type of assoc consts used in an equality bound.
-#![feature(associated_const_equality, min_generic_const_args)]
+#![feature(associated_const_equality, min_generic_const_args, adt_const_params, unsized_const_params)]
 #![allow(incomplete_features)]
 
-trait Trait<'a, T: 'a, const N: usize> {
+use std::marker::ConstParamTy_;
+
+trait Trait<'a, T: 'a + ConstParamTy_, const N: usize> {
     #[type_const]
     const K: &'a [T; N];
 }
 
-fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
+fn take0<'r, A: 'r + ConstParamTy_, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
 //~^ ERROR the type of the associated constant `K` must not depend on generic parameters
 //~| NOTE its type must not depend on the lifetime parameter `'r`
 //~| NOTE the lifetime parameter `'r` is defined here
@@ -22,7 +24,7 @@ fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
 //~| NOTE the const parameter `Q` is defined here
 //~| NOTE `K` has type `&'r [A; Q]`
 
-trait Project {
+trait Project: ConstParamTy_ {
     #[type_const]
     const SELF: Self;
 }
@@ -38,7 +40,7 @@ fn take2<P: Project<SELF = {}>>(_: P) {}
 //~| NOTE the type parameter `P` is defined here
 //~| NOTE `SELF` has type `P`
 
-trait Iface<'r> {
+trait Iface<'r>: ConstParamTy_ {
     //~^ NOTE the lifetime parameter `'r` is defined here
     //~| NOTE the lifetime parameter `'r` is defined here
     type Assoc<const Q: usize>: Trait<'r, Self, Q, K = { loop {} }>