Rollup merge of #109151 - compiler-errors:debug-assert-alias, r=WaffleLapkin

Assert def-kind is correct for alias types

Make sure we're not constructing alias types for the wrong def-kind, at least for debug cases 😅

compiler/rustc_infer/src/infer/at.rs

@@ -84,7 +84,6 @@ impl<'tcx> InferCtxt<'tcx> {
 
 pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -233,7 +232,7 @@ impl<'a, 'tcx> At<'a, 'tcx> {
     where
         T: ToTrace<'tcx>,
     {
-        let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b);
+        let trace = ToTrace::to_trace(self.cause, a_is_expected, a, b);
         Trace { at: self, trace, a_is_expected }
     }
 }
@@ -306,7 +305,6 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -314,10 +312,10 @@ impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
     ) -> TypeTrace<'tcx> {
         match (a, b) {
             (ImplSubject::Trait(trait_ref_a), ImplSubject::Trait(trait_ref_b)) => {
-                ToTrace::to_trace(tcx, cause, a_is_expected, trait_ref_a, trait_ref_b)
+                ToTrace::to_trace(cause, a_is_expected, trait_ref_a, trait_ref_b)
             }
             (ImplSubject::Inherent(ty_a), ImplSubject::Inherent(ty_b)) => {
-                ToTrace::to_trace(tcx, cause, a_is_expected, ty_a, ty_b)
+                ToTrace::to_trace(cause, a_is_expected, ty_a, ty_b)
             }
             (ImplSubject::Trait(_), ImplSubject::Inherent(_))
             | (ImplSubject::Inherent(_), ImplSubject::Trait(_)) => {
@@ -329,7 +327,6 @@ impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -344,7 +341,6 @@ impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -356,7 +352,6 @@ impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -371,7 +366,6 @@ impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -399,7 +393,6 @@ impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -411,7 +404,6 @@ impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -426,7 +418,6 @@ impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -441,24 +432,17 @@ impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::AliasTy<'tcx> {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
         b: Self,
     ) -> TypeTrace<'tcx> {
-        let a_ty = tcx.mk_projection(a.def_id, a.substs);
+        TypeTrace { cause: cause.clone(), values: Aliases(ExpectedFound::new(a_is_expected, a, b)) }
-        let b_ty = tcx.mk_projection(b.def_id, b.substs);
-        TypeTrace {
-            cause: cause.clone(),
-            values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),
-        }
     }
 }
 
 impl<'tcx> ToTrace<'tcx> for ty::FnSig<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1568,6 +1568,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     ValuePairs::TraitRefs(_) | ValuePairs::PolyTraitRefs(_) => {
                         (false, Mismatch::Fixed("trait"))
                     }
+                    ValuePairs::Aliases(infer::ExpectedFound { expected, .. }) => {
+                        (false, Mismatch::Fixed(self.tcx.def_descr(expected.def_id)))
+                    }
                     ValuePairs::Regions(_) => (false, Mismatch::Fixed("lifetime")),
                 };
                 let Some(vals) = self.values_str(values) else {
@@ -2124,6 +2127,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         match values {
             infer::Regions(exp_found) => self.expected_found_str(exp_found),
             infer::Terms(exp_found) => self.expected_found_str_term(exp_found),
+            infer::Aliases(exp_found) => self.expected_found_str(exp_found),
             infer::TraitRefs(exp_found) => {
                 let pretty_exp_found = ty::error::ExpectedFound {
                     expected: exp_found.expected.print_only_trait_path(),

compiler/rustc_infer/src/infer/mod.rs

@@ -338,6 +338,7 @@ pub struct InferCtxt<'tcx> {
 pub enum ValuePairs<'tcx> {
     Regions(ExpectedFound<ty::Region<'tcx>>),
     Terms(ExpectedFound<ty::Term<'tcx>>),
+    Aliases(ExpectedFound<ty::AliasTy<'tcx>>),
     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
     Sigs(ExpectedFound<ty::FnSig<'tcx>>),

compiler/rustc_middle/src/ty/context.rs

@@ -71,6 +71,7 @@ use rustc_type_ir::WithCachedTypeInfo;
 use rustc_type_ir::{CollectAndApply, DynKind, Interner, TypeFlags};
 
 use std::any::Any;
+use std::assert_matches::debug_assert_matches;
 use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::fmt;
@@ -2049,6 +2050,12 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_alias(self, kind: ty::AliasKind, alias_ty: ty::AliasTy<'tcx>) -> Ty<'tcx> {
+        debug_assert_matches!(
+            (kind, self.def_kind(alias_ty.def_id)),
+            (ty::Opaque, DefKind::OpaqueTy)
+                | (ty::Projection, DefKind::AssocTy)
+                | (ty::Opaque | ty::Projection, DefKind::ImplTraitPlaceholder)
+        );
         self.mk_ty_from_kind(Alias(kind, alias_ty))
     }