Rollup merge of #103827 - compiler-errors:rpitit-substs-compat, r=wesleywiser

Properly remap and check for substs compatibility in `confirm_impl_trait_in_trait_candidate`

Fixes #103824

1 files changed, 22 insertions, 3 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 7f829e46bbb..572f82117cc 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -2187,7 +2187,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
 // Verify that the trait item and its implementation have compatible substs lists
 fn check_substs_compatible<'tcx>(
     tcx: TyCtxt<'tcx>,
-    assoc_ty: &ty::AssocItem,
+    assoc_item: &ty::AssocItem,
     substs: ty::SubstsRef<'tcx>,
 ) -> bool {
     fn check_substs_compatible_inner<'tcx>(
@@ -2219,7 +2219,10 @@ fn check_substs_compatible<'tcx>(
         true
     }
 
-    check_substs_compatible_inner(tcx, tcx.generics_of(assoc_ty.def_id), substs.as_slice())
+    let generics = tcx.generics_of(assoc_item.def_id);
+    // Chop off any additional substs (RPITIT) substs
+    let substs = &substs[0..generics.count().min(substs.len())];
+    check_substs_compatible_inner(tcx, generics, substs)
 }
 
 fn confirm_impl_trait_in_trait_candidate<'tcx>(
@@ -2248,11 +2251,27 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         };
     }
 
-    let impl_fn_def_id = leaf_def.item.def_id;
     // Rebase from {trait}::{fn}::{opaque} to {impl}::{fn}::{opaque},
     // since `data.substs` are the impl substs.
     let impl_fn_substs =
         obligation.predicate.substs.rebase_onto(tcx, tcx.parent(trait_fn_def_id), data.substs);
+    let impl_fn_substs = translate_substs(
+        selcx.infcx(),
+        obligation.param_env,
+        data.impl_def_id,
+        impl_fn_substs,
+        leaf_def.defining_node,
+    );
+
+    if !check_substs_compatible(tcx, &leaf_def.item, impl_fn_substs) {
+        let err = tcx.ty_error_with_message(
+            obligation.cause.span,
+            "impl method and trait method have different parameters",
+        );
+        return Progress { term: err.into(), obligations };
+    }
+
+    let impl_fn_def_id = leaf_def.item.def_id;
 
     let cause = ObligationCause::new(
         obligation.cause.span,