Rollup merge of #125664 - compiler-errors:trace-tweaks, r=lcnr

Tweak relations to no longer rely on `TypeTrace`

Remove `At::trace`, and inline all of the `Trace::equate`,etc methods into `At`.

The only nontrivial change is that we use `AliasTerm` to relate two unevaluated consts in the old-solver impl of `ConstEquate`, since `AliasTerm` does implement `ToTrace` and will relate the args structurally (shallowly).

r? lcnr

compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs

@@ -363,7 +363,6 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         for (&orig, response) in iter::zip(original_values, var_values.var_values) {
             let InferOk { value: (), obligations } = infcx
                 .at(&cause, param_env)
-                .trace(orig, response)
                 .eq_structurally_relating_aliases(orig, response)
                 .unwrap();
             assert!(obligations.is_empty());

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -776,7 +776,6 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
             let InferOk { value: (), obligations } = self
                 .infcx
                 .at(&ObligationCause::dummy(), param_env)
-                .trace(term, ctor_term)
                 .eq_structurally_relating_aliases(term, ctor_term)?;
             debug_assert!(obligations.is_empty());
             self.relate(param_env, alias, variance, rigid_ctor)
@@ -796,11 +795,8 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         rhs: T,
     ) -> Result<(), NoSolution> {
         let cause = ObligationCause::dummy();
-        let InferOk { value: (), obligations } = self
-            .infcx
-            .at(&cause, param_env)
-            .trace(lhs, rhs)
-            .eq_structurally_relating_aliases(lhs, rhs)?;
+        let InferOk { value: (), obligations } =
+            self.infcx.at(&cause, param_env).eq_structurally_relating_aliases(lhs, rhs)?;
         assert!(obligations.is_empty());
         Ok(())
     }

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -566,10 +566,13 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                             {
                                 if let Ok(new_obligations) = infcx
                                     .at(&obligation.cause, obligation.param_env)
-                                    .trace(c1, c2)
                                     // Can define opaque types as this is only reachable with
                                     // `generic_const_exprs`
-                                    .eq(DefineOpaqueTypes::Yes, a.args, b.args)
+                                    .eq(
+                                        DefineOpaqueTypes::Yes,
+                                        ty::AliasTerm::from(a),
+                                        ty::AliasTerm::from(b),
+                                    )
                                 {
                                     return ProcessResult::Changed(mk_pending(
                                         new_obligations.into_obligations(),

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -910,10 +910,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                 if let Ok(InferOk { obligations, value: () }) = self
                                     .infcx
                                     .at(&obligation.cause, obligation.param_env)
-                                    .trace(c1, c2)
                                     // Can define opaque types as this is only reachable with
                                     // `generic_const_exprs`
-                                    .eq(DefineOpaqueTypes::Yes, a.args, b.args)
+                                    .eq(
+                                        DefineOpaqueTypes::Yes,
+                                        ty::AliasTerm::from(a),
+                                        ty::AliasTerm::from(b),
+                                    )
                                 {
                                     return self.evaluate_predicates_recursively(
                                         previous_stack,