Don't allow poly_select in new solver

Author: compiler-errors

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

@@ -1503,11 +1503,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     return None;
                 };
 
-                let Ok(Some(ImplSource::UserDefined(impl_data))) = SelectionContext::new(self)
-                    .poly_select(&obligation.with(
-                        self.tcx,
-                        predicate.kind().rebind(proj.projection_term.trait_ref(self.tcx)),
-                    ))
+                let trait_ref = self.enter_forall_and_leak_universe(
+                    predicate.kind().rebind(proj.projection_term.trait_ref(self.tcx)),
+                );
+                let Ok(Some(ImplSource::UserDefined(impl_data))) =
+                    SelectionContext::new(self).select(&obligation.with(self.tcx, trait_ref))
                 else {
                     return None;
                 };

compiler/rustc_trait_selection/src/solve/select.rs

@@ -5,7 +5,7 @@ use rustc_infer::traits::solve::inspect::ProbeKind;
 use rustc_infer::traits::solve::{CandidateSource, Certainty, Goal};
 use rustc_infer::traits::{
     BuiltinImplSource, ImplSource, ImplSourceUserDefinedData, Obligation, ObligationCause,
-    PolyTraitObligation, Selection, SelectionError, SelectionResult,
+    Selection, SelectionError, SelectionResult, TraitObligation,
 };
 use rustc_macros::extension;
 use rustc_middle::{bug, span_bug};
@@ -17,7 +17,7 @@ use crate::solve::inspect::{self, ProofTreeInferCtxtExt};
 impl<'tcx> InferCtxt<'tcx> {
     fn select_in_new_trait_solver(
         &self,
-        obligation: &PolyTraitObligation<'tcx>,
+        obligation: &TraitObligation<'tcx>,
     ) -> SelectionResult<'tcx, Selection<'tcx>> {
         assert!(self.next_trait_solver());
 

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

@@ -265,9 +265,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
     ) -> SelectionResult<'tcx, Selection<'tcx>> {
-        if self.infcx.next_trait_solver() {
-            return self.infcx.select_in_new_trait_solver(obligation);
-        }
+        assert!(!self.infcx.next_trait_solver());
 
         let candidate = match self.select_from_obligation(obligation) {
             Err(SelectionError::Overflow(OverflowError::Canonical)) => {
@@ -299,6 +297,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
     ) -> SelectionResult<'tcx, Selection<'tcx>> {
+        if self.infcx.next_trait_solver() {
+            return self.infcx.select_in_new_trait_solver(obligation);
+        }
+
         self.poly_select(&Obligation {
             cause: obligation.cause.clone(),
             param_env: obligation.param_env,