Don't allow poly_select in new solver

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,

tests/ui/mismatched_types/hr-projection-mismatch.current.stderr

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/hr-projection-mismatch.rs:20:5
+   |
+LL |     wrap::<_, Thing>();
+   |     ^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected reference `&'a _`
+              found reference `&_`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/mismatched_types/hr-projection-mismatch.next.stderr

@@ -0,0 +1,20 @@
+error[E0271]: type mismatch resolving `<Thing as Trait<'a>>::Assoc == &i32`
+  --> $DIR/hr-projection-mismatch.rs:20:15
+   |
+LL |     wrap::<_, Thing>();
+   |               ^^^^^ type mismatch resolving `<Thing as Trait<'a>>::Assoc == &i32`
+   |
+note: types differ
+  --> $DIR/hr-projection-mismatch.rs:14:18
+   |
+LL |     type Assoc = &'a i32;
+   |                  ^^^^^^^
+note: required by a bound in `wrap`
+  --> $DIR/hr-projection-mismatch.rs:17:33
+   |
+LL | fn wrap<T, U: for<'a> Trait<'a, Assoc = T>>() {}
+   |                                 ^^^^^^^^^ required by this bound in `wrap`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0271`.

tests/ui/mismatched_types/hr-projection-mismatch.rs

@@ -0,0 +1,25 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// Regression test for <https://github.com/rust-lang/rust/issues/141322>.
+
+trait Trait<'a> {
+    type Assoc;
+}
+
+struct Thing;
+
+impl<'a> Trait<'a> for Thing {
+    type Assoc = &'a i32;
+}
+
+fn wrap<T, U: for<'a> Trait<'a, Assoc = T>>() {}
+
+fn foo() {
+    wrap::<_, Thing>();
+    //[next]~^ ERROR type mismatch resolving `<Thing as Trait<'a>>::Assoc == &i32
+    //[current]~^^ ERROR mismatched types
+}
+
+fn main() {}