Rollup merge of #141390 - compiler-errors:poly-select-new-solver, r=lcnr

Don't allow `poly_select` in new solver

I added a `poly_select` call in #140519, but this causes an ICE since the new solver doesn't properly handle the "instantiate binder -> recanonicalize" step in the proof tree visitor.

While we could fix the select visitor to look at the next step in proof tree, it's not really necessary. Instead, let's enforce that all callees call the non-higher-ranked `select` function in the new solver.

Fixes https://github.com/rust-lang/rust/issues/141322

r? lcnr

6 files changed, 69 insertions, 10 deletions

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 7d8c4df6341..b88040a0f98 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1501,11 +1501,11 @@ 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;
                 };
diff --git a/compiler/rustc_trait_selection/src/solve/select.rs b/compiler/rustc_trait_selection/src/solve/select.rs
index 4fdaf740287..1f3168fafb1 100644
--- a/compiler/rustc_trait_selection/src/solve/select.rs
+++ b/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());
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 44a76f6e083..f4ec528c672 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/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,
diff --git a/tests/ui/mismatched_types/hr-projection-mismatch.current.stderr b/tests/ui/mismatched_types/hr-projection-mismatch.current.stderr
new file mode 100644
index 00000000000..a2cec972e4a
--- /dev/null
+++ b/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`.
diff --git a/tests/ui/mismatched_types/hr-projection-mismatch.next.stderr b/tests/ui/mismatched_types/hr-projection-mismatch.next.stderr
new file mode 100644
index 00000000000..6ea0d43e153
--- /dev/null
+++ b/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`.
diff --git a/tests/ui/mismatched_types/hr-projection-mismatch.rs b/tests/ui/mismatched_types/hr-projection-mismatch.rs
new file mode 100644
index 00000000000..f96314a3fca
--- /dev/null
+++ b/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() {}