Keep solver region constraints in type ops

Canonical type-op queries don't include NextGen solver region constraints in their response. Run these operations locally under -Zassumptions-on-binders so borrowck gets the constraints.

Author: Dnreikronos

compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs

@@ -146,6 +146,24 @@ where
         root_def_id: LocalDefId,
         span: Span,
     ) -> Result<TypeOpOutput<'tcx, Self>, ErrorGuaranteed> {
+        // Canonical type-op queries drop NextGen solver region constraints when
+        // building `QueryResponse`. Evaluate locally so `-Zassumptions-on-binders`
+        // can attach those constraints to this `InferCtxt` and report them from
+        // borrowck instead of silently succeeding.
+        if infcx.tcx.assumptions_on_binders() {
+            if !infcx.disable_trait_solver_fast_paths()
+                && let Some(output) = Q::try_fast_path(infcx.tcx, &self)
+            {
+                return Ok(TypeOpOutput { output, constraints: None, error_info: None });
+            }
+
+            let (output, _) =
+                scrape_region_constraints(infcx, root_def_id, "fully_perform", span, |ocx| {
+                    Q::perform_locally_with_next_solver(ocx, self, span)
+                })?;
+            return Ok(output);
+        }
+
         let mut error_info = None;
         let mut region_constraints = QueryRegionConstraints::default();
 

tests/ui/assumptions_on_binders/alias_outlives.rs

@@ -23,7 +23,7 @@ where
 }
 
 fn borrowck_env_fail<'a, T: AliasHaver>()
-// FIXME: ^ this should raise an ERROR: unsatisfied lifetime constraint from -Zassumptions-on-binders
+//~^ ERROR: unsatisfied lifetime constraint from -Zassumptions-on-binders
 where
     <T as AliasHaver>::Assoc: 'a,
 {

tests/ui/assumptions_on_binders/alias_outlives.stderr

@@ -6,5 +6,16 @@ LL | const REGIONCK_ENV_FAIL<'a, T: AliasHaver>: ReqTrait<T::Assoc> = todo!()
    |
    = note: meoow :c
 
-error: aborting due to 1 previous error
+error: unsatisfied lifetime constraint from -Zassumptions-on-binders :3
+  --> $DIR/alias_outlives.rs:25:1
+   |
+LL | / fn borrowck_env_fail<'a, T: AliasHaver>()
+LL | |
+LL | | where
+LL | |     <T as AliasHaver>::Assoc: 'a,
+   | |_________________________________^
+   |
+   = note: meoow :c
+
+error: aborting due to 2 previous errors