From 5a219cba9563dc869577f7b7a9e318a1565dd4da Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Fri, 20 Sep 2024 14:17:08 +0000
Subject: [PATCH] bail if there are too many non-region infer vars

---
 .../src/solve/eval_ctxt/canonical.rs                       | 7 +++++++
 tests/ui/traits/coherence-alias-hang.rs                    | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
index 5acfec3dee3..3887f9c529c 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
@@ -157,6 +157,13 @@ where
             },
         );
 
+        let num_non_region_vars = canonical.variables.iter().filter(|c| !c.is_region()).count();
+        if num_non_region_vars > self.cx().recursion_limit() {
+            return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow {
+                suggest_increasing_limit: true,
+            }));
+        }
+
         Ok(canonical)
     }
 
diff --git a/tests/ui/traits/coherence-alias-hang.rs b/tests/ui/traits/coherence-alias-hang.rs
index 37b80739589..c2b4d2e42d2 100644
--- a/tests/ui/traits/coherence-alias-hang.rs
+++ b/tests/ui/traits/coherence-alias-hang.rs
@@ -1,4 +1,6 @@
 //@ check-pass
+//@ revisions: current next
+//[next]@ compile-flags: -Znext-solver
 
 // Regression test for nalgebra hang <https://github.com/rust-lang/rust/issues/130056>.