Rollup merge of #133323 - compiler-errors:bail-if-self-var, r=lcnr

Bail in effects in old solver if self ty is ty var

Otherwise when we try to check something like `?t: ~const Trait` we'll immediately stick it to the first param-env candidate, lol.

r? lcnr

compiler/rustc_trait_selection/src/traits/effects.rs

@@ -27,6 +27,11 @@ pub fn evaluate_host_effect_obligation<'tcx>(
         );
     }
 
+    // Force ambiguity for infer self ty.
+    if obligation.predicate.self_ty().is_ty_var() {
+        return Err(EvaluationFailure::Ambiguous);
+    }
+
     match evaluate_host_effect_from_bounds(selcx, obligation) {
         Ok(result) => return Ok(result),
         Err(EvaluationFailure::Ambiguous) => return Err(EvaluationFailure::Ambiguous),