[Experiment] Crater run with -Ztrait-solver=next-coherence

compiler/rustc_interface/src/tests.rs

@@ -845,7 +845,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(thir_unsafeck, true);
     tracked!(tiny_const_eval_limit, true);
     tracked!(tls_model, Some(TlsModel::GeneralDynamic));
-    tracked!(trait_solver, TraitSolver::NextCoherence);
+    tracked!(trait_solver, TraitSolver::Next);
     tracked!(translate_remapped_path_to_local_path, false);
     tracked!(trap_unreachable, Some(false));
     tracked!(treat_err_as_bug, NonZeroUsize::new(1));

compiler/rustc_session/src/options.rs

@@ -992,7 +992,7 @@ mod parse {
             Some("next") => *slot = TraitSolver::Next,
             Some("next-coherence") => *slot = TraitSolver::NextCoherence,
             // default trait solver is subject to change..
-            Some("default") => *slot = TraitSolver::Classic,
+            Some("default") => *slot = TraitSolver::NextCoherence,
             _ => return false,
         }
         true
@@ -1847,8 +1847,8 @@ written to standard error output)"),
         "for every macro invocation, print its name and arguments (default: no)"),
     track_diagnostics: bool = (false, parse_bool, [UNTRACKED],
         "tracks where in rustc a diagnostic was emitted"),
-    trait_solver: TraitSolver = (TraitSolver::Classic, parse_trait_solver, [TRACKED],
-        "specify the trait solver mode used by rustc (default: classic)"),
+    trait_solver: TraitSolver = (TraitSolver::NextCoherence, parse_trait_solver, [TRACKED],
+        "specify the trait solver mode used by rustc (default: next-coherence)"),
     // Diagnostics are considered side-effects of a query (see `QuerySideEffects`) and are saved
     // alongside query results and changes to translation options can affect diagnostics - so
     // translation options should be tracked.

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -373,6 +373,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
             && has_changed
             && is_normalizes_to_hack == IsNormalizesToHack::No
             && !self.search_graph.in_cycle()
+            && false
         {
             debug!("rerunning goal to check result is stable");
             let (_orig_values, canonical_goal) = self.canonicalize_goal(goal);

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -89,7 +89,12 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
         let mut errors = Vec::new();
         for i in 0.. {
             if !infcx.tcx.recursion_limit().value_within_limit(i) {
-                unimplemented!("overflowed on pending obligations: {:?}", self.obligations);
+                let obligation = self.obligations.first().cloned().unwrap();
+                return vec![FulfillmentError {
+                    root_obligation: obligation.clone(),
+                    obligation,
+                    code: FulfillmentErrorCode::CodeAmbiguity { overflow: true },
+                }];
             }
 
             let mut has_changed = false;