add flag for disabling global cache and printing proof trees on error

compiler/rustc_trait_selection/src/solve/search_graph/mod.rs

@@ -13,6 +13,7 @@ use rustc_middle::traits::solve::{CanonicalInput, Certainty, MaybeCause, QueryRe
 use rustc_middle::ty::TyCtxt;
 use std::{collections::hash_map::Entry, mem};
 
+use super::eval_ctxt::DisableGlobalCache;
 use super::inspect::ProofTreeBuilder;
 use super::SolverMode;
 
@@ -213,7 +214,9 @@ impl<'tcx> SearchGraph<'tcx> {
         inspect: &mut ProofTreeBuilder<'tcx>,
         mut loop_body: impl FnMut(&mut Self, &mut ProofTreeBuilder<'tcx>) -> QueryResult<'tcx>,
     ) -> QueryResult<'tcx> {
-        if self.should_use_global_cache() {
+        if self.should_use_global_cache()
+            && inspect.disable_global_cache() == DisableGlobalCache::No
+        {
             if let Some(result) = tcx.new_solver_evaluation_cache.get(&canonical_input, tcx) {
                 debug!(?canonical_input, ?result, "cache hit");
                 inspect.cache_hit(CacheHit::Global);