mv compiler to compiler/

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -0,0 +1,18 @@
+use rustc_middle::ty::TyCtxt;
+
+use super::TraitEngine;
+use super::{ChalkFulfillmentContext, FulfillmentContext};
+
+pub trait TraitEngineExt<'tcx> {
+    fn new(tcx: TyCtxt<'tcx>) -> Box<Self>;
+}
+
+impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
+    fn new(tcx: TyCtxt<'tcx>) -> Box<Self> {
+        if tcx.sess.opts.debugging_opts.chalk {
+            Box::new(ChalkFulfillmentContext::new())
+        } else {
+            Box::new(FulfillmentContext::new())
+        }
+    }
+}