implement drop elaboration

Fixes rust-lang#30380

Author: arielb1

src/librustc/infer/mod.rs

@@ -613,6 +613,24 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             value.trans_normalize(&infcx)
         })
     }
+
+    pub fn normalize_associated_type_in_env<T>(
+        self, value: &T, env: &'a ty::ParameterEnvironment<'tcx>
+    ) -> T
+        where T: TransNormalize<'tcx>
+    {
+        debug!("normalize_associated_type_in_env(t={:?})", value);
+
+        let value = self.erase_regions(value);
+
+        if !value.has_projection_types() {
+            return value;
+        }
+
+        self.infer_ctxt(None, Some(env.clone()), ProjectionMode::Any).enter(|infcx| {
+            value.trans_normalize(&infcx)
+       })
+    }
 }
 
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {

src/librustc_borrowck/borrowck/mir/dataflow/mod.rs

@@ -200,6 +200,12 @@ impl<'a, 'tcx: 'a, O> DataflowAnalysis<'a, 'tcx, O>
 
 pub struct DataflowResults<O>(DataflowState<O>) where O: BitDenotation;
 
+impl<O: BitDenotation> DataflowResults<O> {
+    pub fn sets(&self) -> &AllSets {
+        &self.0.sets
+    }
+}
+
 // FIXME: This type shouldn't be public, but the graphviz::MirWithFlowState trait
 // references it in a method signature. Look into using `pub(crate)` to address this.
 pub struct DataflowState<O: BitDenotation>