update comments

compiler/rustc_const_eval/src/interpret/util.rs

@@ -3,7 +3,11 @@
 use std::convert::TryInto;
 use std::ops::ControlFlow;
 
-/// Returns `true` if a used generic parameter requires substitution.
+/// Checks whether a type contains generic parameters which require substitution.
+///
+/// In case it does, returns a `TooGeneric` const eval error. Note that due to polymorphization
+/// types may be "concrete enough" even though they still contain generic parameters in
+/// case these parameters are unused.
 crate fn ensure_monomorphic_enough<'tcx, T>(tcx: TyCtxt<'tcx>, ty: T) -> InterpResult<'tcx>
 where
     T: TypeFoldable<'tcx>,

compiler/rustc_typeck/src/check/writeback.rs

@@ -43,7 +43,7 @@ pub fn resolve_type_vars_in_body(
         let item_def_id = self.tcx.hir().local_def_id(item_id);
 
         // This attribute causes us to dump some writeback information
-        // in the form of errors, which is uSymbol for unit tests.
+        // in the form of errors, which is used for unit tests.
         let rustc_dump_user_substs =
             self.tcx.has_attr(item_def_id.to_def_id(), sym::rustc_dump_user_substs);