document return value of `add_live_point`

1 files changed, 3 insertions, 0 deletions

diff --git a/src/librustc_mir/borrow_check/nll/region_infer/mod.rs b/src/librustc_mir/borrow_check/nll/region_infer/mod.rs
index c1518b28dab..c926c7432bb 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/mod.rs
@@ -208,6 +208,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     }
 
     /// Indicates that the region variable `v` is live at the point `point`.
+    ///
+    /// Returns `true` if this constraint is new and `false` is the
+    /// constraint was already present.
     pub(super) fn add_live_point(&mut self, v: RegionVid, point: Location) -> bool {
         debug!("add_live_point({:?}, {:?})", v, point);
         assert!(self.inferred_values.is_none(), "values already inferred");