Auto merge of #30939 - shepmaster:btreeset-insert-return-value, r=alexcrichton

src/libcollections/btree/set.rs

@@ -453,7 +453,7 @@ pub fn is_superset(&self, other: &BTreeSet<T>) -> bool {
     ///
     /// If the set did not have a value present, `true` is returned.
     ///
-    /// If the set did have this key present, that value is returned, and the
+    /// If the set did have this key present, `false` is returned, and the
     /// entry is not updated. See the [module-level documentation] for more.
     ///
     /// [module-level documentation]: index.html#insert-and-complex-keys