Rollup merge of #81610 - ssomers:btree_emphasize_ord_bound, r=dtolnay

BTreeMap: make Ord bound explicit, compile-test its absence

Most `BTreeMap` and `BTreeSet` members are subject to an `Ord` bound but a fair number of methods are not. To better convey and perhaps later tune the `Ord` bound, make it stand out in individual `where` clauses, instead of once far away at the beginning of an `impl` block. This PR does not introduce or remove any bounds.

Also adds compilation test cases checking that the bound doesn't creep in unintended on the historically unbounded methods.

Author: m-ou-se

library/alloc/src/collections/btree/map.rs

@@ -460,7 +460,7 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for RangeMut<'_, K, V> {
     }
 }
 
-impl<K: Ord, V> BTreeMap<K, V> {
+impl<K, V> BTreeMap<K, V> {
     /// Makes a new, empty `BTreeMap`.
     ///
     /// Does not allocate anything on its own.
@@ -479,7 +479,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
-    pub const fn new() -> BTreeMap<K, V> {
+    pub const fn new() -> BTreeMap<K, V>
+    where
+        K: Ord,
+    {
         BTreeMap { root: None, length: 0 }
     }
 
@@ -498,7 +501,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert!(a.is_empty());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn clear(&mut self) {
+    pub fn clear(&mut self)
+    where
+        K: Ord,
+    {
         *self = BTreeMap::new();
     }
 
@@ -522,7 +528,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         let root_node = self.root.as_ref()?.reborrow();
@@ -550,7 +556,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "map_get_key_value", since = "1.40.0")]
     pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         let root_node = self.root.as_ref()?.reborrow();
@@ -578,7 +584,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.first_key_value(), Some((&1, &"b")));
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn first_key_value(&self) -> Option<(&K, &V)> {
+    pub fn first_key_value(&self) -> Option<(&K, &V)>
+    where
+        K: Ord,
+    {
         let root_node = self.root.as_ref()?.reborrow();
         root_node.first_leaf_edge().right_kv().ok().map(Handle::into_kv)
     }
@@ -604,7 +613,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(*map.get(&2).unwrap(), "b");
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> {
+    pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>>
+    where
+        K: Ord,
+    {
         let (map, dormant_map) = DormantMutRef::new(self);
         let root_node = map.root.as_mut()?.borrow_mut();
         let kv = root_node.first_leaf_edge().right_kv().ok()?;
@@ -631,7 +643,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert!(map.is_empty());
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn pop_first(&mut self) -> Option<(K, V)> {
+    pub fn pop_first(&mut self) -> Option<(K, V)>
+    where
+        K: Ord,
+    {
         self.first_entry().map(|entry| entry.remove_entry())
     }
 
@@ -652,7 +667,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.last_key_value(), Some((&2, &"a")));
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn last_key_value(&self) -> Option<(&K, &V)> {
+    pub fn last_key_value(&self) -> Option<(&K, &V)>
+    where
+        K: Ord,
+    {
         let root_node = self.root.as_ref()?.reborrow();
         root_node.last_leaf_edge().left_kv().ok().map(Handle::into_kv)
     }
@@ -678,7 +696,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(*map.get(&2).unwrap(), "last");
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> {
+    pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>>
+    where
+        K: Ord,
+    {
         let (map, dormant_map) = DormantMutRef::new(self);
         let root_node = map.root.as_mut()?.borrow_mut();
         let kv = root_node.last_leaf_edge().left_kv().ok()?;
@@ -705,7 +726,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert!(map.is_empty());
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn pop_last(&mut self) -> Option<(K, V)> {
+    pub fn pop_last(&mut self) -> Option<(K, V)>
+    where
+        K: Ord,
+    {
         self.last_entry().map(|entry| entry.remove_entry())
     }
 
@@ -729,7 +753,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         self.get(key).is_some()
@@ -758,7 +782,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         let root_node = self.root.as_mut()?.borrow_mut();
@@ -795,7 +819,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map[&37], "c");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
+    pub fn insert(&mut self, key: K, value: V) -> Option<V>
+    where
+        K: Ord,
+    {
         match self.entry(key) {
             Occupied(mut entry) => Some(entry.insert(value)),
             Vacant(entry) => {
@@ -827,7 +854,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         self.remove_entry(key).map(|(_, v)| v)
@@ -854,7 +881,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "btreemap_remove_entry", since = "1.45.0")]
     pub fn remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
         Q: Ord,
     {
         let (map, dormant_map) = DormantMutRef::new(self);
@@ -886,6 +913,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[unstable(feature = "btree_retain", issue = "79025")]
     pub fn retain<F>(&mut self, mut f: F)
     where
+        K: Ord,
         F: FnMut(&K, &mut V) -> bool,
     {
         self.drain_filter(|k, v| !f(k, v));
@@ -920,7 +948,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(a[&5], "f");
     /// ```
     #[stable(feature = "btree_append", since = "1.11.0")]
-    pub fn append(&mut self, other: &mut Self) {
+    pub fn append(&mut self, other: &mut Self)
+    where
+        K: Ord,
+    {
         // Do we have to append anything at all?
         if other.is_empty() {
             return;
@@ -971,7 +1002,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     pub fn range<T: ?Sized, R>(&self, range: R) -> Range<'_, K, V>
     where
         T: Ord,
-        K: Borrow<T>,
+        K: Borrow<T> + Ord,
         R: RangeBounds<T>,
     {
         if let Some(root) = &self.root {
@@ -1017,7 +1048,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     pub fn range_mut<T: ?Sized, R>(&mut self, range: R) -> RangeMut<'_, K, V>
     where
         T: Ord,
-        K: Borrow<T>,
+        K: Borrow<T> + Ord,
         R: RangeBounds<T>,
     {
         if let Some(root) = &mut self.root {
@@ -1048,7 +1079,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(count["a"], 3);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
+    pub fn entry(&mut self, key: K) -> Entry<'_, K, V>
+    where
+        K: Ord,
+    {
         // FIXME(@porglezomp) Avoid allocating if we don't insert
         let (map, dormant_map) = DormantMutRef::new(self);
         let root_node = Self::ensure_is_owned(&mut map.root).borrow_mut();
@@ -1092,7 +1126,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[stable(feature = "btree_split_off", since = "1.11.0")]
     pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self
     where
-        K: Borrow<Q>,
+        K: Borrow<Q> + Ord,
     {
         if self.is_empty() {
             return Self::new();
@@ -1150,12 +1184,16 @@ impl<K: Ord, V> BTreeMap<K, V> {
     #[unstable(feature = "btree_drain_filter", issue = "70530")]
     pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, K, V, F>
     where
+        K: Ord,
         F: FnMut(&K, &mut V) -> bool,
     {
         DrainFilter { pred, inner: self.drain_filter_inner() }
     }
 
-    pub(super) fn drain_filter_inner(&mut self) -> DrainFilterInner<'_, K, V> {
+    pub(super) fn drain_filter_inner(&mut self) -> DrainFilterInner<'_, K, V>
+    where
+        K: Ord,
+    {
         if let Some(root) = self.root.as_mut() {
             let (root, dormant_root) = DormantMutRef::new(root);
             let front = root.borrow_mut().first_leaf_edge();
@@ -1188,7 +1226,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// ```
     #[inline]
     #[unstable(feature = "map_into_keys_values", issue = "75294")]
-    pub fn into_keys(self) -> IntoKeys<K, V> {
+    pub fn into_keys(self) -> IntoKeys<K, V>
+    where
+        K: Ord,
+    {
         IntoKeys { inner: self.into_iter() }
     }
 
@@ -1211,7 +1252,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// ```
     #[inline]
     #[unstable(feature = "map_into_keys_values", issue = "75294")]
-    pub fn into_values(self) -> IntoValues<K, V> {
+    pub fn into_values(self) -> IntoValues<K, V>
+    where
+        K: Ord,
+    {
         IntoValues { inner: self.into_iter() }
     }
 }
@@ -1968,9 +2012,9 @@ impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<K: Ord, Q: ?Sized, V> Index<&Q> for BTreeMap<K, V>
+impl<K, Q: ?Sized, V> Index<&Q> for BTreeMap<K, V>
 where
-    K: Borrow<Q>,
+    K: Borrow<Q> + Ord,
     Q: Ord,
 {
     type Output = V;

library/alloc/src/collections/btree/map/tests.rs

@@ -1706,6 +1706,34 @@ fn test_send() {
     }
 }
 
+#[allow(dead_code)]
+fn test_ord_absence() {
+    fn map<K>(mut map: BTreeMap<K, ()>) {
+        map.is_empty();
+        map.len();
+        map.iter();
+        map.iter_mut();
+        map.keys();
+        map.values();
+        map.values_mut();
+        map.into_iter();
+    }
+
+    fn map_debug<K: Debug>(mut map: BTreeMap<K, ()>) {
+        format!("{:?}", map);
+        format!("{:?}", map.iter());
+        format!("{:?}", map.iter_mut());
+        format!("{:?}", map.keys());
+        format!("{:?}", map.values());
+        format!("{:?}", map.values_mut());
+        format!("{:?}", map.into_iter());
+    }
+
+    fn map_clone<K: Clone>(mut map: BTreeMap<K, ()>) {
+        map.clone_from(&map.clone());
+    }
+}
+
 #[allow(dead_code)]
 fn test_const() {
     const MAP: &'static BTreeMap<(), ()> = &BTreeMap::new();