Rollup merge of #135367 - Urgau:unreach_pub-std-3, r=Noratrieb

Enable `unreachable_pub` lint in `alloc`

This PR enables the [`unreachable_pub`](https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#unreachable-pub) lint as warn in the `alloc` crate.

Most of changes are in the btree implementation and in tests.

*The diff was mostly generated with `./x.py fix --stage 1 library/alloc/ -- --broken-code`, as well as manual edits for code in macros and in tests.*

Continuation of #134286 and #135366

r? libs

21 files changed, 251 insertions, 210 deletions

diff --git a/library/alloc/src/collections/btree/append.rs b/library/alloc/src/collections/btree/append.rs
index d137d2721ee..091376d5d68 100644
--- a/library/alloc/src/collections/btree/append.rs
+++ b/library/alloc/src/collections/btree/append.rs
@@ -16,7 +16,7 @@ impl<K, V> Root<K, V> {
     /// a `BTreeMap`, both iterators should produce keys in strictly ascending
     /// order, each greater than all keys in the tree, including any keys
     /// already in the tree upon entry.
-    pub fn append_from_sorted_iters<I, A: Allocator + Clone>(
+    pub(super) fn append_from_sorted_iters<I, A: Allocator + Clone>(
         &mut self,
         left: I,
         right: I,
@@ -36,8 +36,12 @@ impl<K, V> Root<K, V> {
     /// Pushes all key-value pairs to the end of the tree, incrementing a
     /// `length` variable along the way. The latter makes it easier for the
     /// caller to avoid a leak when the iterator panicks.
-    pub fn bulk_push<I, A: Allocator + Clone>(&mut self, iter: I, length: &mut usize, alloc: A)
-    where
+    pub(super) fn bulk_push<I, A: Allocator + Clone>(
+        &mut self,
+        iter: I,
+        length: &mut usize,
+        alloc: A,
+    ) where
         I: Iterator<Item = (K, V)>,
     {
         let mut cur_node = self.borrow_mut().last_leaf_edge().into_node();
diff --git a/library/alloc/src/collections/btree/borrow.rs b/library/alloc/src/collections/btree/borrow.rs
index 000b9bd0fab..e848ac3f2d1 100644
--- a/library/alloc/src/collections/btree/borrow.rs
+++ b/library/alloc/src/collections/btree/borrow.rs
@@ -11,7 +11,7 @@ use core::ptr::NonNull;
 /// the compiler to follow. A `DormantMutRef` allows you to check borrowing
 /// yourself, while still expressing its stacked nature, and encapsulating
 /// the raw pointer code needed to do this without undefined behavior.
-pub struct DormantMutRef<'a, T> {
+pub(super) struct DormantMutRef<'a, T> {
     ptr: NonNull<T>,
     _marker: PhantomData<&'a mut T>,
 }
@@ -23,7 +23,7 @@ impl<'a, T> DormantMutRef<'a, T> {
     /// Capture a unique borrow, and immediately reborrow it. For the compiler,
     /// the lifetime of the new reference is the same as the lifetime of the
     /// original reference, but you promise to use it for a shorter period.
-    pub fn new(t: &'a mut T) -> (&'a mut T, Self) {
+    pub(super) fn new(t: &'a mut T) -> (&'a mut T, Self) {
         let ptr = NonNull::from(t);
         // SAFETY: we hold the borrow throughout 'a via `_marker`, and we expose
         // only this reference, so it is unique.
@@ -37,7 +37,7 @@ impl<'a, T> DormantMutRef<'a, T> {
     ///
     /// The reborrow must have ended, i.e., the reference returned by `new` and
     /// all pointers and references derived from it, must not be used anymore.
-    pub unsafe fn awaken(self) -> &'a mut T {
+    pub(super) unsafe fn awaken(self) -> &'a mut T {
         // SAFETY: our own safety conditions imply this reference is again unique.
         unsafe { &mut *self.ptr.as_ptr() }
     }
@@ -48,7 +48,7 @@ impl<'a, T> DormantMutRef<'a, T> {
     ///
     /// The reborrow must have ended, i.e., the reference returned by `new` and
     /// all pointers and references derived from it, must not be used anymore.
-    pub unsafe fn reborrow(&mut self) -> &'a mut T {
+    pub(super) unsafe fn reborrow(&mut self) -> &'a mut T {
         // SAFETY: our own safety conditions imply this reference is again unique.
         unsafe { &mut *self.ptr.as_ptr() }
     }
@@ -59,7 +59,7 @@ impl<'a, T> DormantMutRef<'a, T> {
     ///
     /// The reborrow must have ended, i.e., the reference returned by `new` and
     /// all pointers and references derived from it, must not be used anymore.
-    pub unsafe fn reborrow_shared(&self) -> &'a T {
+    pub(super) unsafe fn reborrow_shared(&self) -> &'a T {
         // SAFETY: our own safety conditions imply this reference is again unique.
         unsafe { &*self.ptr.as_ptr() }
     }
diff --git a/library/alloc/src/collections/btree/dedup_sorted_iter.rs b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
index cd6a88f3291..6bcf0bca519 100644
--- a/library/alloc/src/collections/btree/dedup_sorted_iter.rs
+++ b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
@@ -6,7 +6,7 @@ use core::iter::Peekable;
 /// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].
 ///
 /// [1]: crate::collections::BTreeMap::bulk_build_from_sorted_iter
-pub struct DedupSortedIter<K, V, I>
+pub(super) struct DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,
 {
@@ -17,7 +17,7 @@ impl<K, V, I> DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,
 {
-    pub fn new(iter: I) -> Self {
+    pub(super) fn new(iter: I) -> Self {
         Self { iter: iter.peekable() }
     }
 }
diff --git a/library/alloc/src/collections/btree/fix.rs b/library/alloc/src/collections/btree/fix.rs
index 09edea3555a..b0c67597946 100644
--- a/library/alloc/src/collections/btree/fix.rs
+++ b/library/alloc/src/collections/btree/fix.rs
@@ -57,7 +57,10 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     ///
     /// This method does not expect ancestors to already be underfull upon entry
     /// and panics if it encounters an empty ancestor.
-    pub fn fix_node_and_affected_ancestors<A: Allocator + Clone>(mut self, alloc: A) -> bool {
+    pub(super) fn fix_node_and_affected_ancestors<A: Allocator + Clone>(
+        mut self,
+        alloc: A,
+    ) -> bool {
         loop {
             match self.fix_node_through_parent(alloc.clone()) {
                 Ok(Some(parent)) => self = parent.forget_type(),
@@ -70,7 +73,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
 
 impl<K, V> Root<K, V> {
     /// Removes empty levels on the top, but keeps an empty leaf if the entire tree is empty.
-    pub fn fix_top<A: Allocator + Clone>(&mut self, alloc: A) {
+    pub(super) fn fix_top<A: Allocator + Clone>(&mut self, alloc: A) {
         while self.height() > 0 && self.len() == 0 {
             self.pop_internal_level(alloc.clone());
         }
@@ -79,7 +82,7 @@ impl<K, V> Root<K, V> {
     /// Stocks up or merge away any underfull nodes on the right border of the
     /// tree. The other nodes, those that are not the root nor a rightmost edge,
     /// must already have at least MIN_LEN elements.
-    pub fn fix_right_border<A: Allocator + Clone>(&mut self, alloc: A) {
+    pub(super) fn fix_right_border<A: Allocator + Clone>(&mut self, alloc: A) {
         self.fix_top(alloc.clone());
         if self.len() > 0 {
             self.borrow_mut().last_kv().fix_right_border_of_right_edge(alloc.clone());
@@ -88,7 +91,7 @@ impl<K, V> Root<K, V> {
     }
 
     /// The symmetric clone of `fix_right_border`.
-    pub fn fix_left_border<A: Allocator + Clone>(&mut self, alloc: A) {
+    pub(super) fn fix_left_border<A: Allocator + Clone>(&mut self, alloc: A) {
         self.fix_top(alloc.clone());
         if self.len() > 0 {
             self.borrow_mut().first_kv().fix_left_border_of_left_edge(alloc.clone());
@@ -99,7 +102,7 @@ impl<K, V> Root<K, V> {
     /// Stocks up any underfull nodes on the right border of the tree.
     /// The other nodes, those that are neither the root nor a rightmost edge,
     /// must be prepared to have up to MIN_LEN elements stolen.
-    pub fn fix_right_border_of_plentiful(&mut self) {
+    pub(super) fn fix_right_border_of_plentiful(&mut self) {
         let mut cur_node = self.borrow_mut();
         while let Internal(internal) = cur_node.force() {
             // Check if rightmost child is underfull.
diff --git a/library/alloc/src/collections/btree/mem.rs b/library/alloc/src/collections/btree/mem.rs
index d738c5c47b4..4643c4133d5 100644
--- a/library/alloc/src/collections/btree/mem.rs
+++ b/library/alloc/src/collections/btree/mem.rs
@@ -6,7 +6,7 @@ use core::{intrinsics, mem, ptr};
 /// If a panic occurs in the `change` closure, the entire process will be aborted.
 #[allow(dead_code)] // keep as illustration and for future use
 #[inline]
-pub fn take_mut<T>(v: &mut T, change: impl FnOnce(T) -> T) {
+pub(super) fn take_mut<T>(v: &mut T, change: impl FnOnce(T) -> T) {
     replace(v, |value| (change(value), ()))
 }
 
@@ -15,7 +15,7 @@ pub fn take_mut<T>(v: &mut T, change: impl FnOnce(T) -> T) {
 ///
 /// If a panic occurs in the `change` closure, the entire process will be aborted.
 #[inline]
-pub fn replace<T, R>(v: &mut T, change: impl FnOnce(T) -> (T, R)) -> R {
+pub(super) fn replace<T, R>(v: &mut T, change: impl FnOnce(T) -> (T, R)) -> R {
     struct PanicGuard;
     impl Drop for PanicGuard {
         fn drop(&mut self) {
diff --git a/library/alloc/src/collections/btree/merge_iter.rs b/library/alloc/src/collections/btree/merge_iter.rs
index 7f23d93b990..c5b93d30a11 100644
--- a/library/alloc/src/collections/btree/merge_iter.rs
+++ b/library/alloc/src/collections/btree/merge_iter.rs
@@ -4,7 +4,7 @@ use core::iter::FusedIterator;
 
 /// Core of an iterator that merges the output of two strictly ascending iterators,
 /// for instance a union or a symmetric difference.
-pub struct MergeIterInner<I: Iterator> {
+pub(super) struct MergeIterInner<I: Iterator> {
     a: I,
     b: I,
     peeked: Option<Peeked<I>>,
@@ -40,7 +40,7 @@ where
 
 impl<I: Iterator> MergeIterInner<I> {
     /// Creates a new core for an iterator merging a pair of sources.
-    pub fn new(a: I, b: I) -> Self {
+    pub(super) fn new(a: I, b: I) -> Self {
         MergeIterInner { a, b, peeked: None }
     }
 
@@ -51,7 +51,7 @@ impl<I: Iterator> MergeIterInner<I> {
     /// the sources are not strictly ascending). If neither returned option
     /// contains a value, iteration has finished and subsequent calls will
     /// return the same empty pair.
-    pub fn nexts<Cmp: Fn(&I::Item, &I::Item) -> Ordering>(
+    pub(super) fn nexts<Cmp: Fn(&I::Item, &I::Item) -> Ordering>(
         &mut self,
         cmp: Cmp,
     ) -> (Option<I::Item>, Option<I::Item>)
@@ -85,7 +85,7 @@ impl<I: Iterator> MergeIterInner<I> {
     }
 
     /// Returns a pair of upper bounds for the `size_hint` of the final iterator.
-    pub fn lens(&self) -> (usize, usize)
+    pub(super) fn lens(&self) -> (usize, usize)
     where
         I: ExactSizeIterator,
     {
diff --git a/library/alloc/src/collections/btree/mod.rs b/library/alloc/src/collections/btree/mod.rs
index b8667d09c33..66514806673 100644
--- a/library/alloc/src/collections/btree/mod.rs
+++ b/library/alloc/src/collections/btree/mod.rs
@@ -2,13 +2,13 @@ mod append;
 mod borrow;
 mod dedup_sorted_iter;
 mod fix;
-pub mod map;
+pub(super) mod map;
 mod mem;
 mod merge_iter;
 mod navigate;
 mod node;
 mod remove;
 mod search;
-pub mod set;
+pub(super) mod set;
 mod set_val;
 mod split;
diff --git a/library/alloc/src/collections/btree/navigate.rs b/library/alloc/src/collections/btree/navigate.rs
index 14b7d4ad71f..b2a7de74875 100644
--- a/library/alloc/src/collections/btree/navigate.rs
+++ b/library/alloc/src/collections/btree/navigate.rs
@@ -7,7 +7,7 @@ use super::node::{Handle, NodeRef, marker};
 use super::search::SearchBound;
 use crate::alloc::Allocator;
 // `front` and `back` are always both `None` or both `Some`.
-pub struct LeafRange<BorrowType, K, V> {
+pub(super) struct LeafRange<BorrowType, K, V> {
     front: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
     back: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
 }
@@ -25,7 +25,7 @@ impl<B, K, V> Default for LeafRange<B, K, V> {
 }
 
 impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
-    pub fn none() -> Self {
+    pub(super) fn none() -> Self {
         LeafRange { front: None, back: None }
     }
 
@@ -34,7 +34,7 @@ impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
     }
 
     /// Temporarily takes out another, immutable equivalent of the same range.
-    pub fn reborrow(&self) -> LeafRange<marker::Immut<'_>, K, V> {
+    pub(super) fn reborrow(&self) -> LeafRange<marker::Immut<'_>, K, V> {
         LeafRange {
             front: self.front.as_ref().map(|f| f.reborrow()),
             back: self.back.as_ref().map(|b| b.reborrow()),
@@ -44,24 +44,24 @@ impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
 
 impl<'a, K, V> LeafRange<marker::Immut<'a>, K, V> {
     #[inline]
-    pub fn next_checked(&mut self) -> Option<(&'a K, &'a V)> {
+    pub(super) fn next_checked(&mut self) -> Option<(&'a K, &'a V)> {
         self.perform_next_checked(|kv| kv.into_kv())
     }
 
     #[inline]
-    pub fn next_back_checked(&mut self) -> Option<(&'a K, &'a V)> {
+    pub(super) fn next_back_checked(&mut self) -> Option<(&'a K, &'a V)> {
         self.perform_next_back_checked(|kv| kv.into_kv())
     }
 }
 
 impl<'a, K, V> LeafRange<marker::ValMut<'a>, K, V> {
     #[inline]
-    pub fn next_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
+    pub(super) fn next_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
         self.perform_next_checked(|kv| unsafe { ptr::read(kv) }.into_kv_valmut())
     }
 
     #[inline]
-    pub fn next_back_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
+    pub(super) fn next_back_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
         self.perform_next_back_checked(|kv| unsafe { ptr::read(kv) }.into_kv_valmut())
     }
 }
@@ -124,7 +124,7 @@ impl<BorrowType, K, V> LazyLeafHandle<BorrowType, K, V> {
 }
 
 // `front` and `back` are always both `None` or both `Some`.
-pub struct LazyLeafRange<BorrowType, K, V> {
+pub(super) struct LazyLeafRange<BorrowType, K, V> {
     front: Option<LazyLeafHandle<BorrowType, K, V>>,
     back: Option<LazyLeafHandle<BorrowType, K, V>>,
 }
@@ -142,12 +142,12 @@ impl<'a, K: 'a, V: 'a> Clone for LazyLeafRange<marker::Immut<'a>, K, V> {
 }
 
 impl<BorrowType, K, V> LazyLeafRange<BorrowType, K, V> {
-    pub fn none() -> Self {
+    pub(super) fn none() -> Self {
         LazyLeafRange { front: None, back: None }
     }
 
     /// Temporarily takes out another, immutable equivalent of the same range.
-    pub fn reborrow(&self) -> LazyLeafRange<marker::Immut<'_>, K, V> {
+    pub(super) fn reborrow(&self) -> LazyLeafRange<marker::Immut<'_>, K, V> {
         LazyLeafRange {
             front: self.front.as_ref().map(|f| f.reborrow()),
             back: self.back.as_ref().map(|b| b.reborrow()),
@@ -157,24 +157,24 @@ impl<BorrowType, K, V> LazyLeafRange<BorrowType, K, V> {
 
 impl<'a, K, V> LazyLeafRange<marker::Immut<'a>, K, V> {
     #[inline]
-    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
+    pub(super) unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
         unsafe { self.init_front().unwrap().next_unchecked() }
     }
 
     #[inline]
-    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
+    pub(super) unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
         unsafe { self.init_back().unwrap().next_back_unchecked() }
     }
 }
 
 impl<'a, K, V> LazyLeafRange<marker::ValMut<'a>, K, V> {
     #[inline]
-    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
+    pub(super) unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
         unsafe { self.init_front().unwrap().next_unchecked() }
     }
 
     #[inline]
-    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
+    pub(super) unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
         unsafe { self.init_back().unwrap().next_back_unchecked() }
     }
 }
@@ -190,7 +190,7 @@ impl<K, V> LazyLeafRange<marker::Dying, K, V> {
     }
 
     #[inline]
-    pub unsafe fn deallocating_next_unchecked<A: Allocator + Clone>(
+    pub(super) unsafe fn deallocating_next_unchecked<A: Allocator + Clone>(
         &mut self,
         alloc: A,
     ) -> Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV> {
@@ -200,7 +200,7 @@ impl<K, V> LazyLeafRange<marker::Dying, K, V> {
     }
 
     #[inline]
-    pub unsafe fn deallocating_next_back_unchecked<A: Allocator + Clone>(
+    pub(super) unsafe fn deallocating_next_back_unchecked<A: Allocator + Clone>(
         &mut self,
         alloc: A,
     ) -> Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV> {
@@ -210,7 +210,7 @@ impl<K, V> LazyLeafRange<marker::Dying, K, V> {
     }
 
     #[inline]
-    pub fn deallocating_end<A: Allocator + Clone>(&mut self, alloc: A) {
+    pub(super) fn deallocating_end<A: Allocator + Clone>(&mut self, alloc: A) {
         if let Some(front) = self.take_front() {
             front.deallocating_end(alloc)
         }
@@ -313,7 +313,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
     ///
     /// The result is meaningful only if the tree is ordered by key, like the tree
     /// in a `BTreeMap` is.
-    pub fn range_search<Q, R>(self, range: R) -> LeafRange<marker::Immut<'a>, K, V>
+    pub(super) fn range_search<Q, R>(self, range: R) -> LeafRange<marker::Immut<'a>, K, V>
     where
         Q: ?Sized + Ord,
         K: Borrow<Q>,
@@ -324,7 +324,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
     }
 
     /// Finds the pair of leaf edges delimiting an entire tree.
-    pub fn full_range(self) -> LazyLeafRange<marker::Immut<'a>, K, V> {
+    pub(super) fn full_range(self) -> LazyLeafRange<marker::Immut<'a>, K, V> {
         full_range(self, self)
     }
 }
@@ -339,7 +339,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::ValMut<'a>, K, V, marker::LeafOrInternal>
     ///
     /// # Safety
     /// Do not use the duplicate handles to visit the same KV twice.
-    pub fn range_search<Q, R>(self, range: R) -> LeafRange<marker::ValMut<'a>, K, V>
+    pub(super) fn range_search<Q, R>(self, range: R) -> LeafRange<marker::ValMut<'a>, K, V>
     where
         Q: ?Sized + Ord,
         K: Borrow<Q>,
@@ -351,7 +351,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::ValMut<'a>, K, V, marker::LeafOrInternal>
     /// Splits a unique reference into a pair of leaf edges delimiting the full range of the tree.
     /// The results are non-unique references allowing mutation (of values only), so must be used
     /// with care.
-    pub fn full_range(self) -> LazyLeafRange<marker::ValMut<'a>, K, V> {
+    pub(super) fn full_range(self) -> LazyLeafRange<marker::ValMut<'a>, K, V> {
         // We duplicate the root NodeRef here -- we will never visit the same KV
         // twice, and never end up with overlapping value references.
         let self2 = unsafe { ptr::read(&self) };
@@ -363,7 +363,7 @@ impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
     /// Splits a unique reference into a pair of leaf edges delimiting the full range of the tree.
     /// The results are non-unique references allowing massively destructive mutation, so must be
     /// used with the utmost care.
-    pub fn full_range(self) -> LazyLeafRange<marker::Dying, K, V> {
+    pub(super) fn full_range(self) -> LazyLeafRange<marker::Dying, K, V> {
         // We duplicate the root NodeRef here -- we will never access it in a way
         // that overlaps references obtained from the root.
         let self2 = unsafe { ptr::read(&self) };
@@ -377,7 +377,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
     /// on the right side, which is either in the same leaf node or in an ancestor node.
     /// If the leaf edge is the last one in the tree, returns [`Result::Err`] with the root node.
-    pub fn next_kv(
+    pub(super) fn next_kv(
         self,
     ) -> Result<
         Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
@@ -398,7 +398,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
     /// on the left side, which is either in the same leaf node or in an ancestor node.
     /// If the leaf edge is the first one in the tree, returns [`Result::Err`] with the root node.
-    pub fn next_back_kv(
+    pub(super) fn next_back_kv(
         self,
     ) -> Result<
         Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
@@ -627,7 +627,9 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     /// Returns the leftmost leaf edge in or underneath a node - in other words, the edge
     /// you need first when navigating forward (or last when navigating backward).
     #[inline]
-    pub fn first_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    pub(super) fn first_leaf_edge(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         let mut node = self;
         loop {
             match node.force() {
@@ -640,7 +642,9 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     /// Returns the rightmost leaf edge in or underneath a node - in other words, the edge
     /// you need last when navigating forward (or first when navigating backward).
     #[inline]
-    pub fn last_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    pub(super) fn last_leaf_edge(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         let mut node = self;
         loop {
             match node.force() {
@@ -651,7 +655,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     }
 }
 
-pub enum Position<BorrowType, K, V> {
+pub(super) enum Position<BorrowType, K, V> {
     Leaf(NodeRef<BorrowType, K, V, marker::Leaf>),
     Internal(NodeRef<BorrowType, K, V, marker::Internal>),
     InternalKV,
@@ -661,7 +665,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
     /// Visits leaf nodes and internal KVs in order of ascending keys, and also
     /// visits internal nodes as a whole in a depth first order, meaning that
     /// internal nodes precede their individual KVs and their child nodes.
-    pub fn visit_nodes_in_order<F>(self, mut visit: F)
+    pub(super) fn visit_nodes_in_order<F>(self, mut visit: F)
     where
         F: FnMut(Position<marker::Immut<'a>, K, V>),
     {
@@ -693,7 +697,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
     }
 
     /// Calculates the number of elements in a (sub)tree.
-    pub fn calc_length(self) -> usize {
+    pub(super) fn calc_length(self) -> usize {
         let mut result = 0;
         self.visit_nodes_in_order(|pos| match pos {
             Position::Leaf(node) => result += node.len(),
@@ -708,7 +712,9 @@ impl<BorrowType: marker::BorrowType, K, V>
     Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>
 {
     /// Returns the leaf edge closest to a KV for forward navigation.
-    pub fn next_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    pub(super) fn next_leaf_edge(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         match self.force() {
             Leaf(leaf_kv) => leaf_kv.right_edge(),
             Internal(internal_kv) => {
@@ -719,7 +725,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     }
 
     /// Returns the leaf edge closest to a KV for backward navigation.
-    pub fn next_back_leaf_edge(
+    pub(super) fn next_back_leaf_edge(
         self,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         match self.force() {
@@ -735,7 +741,7 @@ impl<BorrowType: marker::BorrowType, K, V>
 impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
     /// Returns the leaf edge corresponding to the first point at which the
     /// given bound is true.
-    pub fn lower_bound<Q: ?Sized>(
+    pub(super) fn lower_bound<Q: ?Sized>(
         self,
         mut bound: SearchBound<&Q>,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>
@@ -758,7 +764,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
 
     /// Returns the leaf edge corresponding to the last point at which the
     /// given bound is true.
-    pub fn upper_bound<Q: ?Sized>(
+    pub(super) fn upper_bound<Q: ?Sized>(
         self,
         mut bound: SearchBound<&Q>,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>
diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs
index 4057657632b..6815ac1c193 100644
--- a/library/alloc/src/collections/btree/node.rs
+++ b/library/alloc/src/collections/btree/node.rs
@@ -40,8 +40,8 @@ use crate::alloc::{Allocator, Layout};
 use crate::boxed::Box;
 
 const B: usize = 6;
-pub const CAPACITY: usize = 2 * B - 1;
-pub const MIN_LEN_AFTER_SPLIT: usize = B - 1;
+pub(super) const CAPACITY: usize = 2 * B - 1;
+pub(super) const MIN_LEN_AFTER_SPLIT: usize = B - 1;
 const KV_IDX_CENTER: usize = B - 1;
 const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
 const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
@@ -179,7 +179,7 @@ type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;
 ///   as the returned reference is used.
 ///   The methods supporting insert bend this rule by returning a raw pointer,
 ///   i.e., a reference without any lifetime.
-pub struct NodeRef<BorrowType, K, V, Type> {
+pub(super) struct NodeRef<BorrowType, K, V, Type> {
     /// The number of levels that the node and the level of leaves are apart, a
     /// constant of the node that cannot be entirely described by `Type`, and that
     /// the node itself does not store. We only need to store the height of the root
@@ -195,7 +195,7 @@ pub struct NodeRef<BorrowType, K, V, Type> {
 /// The root node of an owned tree.
 ///
 /// Note that this does not have a destructor, and must be cleaned up manually.
-pub type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
+pub(super) type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
 
 impl<'a, K: 'a, V: 'a, Type> Copy for NodeRef<marker::Immut<'a>, K, V, Type> {}
 impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
@@ -213,7 +213,7 @@ unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type>
 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Dying, K, V, Type> {}
 
 impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
-    pub fn new_leaf<A: Allocator + Clone>(alloc: A) -> Self {
+    pub(super) fn new_leaf<A: Allocator + Clone>(alloc: A) -> Self {
         Self::from_new_leaf(LeafNode::new(alloc))
     }
 
@@ -274,7 +274,7 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
     /// The number of edges is `len() + 1`.
     /// Note that, despite being safe, calling this function can have the side effect
     /// of invalidating mutable references that unsafe code has created.
-    pub fn len(&self) -> usize {
+    pub(super) fn len(&self) -> usize {
         // Crucially, we only access the `len` field here. If BorrowType is marker::ValMut,
         // there might be outstanding mutable references to values that we must not invalidate.
         unsafe { usize::from((*Self::as_leaf_ptr(self)).len) }
@@ -285,12 +285,12 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
     /// root on top, the number says at which elevation the node appears.
     /// If you picture trees with leaves on top, the number says how high
     /// the tree extends above the node.
-    pub fn height(&self) -> usize {
+    pub(super) fn height(&self) -> usize {
         self.height
     }
 
     /// Temporarily takes out another, immutable reference to the same node.
-    pub fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
+    pub(super) fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 
@@ -315,7 +315,7 @@ impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type>
     ///
     /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
     /// both, upon success, do nothing.
-    pub fn ascend(
+    pub(super) fn ascend(
         self,
     ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
         const {
@@ -335,24 +335,24 @@ impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type>
             .ok_or(self)
     }
 
-    pub fn first_edge(self) -> Handle<Self, marker::Edge> {
+    pub(super) fn first_edge(self) -> Handle<Self, marker::Edge> {
         unsafe { Handle::new_edge(self, 0) }
     }
 
-    pub fn last_edge(self) -> Handle<Self, marker::Edge> {
+    pub(super) fn last_edge(self) -> Handle<Self, marker::Edge> {
         let len = self.len();
         unsafe { Handle::new_edge(self, len) }
     }
 
     /// Note that `self` must be nonempty.
-    pub fn first_kv(self) -> Handle<Self, marker::KV> {
+    pub(super) fn first_kv(self) -> Handle<Self, marker::KV> {
         let len = self.len();
         assert!(len > 0);
         unsafe { Handle::new_kv(self, 0) }
     }
 
     /// Note that `self` must be nonempty.
-    pub fn last_kv(self) -> Handle<Self, marker::KV> {
+    pub(super) fn last_kv(self) -> Handle<Self, marker::KV> {
         let len = self.len();
         assert!(len > 0);
         unsafe { Handle::new_kv(self, len - 1) }
@@ -381,7 +381,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
     }
 
     /// Borrows a view into the keys stored in the node.
-    pub fn keys(&self) -> &[K] {
+    pub(super) fn keys(&self) -> &[K] {
         let leaf = self.into_leaf();
         unsafe { leaf.keys.get_unchecked(..usize::from(leaf.len)).assume_init_ref() }
     }
@@ -391,7 +391,7 @@ impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
     /// Similar to `ascend`, gets a reference to a node's parent node, but also
     /// deallocates the current node in the process. This is unsafe because the
     /// current node will still be accessible despite being deallocated.
-    pub unsafe fn deallocate_and_ascend<A: Allocator + Clone>(
+    pub(super) unsafe fn deallocate_and_ascend<A: Allocator + Clone>(
         self,
         alloc: A,
     ) -> Option<Handle<NodeRef<marker::Dying, K, V, marker::Internal>, marker::Edge>> {
@@ -443,7 +443,7 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
 
     /// Returns a dormant copy of this node with its lifetime erased which can
     /// be reawakened later.
-    pub fn dormant(&self) -> NodeRef<marker::DormantMut, K, V, Type> {
+    pub(super) fn dormant(&self) -> NodeRef<marker::DormantMut, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 }
@@ -455,7 +455,7 @@ impl<K, V, Type> NodeRef<marker::DormantMut, K, V, Type> {
     ///
     /// The reborrow must have ended, i.e., the reference returned by `new` and
     /// all pointers and references derived from it, must not be used anymore.
-    pub unsafe fn awaken<'a>(self) -> NodeRef<marker::Mut<'a>, K, V, Type> {
+    pub(super) unsafe fn awaken<'a>(self) -> NodeRef<marker::Mut<'a>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 }
@@ -536,7 +536,7 @@ impl<'a, K, V, Type> NodeRef<marker::ValMut<'a>, K, V, Type> {
 
 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
     /// Borrows exclusive access to the length of the node.
-    pub fn len_mut(&mut self) -> &mut u16 {
+    pub(super) fn len_mut(&mut self) -> &mut u16 {
         &mut self.as_leaf_mut().len
     }
 }
@@ -578,14 +578,14 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
 
 impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
     /// Returns a new owned tree, with its own root node that is initially empty.
-    pub fn new<A: Allocator + Clone>(alloc: A) -> Self {
+    pub(super) fn new<A: Allocator + Clone>(alloc: A) -> Self {
         NodeRef::new_leaf(alloc).forget_type()
     }
 
     /// Adds a new internal node with a single edge pointing to the previous root node,
     /// make that new node the root node, and return it. This increases the height by 1
     /// and is the opposite of `pop_internal_level`.
-    pub fn push_internal_level<A: Allocator + Clone>(
+    pub(super) fn push_internal_level<A: Allocator + Clone>(
         &mut self,
         alloc: A,
     ) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
@@ -604,7 +604,7 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
     /// it will not invalidate other handles or references to the root node.
     ///
     /// Panics if there is no internal level, i.e., if the root node is a leaf.
-    pub fn pop_internal_level<A: Allocator + Clone>(&mut self, alloc: A) {
+    pub(super) fn pop_internal_level<A: Allocator + Clone>(&mut self, alloc: A) {
         assert!(self.height > 0);
 
         let top = self.node;
@@ -628,18 +628,18 @@ impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
     /// Mutably borrows the owned root node. Unlike `reborrow_mut`, this is safe
     /// because the return value cannot be used to destroy the root, and there
     /// cannot be other references to the tree.
-    pub fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
+    pub(super) fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 
     /// Slightly mutably borrows the owned root node.
-    pub fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
+    pub(super) fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 
     /// Irreversibly transitions to a reference that permits traversal and offers
     /// destructive methods and little else.
-    pub fn into_dying(self) -> NodeRef<marker::Dying, K, V, Type> {
+    pub(super) fn into_dying(self) -> NodeRef<marker::Dying, K, V, Type> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 }
@@ -651,7 +651,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
     /// # Safety
     ///
     /// The returned handle has an unbound lifetime.
-    pub unsafe fn push_with_handle<'b>(
+    pub(super) unsafe fn push_with_handle<'b>(
         &mut self,
         key: K,
         val: V,
@@ -672,7 +672,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
 
     /// Adds a key-value pair to the end of the node, and returns
     /// the mutable reference of the inserted value.
-    pub fn push(&mut self, key: K, val: V) -> *mut V {
+    pub(super) fn push(&mut self, key: K, val: V) -> *mut V {
         // SAFETY: The unbound handle is no longer accessible.
         unsafe { self.push_with_handle(key, val).into_val_mut() }
     }
@@ -681,7 +681,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
     /// Adds a key-value pair, and an edge to go to the right of that pair,
     /// to the end of the node.
-    pub fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
+    pub(super) fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
         assert!(edge.height == self.height - 1);
 
         let len = self.len_mut();
@@ -699,21 +699,21 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
 
 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Leaf> {
     /// Removes any static information asserting that this node is a `Leaf` node.
-    pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+    pub(super) fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 }
 
 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
     /// Removes any static information asserting that this node is an `Internal` node.
-    pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+    pub(super) fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
 }
 
 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
     /// Checks whether a node is an `Internal` node or a `Leaf` node.
-    pub fn force(
+    pub(super) fn force(
         self,
     ) -> ForceResult<
         NodeRef<BorrowType, K, V, marker::Leaf>,
@@ -737,7 +737,9 @@ impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
 
 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     /// Unsafely asserts to the compiler the static information that this node is a `Leaf`.
-    pub unsafe fn cast_to_leaf_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
+    pub(super) unsafe fn cast_to_leaf_unchecked(
+        self,
+    ) -> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
         debug_assert!(self.height == 0);
         NodeRef { height: self.height, node: self.node, _marker: PhantomData }
     }
@@ -757,7 +759,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
 /// a child node, these represent the spaces where child pointers would go between the key-value
 /// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one
 /// to the left of the node, one between the two pairs, and one at the right of the node.
-pub struct Handle<Node, Type> {
+pub(super) struct Handle<Node, Type> {
     node: Node,
     idx: usize,
     _marker: PhantomData<Type>,
@@ -774,12 +776,12 @@ impl<Node: Copy, Type> Clone for Handle<Node, Type> {
 
 impl<Node, Type> Handle<Node, Type> {
     /// Retrieves the node that contains the edge or key-value pair this handle points to.
-    pub fn into_node(self) -> Node {
+    pub(super) fn into_node(self) -> Node {
         self.node
     }
 
     /// Returns the position of this handle in the node.
-    pub fn idx(&self) -> usize {
+    pub(super) fn idx(&self) -> usize {
         self.idx
     }
 }
@@ -787,17 +789,17 @@ impl<Node, Type> Handle<Node, Type> {
 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV> {
     /// Creates a new handle to a key-value pair in `node`.
     /// Unsafe because the caller must ensure that `idx < node.len()`.
-    pub unsafe fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
+    pub(super) unsafe fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
         debug_assert!(idx < node.len());
 
         Handle { node, idx, _marker: PhantomData }
     }
 
-    pub fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
+    pub(super) fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
         unsafe { Handle::new_edge(self.node, self.idx) }
     }
 
-    pub fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
+    pub(super) fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
         unsafe { Handle::new_edge(self.node, self.idx + 1) }
     }
 }
@@ -815,7 +817,9 @@ impl<BorrowType, K, V, NodeType, HandleType>
     Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
 {
     /// Temporarily takes out another immutable handle on the same location.
-    pub fn reborrow(&self) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
+    pub(super) fn reborrow(
+        &self,
+    ) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
         // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
         Handle { node: self.node.reborrow(), idx: self.idx, _marker: PhantomData }
     }
@@ -827,7 +831,7 @@ impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeT
     /// dangerous.
     ///
     /// For details, see `NodeRef::reborrow_mut`.
-    pub unsafe fn reborrow_mut(
+    pub(super) unsafe fn reborrow_mut(
         &mut self,
     ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
         // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
@@ -837,7 +841,9 @@ impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeT
     /// Returns a dormant copy of this handle which can be reawakened later.
     ///
     /// See `DormantMutRef` for more details.
-    pub fn dormant(&self) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
+    pub(super) fn dormant(
+        &self,
+    ) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
         Handle { node: self.node.dormant(), idx: self.idx, _marker: PhantomData }
     }
 }
@@ -849,7 +855,9 @@ impl<K, V, NodeType, HandleType> Handle<NodeRef<marker::DormantMut, K, V, NodeTy
     ///
     /// The reborrow must have ended, i.e., the reference returned by `new` and
     /// all pointers and references derived from it, must not be used anymore.
-    pub unsafe fn awaken<'a>(self) -> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
+    pub(super) unsafe fn awaken<'a>(
+        self,
+    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
         Handle { node: unsafe { self.node.awaken() }, idx: self.idx, _marker: PhantomData }
     }
 }
@@ -857,13 +865,15 @@ impl<K, V, NodeType, HandleType> Handle<NodeRef<marker::DormantMut, K, V, NodeTy
 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
     /// Creates a new handle to an edge in `node`.
     /// Unsafe because the caller must ensure that `idx <= node.len()`.
-    pub unsafe fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
+    pub(super) unsafe fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
         debug_assert!(idx <= node.len());
 
         Handle { node, idx, _marker: PhantomData }
     }
 
-    pub fn left_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
+    pub(super) fn left_kv(
+        self,
+    ) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
         if self.idx > 0 {
             Ok(unsafe { Handle::new_kv(self.node, self.idx - 1) })
         } else {
@@ -871,7 +881,9 @@ impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, mar
         }
     }
 
-    pub fn right_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
+    pub(super) fn right_kv(
+        self,
+    ) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
         if self.idx < self.node.len() {
             Ok(unsafe { Handle::new_kv(self.node, self.idx) })
         } else {
@@ -880,7 +892,7 @@ impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, mar
     }
 }
 
-pub enum LeftOrRight<T> {
+pub(super) enum LeftOrRight<T> {
     Left(T),
     Right(T),
 }
@@ -1034,7 +1046,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
     /// If the returned result is some `SplitResult`, the `left` field will be the root node.
     /// The returned pointer points to the inserted value, which in the case of `SplitResult`
     /// is in the `left` or `right` tree.
-    pub fn insert_recursing<A: Allocator + Clone>(
+    pub(super) fn insert_recursing<A: Allocator + Clone>(
         self,
         key: K,
         value: V,
@@ -1078,7 +1090,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     ///
     /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
     /// both, upon success, do nothing.
-    pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+    pub(super) fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
         const {
             assert!(BorrowType::TRAVERSAL_PERMIT);
         }
@@ -1097,7 +1109,7 @@ impl<BorrowType: marker::BorrowType, K, V>
 }
 
 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
-    pub fn into_kv(self) -> (&'a K, &'a V) {
+    pub(super) fn into_kv(self) -> (&'a K, &'a V) {
         debug_assert!(self.idx < self.node.len());
         let leaf = self.node.into_leaf();
         let k = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
@@ -1107,17 +1119,17 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeTyp
 }
 
 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
-    pub fn key_mut(&mut self) -> &mut K {
+    pub(super) fn key_mut(&mut self) -> &mut K {
         unsafe { self.node.key_area_mut(self.idx).assume_init_mut() }
     }
 
-    pub fn into_val_mut(self) -> &'a mut V {
+    pub(super) fn into_val_mut(self) -> &'a mut V {
         debug_assert!(self.idx < self.node.len());
         let leaf = self.node.into_leaf_mut();
         unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() }
     }
 
-    pub fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
+    pub(super) fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
         debug_assert!(self.idx < self.node.len());
         let leaf = self.node.into_leaf_mut();
         let k = unsafe { leaf.keys.get_unchecked_mut(self.idx).assume_init_mut() };
@@ -1127,13 +1139,13 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
 }
 
 impl<'a, K, V, NodeType> Handle<NodeRef<marker::ValMut<'a>, K, V, NodeType>, marker::KV> {
-    pub fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
+    pub(super) fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
         unsafe { self.node.into_key_val_mut_at(self.idx) }
     }
 }
 
 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
-    pub fn kv_mut(&mut self) -> (&mut K, &mut V) {
+    pub(super) fn kv_mut(&mut self) -> (&mut K, &mut V) {
         debug_assert!(self.idx < self.node.len());
         // We cannot call separate key and value methods, because calling the second one
         // invalidates the reference returned by the first.
@@ -1146,7 +1158,7 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
     }
 
     /// Replaces the key and value that the KV handle refers to.
-    pub fn replace_kv(&mut self, k: K, v: V) -> (K, V) {
+    pub(super) fn replace_kv(&mut self, k: K, v: V) -> (K, V) {
         let (key, val) = self.kv_mut();
         (mem::replace(key, k), mem::replace(val, v))
     }
@@ -1156,7 +1168,7 @@ impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV>
     /// Extracts the key and value that the KV handle refers to.
     /// # Safety
     /// The node that the handle refers to must not yet have been deallocated.
-    pub unsafe fn into_key_val(mut self) -> (K, V) {
+    pub(super) unsafe fn into_key_val(mut self) -> (K, V) {
         debug_assert!(self.idx < self.node.len());
         let leaf = self.node.as_leaf_dying();
         unsafe {
@@ -1170,7 +1182,7 @@ impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV>
     /// # Safety
     /// The node that the handle refers to must not yet have been deallocated.
     #[inline]
-    pub unsafe fn drop_key_val(mut self) {
+    pub(super) unsafe fn drop_key_val(mut self) {
         // Run the destructor of the value even if the destructor of the key panics.
         struct Dropper<'a, T>(&'a mut MaybeUninit<T>);
         impl<T> Drop for Dropper<'_, T> {
@@ -1229,7 +1241,10 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
     /// - The key and value pointed to by this handle are extracted.
     /// - All the key-value pairs to the right of this handle are put into a newly
     ///   allocated node.
-    pub fn split<A: Allocator + Clone>(mut self, alloc: A) -> SplitResult<'a, K, V, marker::Leaf> {
+    pub(super) fn split<A: Allocator + Clone>(
+        mut self,
+        alloc: A,
+    ) -> SplitResult<'a, K, V, marker::Leaf> {
         let mut new_node = LeafNode::new(alloc);
 
         let kv = self.split_leaf_data(&mut new_node);
@@ -1240,7 +1255,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
 
     /// Removes the key-value pair pointed to by this handle and returns it, along with the edge
     /// that the key-value pair collapsed into.
-    pub fn remove(
+    pub(super) fn remove(
         mut self,
     ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
         let old_len = self.node.len();
@@ -1261,7 +1276,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
     /// - The key and value pointed to by this handle are extracted.
     /// - All the edges and key-value pairs to the right of this handle are put into
     ///   a newly allocated node.
-    pub fn split<A: Allocator + Clone>(
+    pub(super) fn split<A: Allocator + Clone>(
         mut self,
         alloc: A,
     ) -> SplitResult<'a, K, V, marker::Internal> {
@@ -1285,14 +1300,14 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
 
 /// Represents a session for evaluating and performing a balancing operation
 /// around an internal key-value pair.
-pub struct BalancingContext<'a, K, V> {
+pub(super) struct BalancingContext<'a, K, V> {
     parent: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV>,
     left_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
     right_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
 }
 
 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
-    pub fn consider_for_balancing(self) -> BalancingContext<'a, K, V> {
+    pub(super) fn consider_for_balancing(self) -> BalancingContext<'a, K, V> {
         let self1 = unsafe { ptr::read(&self) };
         let self2 = unsafe { ptr::read(&self) };
         BalancingContext {
@@ -1318,7 +1333,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     /// typically faster, since we only need to shift the node's N elements to
     /// the right, instead of shifting at least N of the sibling's elements to
     /// the left.
-    pub fn choose_parent_kv(self) -> Result<LeftOrRight<BalancingContext<'a, K, V>>, Self> {
+    pub(super) fn choose_parent_kv(self) -> Result<LeftOrRight<BalancingContext<'a, K, V>>, Self> {
         match unsafe { ptr::read(&self) }.ascend() {
             Ok(parent_edge) => match parent_edge.left_kv() {
                 Ok(left_parent_kv) => Ok(LeftOrRight::Left(BalancingContext {
@@ -1341,25 +1356,25 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
 }
 
 impl<'a, K, V> BalancingContext<'a, K, V> {
-    pub fn left_child_len(&self) -> usize {
+    pub(super) fn left_child_len(&self) -> usize {
         self.left_child.len()
     }
 
-    pub fn right_child_len(&self) -> usize {
+    pub(super) fn right_child_len(&self) -> usize {
         self.right_child.len()
     }
 
-    pub fn into_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
+    pub(super) fn into_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         self.left_child
     }
 
-    pub fn into_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
+    pub(super) fn into_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         self.right_child
     }
 
     /// Returns whether merging is possible, i.e., whether there is enough room
     /// in a node to combine the central KV with both adjacent child nodes.
-    pub fn can_merge(&self) -> bool {
+    pub(super) fn can_merge(&self) -> bool {
         self.left_child.len() + 1 + self.right_child.len() <= CAPACITY
     }
 }
@@ -1433,7 +1448,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     /// the left child node and returns the shrunk parent node.
     ///
     /// Panics unless we `.can_merge()`.
-    pub fn merge_tracking_parent<A: Allocator + Clone>(
+    pub(super) fn merge_tracking_parent<A: Allocator + Clone>(
         self,
         alloc: A,
     ) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
@@ -1444,7 +1459,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     /// the left child node and returns that child node.
     ///
     /// Panics unless we `.can_merge()`.
-    pub fn merge_tracking_child<A: Allocator + Clone>(
+    pub(super) fn merge_tracking_child<A: Allocator + Clone>(
         self,
         alloc: A,
     ) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
@@ -1456,7 +1471,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     /// where the tracked child edge ended up,
     ///
     /// Panics unless we `.can_merge()`.
-    pub fn merge_tracking_child_edge<A: Allocator + Clone>(
+    pub(super) fn merge_tracking_child_edge<A: Allocator + Clone>(
         self,
         track_edge_idx: LeftOrRight<usize>,
         alloc: A,
@@ -1479,7 +1494,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     /// of the parent, while pushing the old parent key-value pair into the right child.
     /// Returns a handle to the edge in the right child corresponding to where the original
     /// edge specified by `track_right_edge_idx` ended up.
-    pub fn steal_left(
+    pub(super) fn steal_left(
         mut self,
         track_right_edge_idx: usize,
     ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
@@ -1491,7 +1506,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     /// of the parent, while pushing the old parent key-value pair onto the left child.
     /// Returns a handle to the edge in the left child specified by `track_left_edge_idx`,
     /// which didn't move.
-    pub fn steal_right(
+    pub(super) fn steal_right(
         mut self,
         track_left_edge_idx: usize,
     ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
@@ -1500,7 +1515,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     }
 
     /// This does stealing similar to `steal_left` but steals multiple elements at once.
-    pub fn bulk_steal_left(&mut self, count: usize) {
+    pub(super) fn bulk_steal_left(&mut self, count: usize) {
         assert!(count > 0);
         unsafe {
             let left_node = &mut self.left_child;
@@ -1563,7 +1578,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
     }
 
     /// The symmetric clone of `bulk_steal_left`.
-    pub fn bulk_steal_right(&mut self, count: usize) {
+    pub(super) fn bulk_steal_right(&mut self, count: usize) {
         assert!(count > 0);
         unsafe {
             let left_node = &mut self.left_child;
@@ -1628,7 +1643,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
 }
 
 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
-    pub fn forget_node_type(
+    pub(super) fn forget_node_type(
         self,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
         unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
@@ -1636,7 +1651,7 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::E
 }
 
 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
-    pub fn forget_node_type(
+    pub(super) fn forget_node_type(
         self,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
         unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
@@ -1644,7 +1659,7 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marke
 }
 
 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::KV> {
-    pub fn forget_node_type(
+    pub(super) fn forget_node_type(
         self,
     ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
         unsafe { Handle::new_kv(self.node.forget_type(), self.idx) }
@@ -1653,7 +1668,7 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::K
 
 impl<BorrowType, K, V, Type> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, Type> {
     /// Checks whether the underlying node is an `Internal` node or a `Leaf` node.
-    pub fn force(
+    pub(super) fn force(
         self,
     ) -> ForceResult<
         Handle<NodeRef<BorrowType, K, V, marker::Leaf>, Type>,
@@ -1672,7 +1687,7 @@ impl<BorrowType, K, V, Type> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInte
 
 impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, Type> {
     /// Unsafely asserts to the compiler the static information that the handle's node is a `Leaf`.
-    pub unsafe fn cast_to_leaf_unchecked(
+    pub(super) unsafe fn cast_to_leaf_unchecked(
         self,
     ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, Type> {
         let node = unsafe { self.node.cast_to_leaf_unchecked() };
@@ -1683,7 +1698,7 @@ impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInterna
 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
     /// Move the suffix after `self` from one node to another one. `right` must be empty.
     /// The first edge of `right` remains unchanged.
-    pub fn move_suffix(
+    pub(super) fn move_suffix(
         &mut self,
         right: &mut NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
     ) {
@@ -1726,13 +1741,13 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, ma
     }
 }
 
-pub enum ForceResult<Leaf, Internal> {
+pub(super) enum ForceResult<Leaf, Internal> {
     Leaf(Leaf),
     Internal(Internal),
 }
 
 /// Result of insertion, when a node needed to expand beyond its capacity.
-pub struct SplitResult<'a, K, V, NodeType> {
+pub(super) struct SplitResult<'a, K, V, NodeType> {
     // Altered node in existing tree with elements and edges that belong to the left of `kv`.
     pub left: NodeRef<marker::Mut<'a>, K, V, NodeType>,
     // Some key and value that existed before and were split off, to be inserted elsewhere.
@@ -1742,32 +1757,32 @@ pub struct SplitResult<'a, K, V, NodeType> {
 }
 
 impl<'a, K, V> SplitResult<'a, K, V, marker::Leaf> {
-    pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
+    pub(super) fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
         SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
     }
 }
 
 impl<'a, K, V> SplitResult<'a, K, V, marker::Internal> {
-    pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
+    pub(super) fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
         SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
     }
 }
 
-pub mod marker {
+pub(super) mod marker {
     use core::marker::PhantomData;
 
-    pub enum Leaf {}
-    pub enum Internal {}
-    pub enum LeafOrInternal {}
+    pub(crate) enum Leaf {}
+    pub(crate) enum Internal {}
+    pub(crate) enum LeafOrInternal {}
 
-    pub enum Owned {}
-    pub enum Dying {}
-    pub enum DormantMut {}
-    pub struct Immut<'a>(PhantomData<&'a ()>);
-    pub struct Mut<'a>(PhantomData<&'a mut ()>);
-    pub struct ValMut<'a>(PhantomData<&'a mut ()>);
+    pub(crate) enum Owned {}
+    pub(crate) enum Dying {}
+    pub(crate) enum DormantMut {}
+    pub(crate) struct Immut<'a>(PhantomData<&'a ()>);
+    pub(crate) struct Mut<'a>(PhantomData<&'a mut ()>);
+    pub(crate) struct ValMut<'a>(PhantomData<&'a mut ()>);
 
-    pub trait BorrowType {
+    pub(crate) trait BorrowType {
         /// If node references of this borrow type allow traversing to other
         /// nodes in the tree, this constant is set to `true`. It can be used
         /// for a compile-time assertion.
@@ -1786,8 +1801,8 @@ pub mod marker {
     impl<'a> BorrowType for ValMut<'a> {}
     impl BorrowType for DormantMut {}
 
-    pub enum KV {}
-    pub enum Edge {}
+    pub(crate) enum KV {}
+    pub(crate) enum Edge {}
 }
 
 /// Inserts a value into a slice of initialized elements followed by one uninitialized element.
diff --git a/library/alloc/src/collections/btree/node/tests.rs b/library/alloc/src/collections/btree/node/tests.rs
index 4d2fa0f0941..ecd009f11c7 100644
--- a/library/alloc/src/collections/btree/node/tests.rs
+++ b/library/alloc/src/collections/btree/node/tests.rs
@@ -6,7 +6,7 @@ use crate::string::String;
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal> {
     // Asserts that the back pointer in each reachable node points to its parent.
-    pub fn assert_back_pointers(self) {
+    pub(crate) fn assert_back_pointers(self) {
         if let ForceResult::Internal(node) = self.force() {
             for idx in 0..=node.len() {
                 let edge = unsafe { Handle::new_edge(node, idx) };
@@ -20,7 +20,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
     // Renders a multi-line display of the keys in order and in tree hierarchy,
     // picturing the tree growing sideways from its root on the left to its
     // leaves on the right.
-    pub fn dump_keys(self) -> String
+    pub(crate) fn dump_keys(self) -> String
     where
         K: Debug,
     {
diff --git a/library/alloc/src/collections/btree/remove.rs b/library/alloc/src/collections/btree/remove.rs
index 56f2824b782..9d870b86f34 100644
--- a/library/alloc/src/collections/btree/remove.rs
+++ b/library/alloc/src/collections/btree/remove.rs
@@ -10,7 +10,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInter
     /// the leaf edge corresponding to that former pair. It's possible this empties
     /// a root node that is internal, which the caller should pop from the map
     /// holding the tree. The caller should also decrement the map's length.
-    pub fn remove_kv_tracking<F: FnOnce(), A: Allocator + Clone>(
+    pub(super) fn remove_kv_tracking<F: FnOnce(), A: Allocator + Clone>(
         self,
         handle_emptied_internal_root: F,
         alloc: A,
diff --git a/library/alloc/src/collections/btree/search.rs b/library/alloc/src/collections/btree/search.rs
index 22e015edac3..96e5bf10802 100644
--- a/library/alloc/src/collections/btree/search.rs
+++ b/library/alloc/src/collections/btree/search.rs
@@ -8,7 +8,7 @@ use SearchResult::*;
 use super::node::ForceResult::*;
 use super::node::{Handle, NodeRef, marker};
 
-pub enum SearchBound<T> {
+pub(super) enum SearchBound<T> {
     /// An inclusive bound to look for, just like `Bound::Included(T)`.
     Included(T),
     /// An exclusive bound to look for, just like `Bound::Excluded(T)`.
@@ -20,7 +20,7 @@ pub enum SearchBound<T> {
 }
 
 impl<T> SearchBound<T> {
-    pub fn from_range(range_bound: Bound<T>) -> Self {
+    pub(super) fn from_range(range_bound: Bound<T>) -> Self {
         match range_bound {
             Bound::Included(t) => Included(t),
             Bound::Excluded(t) => Excluded(t),
@@ -29,12 +29,12 @@ impl<T> SearchBound<T> {
     }
 }
 
-pub enum SearchResult<BorrowType, K, V, FoundType, GoDownType> {
+pub(super) enum SearchResult<BorrowType, K, V, FoundType, GoDownType> {
     Found(Handle<NodeRef<BorrowType, K, V, FoundType>, marker::KV>),
     GoDown(Handle<NodeRef<BorrowType, K, V, GoDownType>, marker::Edge>),
 }
 
-pub enum IndexResult {
+pub(super) enum IndexResult {
     KV(usize),
     Edge(usize),
 }
@@ -46,7 +46,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     ///
     /// The result is meaningful only if the tree is ordered by key, like the tree
     /// in a `BTreeMap` is.
-    pub fn search_tree<Q: ?Sized>(
+    pub(super) fn search_tree<Q: ?Sized>(
         mut self,
         key: &Q,
     ) -> SearchResult<BorrowType, K, V, marker::LeafOrInternal, marker::Leaf>
@@ -80,7 +80,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     /// As a diagnostic service, panics if the range specifies impossible bounds.
     ///
     /// The result is meaningful only if the tree is ordered by key.
-    pub fn search_tree_for_bifurcation<'r, Q: ?Sized, R>(
+    pub(super) fn search_tree_for_bifurcation<'r, Q: ?Sized, R>(
         mut self,
         range: &'r R,
     ) -> Result<
@@ -156,7 +156,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     /// the matching child node, if `self` is an internal node.
     ///
     /// The result is meaningful only if the tree is ordered by key.
-    pub fn find_lower_bound_edge<'r, Q>(
+    pub(super) fn find_lower_bound_edge<'r, Q>(
         self,
         bound: SearchBound<&'r Q>,
     ) -> (Handle<Self, marker::Edge>, SearchBound<&'r Q>)
@@ -170,7 +170,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     }
 
     /// Clone of `find_lower_bound_edge` for the upper bound.
-    pub fn find_upper_bound_edge<'r, Q>(
+    pub(super) fn find_upper_bound_edge<'r, Q>(
         self,
         bound: SearchBound<&'r Q>,
     ) -> (Handle<Self, marker::Edge>, SearchBound<&'r Q>)
@@ -192,7 +192,10 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
     ///
     /// The result is meaningful only if the tree is ordered by key, like the tree
     /// in a `BTreeMap` is.
-    pub fn search_node<Q: ?Sized>(self, key: &Q) -> SearchResult<BorrowType, K, V, Type, Type>
+    pub(super) fn search_node<Q: ?Sized>(
+        self,
+        key: &Q,
+    ) -> SearchResult<BorrowType, K, V, Type, Type>
     where
         Q: Ord,
         K: Borrow<Q>,
diff --git a/library/alloc/src/collections/btree/split.rs b/library/alloc/src/collections/btree/split.rs
index c188ed1da61..87a79e6cf3f 100644
--- a/library/alloc/src/collections/btree/split.rs
+++ b/library/alloc/src/collections/btree/split.rs
@@ -8,7 +8,7 @@ use super::search::SearchResult::*;
 impl<K, V> Root<K, V> {
     /// Calculates the length of both trees that result from splitting up
     /// a given number of distinct key-value pairs.
-    pub fn calc_split_length(
+    pub(super) fn calc_split_length(
         total_num: usize,
         root_a: &Root<K, V>,
         root_b: &Root<K, V>,
@@ -31,7 +31,11 @@ impl<K, V> Root<K, V> {
     /// and if the ordering of `Q` corresponds to that of `K`.
     /// If `self` respects all `BTreeMap` tree invariants, then both
     /// `self` and the returned tree will respect those invariants.
-    pub fn split_off<Q: ?Sized + Ord, A: Allocator + Clone>(&mut self, key: &Q, alloc: A) -> Self
+    pub(super) fn split_off<Q: ?Sized + Ord, A: Allocator + Clone>(
+        &mut self,
+        key: &Q,
+        alloc: A,
+    ) -> Self
     where
         K: Borrow<Q>,
     {
diff --git a/library/alloc/src/collections/linked_list/tests.rs b/library/alloc/src/collections/linked_list/tests.rs
index b7d4f8512a0..aa19239f6c5 100644
--- a/library/alloc/src/collections/linked_list/tests.rs
+++ b/library/alloc/src/collections/linked_list/tests.rs
@@ -58,7 +58,7 @@ fn list_from<T: Clone>(v: &[T]) -> LinkedList<T> {
     v.iter().cloned().collect()
 }
 
-pub fn check_links<T>(list: &LinkedList<T>) {
+fn check_links<T>(list: &LinkedList<T>) {
     unsafe {
         let mut len = 0;
         let mut last_ptr: Option<&Node<T>> = None;
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 28e4217e303..0bb7c432cc3 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -88,6 +88,7 @@
 #![allow(rustdoc::redundant_explicit_links)]
 #![warn(rustdoc::unescaped_backticks)]
 #![deny(ffi_unwind_calls)]
+#![warn(unreachable_pub)]
 //
 // Library features:
 // tidy-alphabetical-start
@@ -227,7 +228,7 @@ pub mod alloc;
 pub mod boxed;
 #[cfg(test)]
 mod boxed {
-    pub use std::boxed::Box;
+    pub(crate) use std::boxed::Box;
 }
 pub mod borrow;
 #[unstable(feature = "bstr", issue = "134915")]
diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index ad86bf4bf07..b80d1fc7889 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/library/alloc/src/raw_vec.rs
@@ -97,7 +97,7 @@ impl<T> RawVec<T, Global> {
     /// `RawVec` with capacity `usize::MAX`. Useful for implementing
     /// delayed allocation.
     #[must_use]
-    pub const fn new() -> Self {
+    pub(crate) const fn new() -> Self {
         Self::new_in(Global)
     }
 
@@ -120,7 +120,7 @@ impl<T> RawVec<T, Global> {
     #[must_use]
     #[inline]
     #[track_caller]
-    pub fn with_capacity(capacity: usize) -> Self {
+    pub(crate) fn with_capacity(capacity: usize) -> Self {
         Self { inner: RawVecInner::with_capacity(capacity, T::LAYOUT), _marker: PhantomData }
     }
 
@@ -129,7 +129,7 @@ impl<T> RawVec<T, Global> {
     #[must_use]
     #[inline]
     #[track_caller]
-    pub fn with_capacity_zeroed(capacity: usize) -> Self {
+    pub(crate) fn with_capacity_zeroed(capacity: usize) -> Self {
         Self {
             inner: RawVecInner::with_capacity_zeroed_in(capacity, Global, T::LAYOUT),
             _marker: PhantomData,
@@ -172,7 +172,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// Like `new`, but parameterized over the choice of allocator for
     /// the returned `RawVec`.
     #[inline]
-    pub const fn new_in(alloc: A) -> Self {
+    pub(crate) const fn new_in(alloc: A) -> Self {
         Self { inner: RawVecInner::new_in(alloc, align_of::<T>()), _marker: PhantomData }
     }
 
@@ -181,7 +181,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[track_caller]
-    pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
+    pub(crate) fn with_capacity_in(capacity: usize, alloc: A) -> Self {
         Self {
             inner: RawVecInner::with_capacity_in(capacity, alloc, T::LAYOUT),
             _marker: PhantomData,
@@ -191,7 +191,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// Like `try_with_capacity`, but parameterized over the choice of
     /// allocator for the returned `RawVec`.
     #[inline]
-    pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
+    pub(crate) fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
         match RawVecInner::try_with_capacity_in(capacity, alloc, T::LAYOUT) {
             Ok(inner) => Ok(Self { inner, _marker: PhantomData }),
             Err(e) => Err(e),
@@ -203,7 +203,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[track_caller]
-    pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
+    pub(crate) fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
         Self {
             inner: RawVecInner::with_capacity_zeroed_in(capacity, alloc, T::LAYOUT),
             _marker: PhantomData,
@@ -222,7 +222,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// Note, that the requested capacity and `self.capacity()` could differ, as
     /// an allocator could overallocate and return a greater memory block than requested.
-    pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
+    pub(crate) unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
         // Sanity-check one half of the safety requirement (we cannot check the other half).
         debug_assert!(
             len <= self.capacity(),
@@ -247,7 +247,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
     /// guaranteed.
     #[inline]
-    pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
+    pub(crate) unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
         // SAFETY: Precondition passed to the caller
         unsafe {
             let ptr = ptr.cast();
@@ -265,7 +265,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// See [`RawVec::from_raw_parts_in`].
     #[inline]
-    pub unsafe fn from_nonnull_in(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self {
+    pub(crate) unsafe fn from_nonnull_in(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self {
         // SAFETY: Precondition passed to the caller
         unsafe {
             let ptr = ptr.cast();
@@ -278,12 +278,12 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
     /// be careful.
     #[inline]
-    pub const fn ptr(&self) -> *mut T {
+    pub(crate) const fn ptr(&self) -> *mut T {
         self.inner.ptr()
     }
 
     #[inline]
-    pub fn non_null(&self) -> NonNull<T> {
+    pub(crate) fn non_null(&self) -> NonNull<T> {
         self.inner.non_null()
     }
 
@@ -291,13 +291,13 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// This will always be `usize::MAX` if `T` is zero-sized.
     #[inline]
-    pub const fn capacity(&self) -> usize {
+    pub(crate) const fn capacity(&self) -> usize {
         self.inner.capacity(size_of::<T>())
     }
 
     /// Returns a shared reference to the allocator backing this `RawVec`.
     #[inline]
-    pub fn allocator(&self) -> &A {
+    pub(crate) fn allocator(&self) -> &A {
         self.inner.allocator()
     }
 
@@ -323,7 +323,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[track_caller]
-    pub fn reserve(&mut self, len: usize, additional: usize) {
+    pub(crate) fn reserve(&mut self, len: usize, additional: usize) {
         self.inner.reserve(len, additional, T::LAYOUT)
     }
 
@@ -332,12 +332,16 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline(never)]
     #[track_caller]
-    pub fn grow_one(&mut self) {
+    pub(crate) fn grow_one(&mut self) {
         self.inner.grow_one(T::LAYOUT)
     }
 
     /// The same as `reserve`, but returns on errors instead of panicking or aborting.
-    pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
+    pub(crate) fn try_reserve(
+        &mut self,
+        len: usize,
+        additional: usize,
+    ) -> Result<(), TryReserveError> {
         self.inner.try_reserve(len, additional, T::LAYOUT)
     }
 
@@ -360,12 +364,12 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// Aborts on OOM.
     #[cfg(not(no_global_oom_handling))]
     #[track_caller]
-    pub fn reserve_exact(&mut self, len: usize, additional: usize) {
+    pub(crate) fn reserve_exact(&mut self, len: usize, additional: usize) {
         self.inner.reserve_exact(len, additional, T::LAYOUT)
     }
 
     /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
-    pub fn try_reserve_exact(
+    pub(crate) fn try_reserve_exact(
         &mut self,
         len: usize,
         additional: usize,
@@ -386,7 +390,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[track_caller]
     #[inline]
-    pub fn shrink_to_fit(&mut self, cap: usize) {
+    pub(crate) fn shrink_to_fit(&mut self, cap: usize) {
         self.inner.shrink_to_fit(cap, T::LAYOUT)
     }
 }
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index edc8d99f2f9..1cedead7aa2 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -85,6 +85,7 @@ use crate::vec::Vec;
 // functions are actually methods that are in `impl [T]` but not in
 // `core::slice::SliceExt` - we need to supply these functions for the
 // `test_permutations` test
+#[allow(unreachable_pub)] // cfg(test) pub above
 pub(crate) mod hack {
     use core::alloc::Allocator;
 
diff --git a/library/alloc/src/testing/crash_test.rs b/library/alloc/src/testing/crash_test.rs
index 684bac60d9a..8e00e4f41e5 100644
--- a/library/alloc/src/testing/crash_test.rs
+++ b/library/alloc/src/testing/crash_test.rs
@@ -11,7 +11,7 @@ use crate::fmt::Debug; // the `Debug` trait is the only thing we use from `crate
 /// Crash test dummies are identified and ordered by an id, so they can be used
 /// as keys in a BTreeMap.
 #[derive(Debug)]
-pub struct CrashTestDummy {
+pub(crate) struct CrashTestDummy {
     pub id: usize,
     cloned: AtomicUsize,
     dropped: AtomicUsize,
@@ -20,7 +20,7 @@ pub struct CrashTestDummy {
 
 impl CrashTestDummy {
     /// Creates a crash test dummy design. The `id` determines order and equality of instances.
-    pub fn new(id: usize) -> CrashTestDummy {
+    pub(crate) fn new(id: usize) -> CrashTestDummy {
         CrashTestDummy {
             id,
             cloned: AtomicUsize::new(0),
@@ -31,34 +31,34 @@ impl CrashTestDummy {
 
     /// Creates an instance of a crash test dummy that records what events it experiences
     /// and optionally panics.
-    pub fn spawn(&self, panic: Panic) -> Instance<'_> {
+    pub(crate) fn spawn(&self, panic: Panic) -> Instance<'_> {
         Instance { origin: self, panic }
     }
 
     /// Returns how many times instances of the dummy have been cloned.
-    pub fn cloned(&self) -> usize {
+    pub(crate) fn cloned(&self) -> usize {
         self.cloned.load(SeqCst)
     }
 
     /// Returns how many times instances of the dummy have been dropped.
-    pub fn dropped(&self) -> usize {
+    pub(crate) fn dropped(&self) -> usize {
         self.dropped.load(SeqCst)
     }
 
     /// Returns how many times instances of the dummy have had their `query` member invoked.
-    pub fn queried(&self) -> usize {
+    pub(crate) fn queried(&self) -> usize {
         self.queried.load(SeqCst)
     }
 }
 
 #[derive(Debug)]
-pub struct Instance<'a> {
+pub(crate) struct Instance<'a> {
     origin: &'a CrashTestDummy,
     panic: Panic,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum Panic {
+pub(crate) enum Panic {
     Never,
     InClone,
     InDrop,
@@ -66,12 +66,12 @@ pub enum Panic {
 }
 
 impl Instance<'_> {
-    pub fn id(&self) -> usize {
+    pub(crate) fn id(&self) -> usize {
         self.origin.id
     }
 
     /// Some anonymous query, the result of which is already given.
-    pub fn query<R>(&self, result: R) -> R {
+    pub(crate) fn query<R>(&self, result: R) -> R {
         self.origin.queried.fetch_add(1, SeqCst);
         if self.panic == Panic::InQuery {
             panic!("panic in `query`");
diff --git a/library/alloc/src/testing/mod.rs b/library/alloc/src/testing/mod.rs
index 7a094f8a595..c8457daf93e 100644
--- a/library/alloc/src/testing/mod.rs
+++ b/library/alloc/src/testing/mod.rs
@@ -1,3 +1,3 @@
-pub mod crash_test;
-pub mod ord_chaos;
-pub mod rng;
+pub(crate) mod crash_test;
+pub(crate) mod ord_chaos;
+pub(crate) mod rng;
diff --git a/library/alloc/src/testing/ord_chaos.rs b/library/alloc/src/testing/ord_chaos.rs
index 96ce7c15790..55e1ae5e3de 100644
--- a/library/alloc/src/testing/ord_chaos.rs
+++ b/library/alloc/src/testing/ord_chaos.rs
@@ -4,7 +4,7 @@ use std::ptr;
 
 // Minimal type with an `Ord` implementation violating transitivity.
 #[derive(Debug)]
-pub enum Cyclic3 {
+pub(crate) enum Cyclic3 {
     A,
     B,
     C,
@@ -37,16 +37,16 @@ impl Eq for Cyclic3 {}
 
 // Controls the ordering of values wrapped by `Governed`.
 #[derive(Debug)]
-pub struct Governor {
+pub(crate) struct Governor {
     flipped: Cell<bool>,
 }
 
 impl Governor {
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         Governor { flipped: Cell::new(false) }
     }
 
-    pub fn flip(&self) {
+    pub(crate) fn flip(&self) {
         self.flipped.set(!self.flipped.get());
     }
 }
@@ -55,7 +55,7 @@ impl Governor {
 // (assuming that `T` respects total order), but can suddenly be made to invert
 // that total order.
 #[derive(Debug)]
-pub struct Governed<'a, T>(pub T, pub &'a Governor);
+pub(crate) struct Governed<'a, T>(pub T, pub &'a Governor);
 
 impl<T: Ord> PartialOrd for Governed<'_, T> {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
diff --git a/library/alloc/src/testing/rng.rs b/library/alloc/src/testing/rng.rs
index ecf543bee03..77d3348f38a 100644
--- a/library/alloc/src/testing/rng.rs
+++ b/library/alloc/src/testing/rng.rs
@@ -1,5 +1,5 @@
 /// XorShiftRng
-pub struct DeterministicRng {
+pub(crate) struct DeterministicRng {
     count: usize,
     x: u32,
     y: u32,
@@ -8,12 +8,12 @@ pub struct DeterministicRng {
 }
 
 impl DeterministicRng {
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         DeterministicRng { count: 0, x: 0x193a6754, y: 0xa8a7d469, z: 0x97830e05, w: 0x113ba7bb }
     }
 
     /// Guarantees that each returned number is unique.
-    pub fn next(&mut self) -> u32 {
+    pub(crate) fn next(&mut self) -> u32 {
         self.count += 1;
         assert!(self.count <= 70029);
         let x = self.x;