From f606127be52016904ac7f770e443cb634c9cea34 Mon Sep 17 00:00:00 2001
From: Maybe Waffle <waffle.lapkin@gmail.com>
Date: Sat, 1 Oct 2022 22:26:48 +0000
Subject: [PATCH 1/2] make tidy accept multi-line `rustc_const_unstable`
 attributes

---
 src/tools/tidy/src/features.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/tools/tidy/src/features.rs b/src/tools/tidy/src/features.rs
index 28a0700a64b..d8b3903b98e 100644
--- a/src/tools/tidy/src/features.rs
+++ b/src/tools/tidy/src/features.rs
@@ -538,7 +538,9 @@ fn map_lib_features(
                 becoming_feature = None;
                 if line.contains("rustc_const_unstable(") {
                     // `const fn` features are handled specially.
-                    let feature_name = match find_attr_val(line, "feature") {
+                    let feature_name = match find_attr_val(line, "feature").or_else(|| {
+                        iter_lines.peek().and_then(|next| find_attr_val(next.1, "feature"))
+                    }) {
                         Some(name) => name,
                         None => err!("malformed stability attribute: missing `feature` key"),
                     };

From da78c1fd43c39166e09dd4b5cf93a66396841c2d Mon Sep 17 00:00:00 2001
From: Maybe Waffle <waffle.lapkin@gmail.com>
Date: Sat, 1 Oct 2022 22:40:04 +0000
Subject: [PATCH 2/2] Make `feature(const_btree_len)` implied by
 `feature(const_btree_new)`

---
 library/alloc/src/collections/btree/map.rs | 12 ++++++++++--
 library/alloc/src/collections/btree/set.rs | 12 ++++++++++--
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index 3018d1c9125..3687f84b1bd 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -2392,7 +2392,11 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_len", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn len(&self) -> usize {
         self.length
     }
@@ -2413,7 +2417,11 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_len", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 3caaf521240..5783d836e10 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -1174,7 +1174,11 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_len", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn len(&self) -> usize {
         self.map.len()
     }
@@ -1193,7 +1197,11 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_len", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }