build: add shims for nightly feature map_first_last

lib/src/diff.rs

@@ -19,6 +19,8 @@ use std::ops::Range;
 
 use itertools::Itertools;
 
+use crate::nightly_shims::BTreeMapExt;
+
 pub fn find_line_ranges(text: &[u8]) -> Vec<Range<usize>> {
     let mut ranges = vec![];
     let mut start = 0;
@@ -175,7 +177,7 @@ pub(crate) fn unchanged_ranges(
 
     let max_occurrences = 100;
     let mut left_histogram = Histogram::calculate(left, left_ranges, max_occurrences);
-    if *left_histogram.count_to_words.first_entry().unwrap().key() > max_occurrences {
+    if *left_histogram.count_to_words.ext_first_key().unwrap() > max_occurrences {
         // If there are very many occurrences of all words, then we just give up.
         return vec![];
     }
@@ -185,7 +187,7 @@ pub(crate) fn unchanged_ranges(
     // the LCS.
     let mut uncommon_shared_words = vec![];
     while !left_histogram.count_to_words.is_empty() && uncommon_shared_words.is_empty() {
-        let left_words = left_histogram.count_to_words.pop_first().unwrap().1;
+        let left_words = left_histogram.count_to_words.ext_pop_first_value().unwrap();
         for left_word in left_words {
             if right_histogram.word_to_positions.contains_key(left_word) {
                 uncommon_shared_words.push(left_word);

lib/src/index.rs

@@ -34,6 +34,7 @@ use thiserror::Error;
 use crate::backend::{ChangeId, CommitId};
 use crate::commit::Commit;
 use crate::file_util::persist_content_addressed_temp_file;
+use crate::nightly_shims::BTreeSetExt;
 
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]
 pub struct IndexPosition(u32);
@@ -812,25 +813,25 @@ impl<'a> CompositeIndex<'a> {
 
         let mut result = BTreeSet::new();
         while !(items1.is_empty() || items2.is_empty()) {
-            let entry1 = items1.last().unwrap();
-            let entry2 = items2.last().unwrap();
+            let entry1 = items1.ext_last().unwrap();
+            let entry2 = items2.ext_last().unwrap();
             match entry1.cmp(entry2) {
                 Ordering::Greater => {
-                    let entry1 = items1.pop_last().unwrap();
+                    let entry1 = items1.ext_pop_last().unwrap();
                     for parent_entry in entry1.0.parents() {
                         items1.insert(IndexEntryByGeneration(parent_entry));
                     }
                 }
                 Ordering::Less => {
-                    let entry2 = items2.pop_last().unwrap();
+                    let entry2 = items2.ext_pop_last().unwrap();
                     for parent_entry in entry2.0.parents() {
                         items2.insert(IndexEntryByGeneration(parent_entry));
                     }
                 }
                 Ordering::Equal => {
                     result.insert(entry1.0.pos);
-                    items1.pop_last();
-                    items2.pop_last();
+                    items1.ext_pop_last();
+                    items2.ext_pop_last();
                 }
             }
         }

lib/src/lib.rs

@@ -13,7 +13,6 @@
 // limitations under the License.
 
 #![feature(assert_matches)]
-#![feature(map_first_last)]
 #![deny(unused_must_use)]
 
 #[macro_use]
@@ -39,6 +38,7 @@ pub mod index_store;
 pub mod local_backend;
 pub mod lock;
 pub mod matchers;
+pub mod nightly_shims;
 pub mod op_heads_store;
 pub mod op_store;
 pub mod operation;

lib/src/nightly_shims.rs

@@ -0,0 +1,61 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+pub trait BTreeMapExt<K, V> {
+    fn ext_first_key(&self) -> Option<&K>;
+    fn ext_last_key(&self) -> Option<&K>;
+    fn ext_pop_first_key(&mut self) -> Option<K>;
+    fn ext_pop_last_key(&mut self) -> Option<K>;
+    fn ext_pop_first_value(&mut self) -> Option<V>;
+    fn ext_pop_last_value(&mut self) -> Option<V>;
+}
+
+impl<K: Ord + Clone, V> BTreeMapExt<K, V> for BTreeMap<K, V> {
+    fn ext_first_key(&self) -> Option<&K> {
+        self.keys().next()
+    }
+
+    fn ext_last_key(&self) -> Option<&K> {
+        self.keys().next_back()
+    }
+
+    fn ext_pop_first_key(&mut self) -> Option<K> {
+        let key = self.ext_first_key()?;
+        let key = key.clone(); // ownership hack
+        Some(self.remove_entry(&key).unwrap().0)
+    }
+
+    fn ext_pop_last_key(&mut self) -> Option<K> {
+        let key = self.ext_last_key()?;
+        let key = key.clone(); // ownership hack
+        Some(self.remove_entry(&key).unwrap().0)
+    }
+
+    fn ext_pop_first_value(&mut self) -> Option<V> {
+        let key = self.ext_first_key()?;
+        let key = key.clone(); // ownership hack
+        Some(self.remove_entry(&key).unwrap().1)
+    }
+
+    fn ext_pop_last_value(&mut self) -> Option<V> {
+        let key = self.ext_last_key()?;
+        let key = key.clone(); // ownership hack
+        Some(self.remove_entry(&key).unwrap().1)
+    }
+}
+
+pub trait BTreeSetExt<K> {
+    fn ext_last(&self) -> Option<&K>;
+    fn ext_pop_last(&mut self) -> Option<K>;
+}
+
+impl<K: Ord + Clone> BTreeSetExt<K> for BTreeSet<K> {
+    fn ext_last(&self) -> Option<&K> {
+        self.iter().next_back()
+    }
+
+    fn ext_pop_last(&mut self) -> Option<K> {
+        let key = self.ext_last()?;
+        let key = key.clone(); // ownership hack
+        self.take(&key)
+    }
+}

lib/src/revset_graph_iterator.rs

@@ -16,6 +16,7 @@ use std::cmp::min;
 use std::collections::{BTreeMap, HashSet};
 
 use crate::index::{IndexEntry, IndexPosition};
+use crate::nightly_shims::BTreeMapExt;
 use crate::revset::RevsetIterator;
 
 #[derive(Debug, PartialEq, Eq, Clone, Hash)]
@@ -149,7 +150,7 @@ impl<'revset, 'repo> RevsetGraphIterator<'revset, 'repo> {
     }
 
     fn next_index_entry(&mut self) -> Option<IndexEntry<'repo>> {
-        if let Some((_, index_entry)) = self.look_ahead.pop_last() {
+        if let Some(index_entry) = self.look_ahead.ext_pop_last_value() {
             return Some(index_entry);
         }
         self.input_set_iter.next()