From f0159f656d95d19b681e63b827538f6d0ca3367b Mon Sep 17 00:00:00 2001
From: Andy Freeland <andy@andyfreeland.net>
Date: Thu, 21 Oct 2021 14:06:55 -0700
Subject: [PATCH 1/2] Add `IndexMap::from(array)` and `IndexSet::from(array)`

This patch adds `IndexMap::from(array)` and `IndexSet::from(array)` to
match the API for `HashMap`, `HashSet`, etc. as of
https://github.com/rust-lang/rust/pull/84111.
---
 src/map.rs | 29 +++++++++++++++++++++++++++++
 src/set.rs | 27 +++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/src/map.rs b/src/map.rs
index 206e7eef..ad76a473 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -1345,6 +1345,25 @@ where
     }
 }
 
+#[cfg(has_std)]
+impl<K, V, const N: usize> From<[(K, V); N]> for IndexMap<K, V, RandomState>
+where
+    K: Hash + Eq,
+{
+    /// # Examples
+    ///
+    /// ```
+    /// use indexmap::IndexMap;
+    ///
+    /// let map1 = IndexMap::from([(1, 2), (3, 4)]);
+    /// let map2: IndexMap<_, _> = [(1, 2), (3, 4)].into();
+    /// assert_eq!(map1, map2);
+    /// ```
+    fn from(arr: [(K, V); N]) -> Self {
+        std::array::IntoIter::new(arr).collect()
+    }
+}
+
 impl<K, V, S> Extend<(K, V)> for IndexMap<K, V, S>
 where
     K: Hash + Eq,
@@ -1839,4 +1858,14 @@ mod tests {
         assert!(values.contains(&'b'));
         assert!(values.contains(&'c'));
     }
+
+    #[test]
+    fn from_array() {
+        let map = IndexMap::from([(1, 2), (3, 4)]);
+        let mut expected = IndexMap::new();
+        expected.insert(1, 2);
+        expected.insert(3, 4);
+
+        assert_eq!(map, expected)
+    }
 }
diff --git a/src/set.rs b/src/set.rs
index 5aabcf51..0322d25d 100644
--- a/src/set.rs
+++ b/src/set.rs
@@ -843,6 +843,25 @@ where
     }
 }
 
+#[cfg(has_std)]
+impl<T, const N: usize> From<[T; N]> for IndexSet<T, RandomState>
+where
+    T: Eq + Hash,
+{
+    /// # Examples
+    ///
+    /// ```
+    /// use indexmap::IndexSet;
+    ///
+    /// let set1 = IndexSet::from([1, 2, 3, 4]);
+    /// let set2: IndexSet<_> = [1, 2, 3, 4].into();
+    /// assert_eq!(set1, set2);
+    /// ```
+    fn from(arr: [T; N]) -> Self {
+        std::array::IntoIter::new(arr).collect()
+    }
+}
+
 impl<T, S> Extend<T> for IndexSet<T, S>
 where
     T: Hash + Eq,
@@ -1710,4 +1729,12 @@ mod tests {
         assert_eq!(&set_c - &set_d, set_a);
         assert_eq!(&set_d - &set_c, &set_d - &set_b);
     }
+
+    #[test]
+    fn from_array() {
+        let set1 = IndexSet::from([1, 2, 3, 4]);
+        let set2: IndexSet<_> = [1, 2, 3, 4].into();
+
+        assert_eq!(set1, set2);
+    }
 }

From 5d2ce528b3c431722581526b175a51528ae0efa0 Mon Sep 17 00:00:00 2001
From: Andy Freeland <andy@andyfreeland.net>
Date: Sun, 24 Oct 2021 13:15:04 -0700
Subject: [PATCH 2/2] Require rustc 1.51+ for `IndexMap::from(array)` and
 `IndexSet::from(array)`

https://github.com/rust-lang/rust/issues/74878 and
https://github.com/rust-lang/rust/issues/65798 were both stabilized in
1.51.
---
 build.rs   | 1 +
 src/map.rs | 3 ++-
 src/set.rs | 3 ++-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/build.rs b/build.rs
index 9f9fa054..7c5b6d5e 100644
--- a/build.rs
+++ b/build.rs
@@ -4,5 +4,6 @@ fn main() {
         Some(_) => autocfg::emit("has_std"),
         None => autocfg::new().emit_sysroot_crate("std"),
     }
+    autocfg::new().emit_rustc_version(1, 51);
     autocfg::rerun_path("build.rs");
 }
diff --git a/src/map.rs b/src/map.rs
index ad76a473..ca51b545 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -1345,7 +1345,7 @@ where
     }
 }
 
-#[cfg(has_std)]
+#[cfg(all(has_std, rustc_1_51))]
 impl<K, V, const N: usize> From<[(K, V); N]> for IndexMap<K, V, RandomState>
 where
     K: Hash + Eq,
@@ -1860,6 +1860,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(all(has_std, rustc_1_51))]
     fn from_array() {
         let map = IndexMap::from([(1, 2), (3, 4)]);
         let mut expected = IndexMap::new();
diff --git a/src/set.rs b/src/set.rs
index 0322d25d..f7d4b431 100644
--- a/src/set.rs
+++ b/src/set.rs
@@ -843,7 +843,7 @@ where
     }
 }
 
-#[cfg(has_std)]
+#[cfg(all(has_std, rustc_1_51))]
 impl<T, const N: usize> From<[T; N]> for IndexSet<T, RandomState>
 where
     T: Eq + Hash,
@@ -1731,6 +1731,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(all(has_std, rustc_1_51))]
     fn from_array() {
         let set1 = IndexSet::from([1, 2, 3, 4]);
         let set2: IndexSet<_> = [1, 2, 3, 4].into();