From d924df6436db7c07cd613c0fb946410eadfd8067 Mon Sep 17 00:00:00 2001
From: Marco Neumann <marco@crepererum.net>
Date: Wed, 27 Jul 2022 11:04:48 +0200
Subject: [PATCH] Implement `Hash` for `Schema`

Closes #2182.
---
 arrow/src/datatypes/schema.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arrow/src/datatypes/schema.rs b/arrow/src/datatypes/schema.rs
index 5a7336624f5..1574b165462 100644
--- a/arrow/src/datatypes/schema.rs
+++ b/arrow/src/datatypes/schema.rs
@@ -18,6 +18,7 @@
 use std::collections::HashMap;
 use std::default::Default;
 use std::fmt;
+use std::hash::Hash;
 
 use serde_derive::{Deserialize, Serialize};
 use serde_json::{json, Value};
@@ -356,6 +357,22 @@ impl fmt::Display for Schema {
     }
 }
 
+// need to implement `Hash` manually because `HashMap` implement Eq but no `Hash`
+#[allow(clippy::derive_hash_xor_eq)]
+impl Hash for Schema {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.fields.hash(state);
+
+        // ensure deterministic key order
+        let mut keys: Vec<&String> = self.metadata.keys().collect();
+        keys.sort();
+        for k in keys {
+            k.hash(state);
+            self.metadata.get(k).expect("key valid").hash(state);
+        }
+    }
+}
+
 #[derive(Deserialize)]
 struct MetadataKeyValue {
     key: String,