Add unique_signers() to SDK (#10105)

automerge

sdk/src/signature.rs

@@ -3,6 +3,7 @@
 use crate::{pubkey::Pubkey, transaction::TransactionError};
 use generic_array::{typenum::U64, GenericArray};
 use hmac::Hmac;
+use itertools::Itertools;
 use rand::{rngs::OsRng, CryptoRng, RngCore};
 use std::{
     borrow::{Borrow, Cow},
@@ -155,6 +156,11 @@ impl std::fmt::Debug for dyn Signer {
     }
 }
 
+/// Remove duplicates signers while preserving order. O(n²)
+pub fn unique_signers(signers: Vec<&dyn Signer>) -> Vec<&dyn Signer> {
+    signers.into_iter().unique_by(|s| s.pubkey()).collect()
+}
+
 impl Signer for Keypair {
     /// Return the public key for the given keypair
     fn pubkey(&self) -> Pubkey {
@@ -553,4 +559,18 @@ mod tests {
         let presigner2 = Presigner::new(&pubkey, &sig);
         assert_eq!(presigner, presigner2);
     }
+
+    fn pubkeys(signers: &[&dyn Signer]) -> Vec<Pubkey> {
+        signers.into_iter().map(|x| x.pubkey()).collect()
+    }
+
+    #[test]
+    fn test_unique_signers() {
+        let alice = Keypair::new();
+        let bob = Keypair::new();
+        assert_eq!(
+            pubkeys(&unique_signers(vec![&alice, &bob, &alice])),
+            pubkeys(&[&alice, &bob])
+        );
+    }
 }