Merge rust-bitcoin/rust-bitcoin#4365: Implement FromIterator for Witness

6bd7dc6980 feat(witness): implement FromIterator for Witness with unit test (aagbotemi)

Pull request description:

  This PR implements the FromIterator trait for the Witness struct, addressing issue #4351.

  Changes:
  - Added FromIterator<T: AsRef<[u8]>> implementation for Witness, allowing for convenient creation of Witness from iterators
  - Added unit test to verify the implementation works correctly

  This PR fixes #4351

ACKs for top commit:
  tcharding:
    ACK 6bd7dc6980
  apoelstra:
    ACK 6bd7dc69802ad809492fe44d8d87c4b287f93676; successfully ran local tests

Tree-SHA512: 660196c5027fb9270f9ae5c4e08eab6baa2afbdf19a2220b4777303f71f6802bd7ed5e1512af8ee14654b1249ec22606ea817951befbe85b13f9f285b3ebae12

primitives/src/witness.rs

@@ -403,6 +403,13 @@ impl<'a> IntoIterator for &'a Witness {
     fn into_iter(self) -> Self::IntoIter { self.iter() }
 }
 
+impl<T: AsRef<[u8]>> FromIterator<T> for Witness {
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+        let v: Vec<Vec<u8>> = iter.into_iter().map(|item| Vec::from(item.as_ref())).collect();
+        Self::from(v)
+    }
+}
+
 // Serde keep backward compatibility with old Vec<Vec<u8>> format
 #[cfg(feature = "serde")]
 impl serde::Serialize for Witness {
@@ -858,6 +865,39 @@ mod test {
         assert_eq!(json, r#"["007b4b","0206030708"]"#);
     }
 
+    #[test]
+    fn test_witness_from_iterator() {
+        let bytes1 = [1u8, 2, 3];
+        let bytes2 = [4u8, 5];
+        let bytes3 = [6u8, 7, 8, 9];
+        let data = [&bytes1[..], &bytes2[..], &bytes3[..]];
+
+        // Use FromIterator directly
+        let witness1 = Witness::from_iter(data);
+
+        // Create a witness manually for comparison
+        let mut witness2 = Witness::new();
+        for item in &data {
+            witness2.push(item);
+        }
+        assert_eq!(witness1, witness2);
+        assert_eq!(witness1.len(), witness2.len());
+        assert_eq!(witness1.to_vec(), witness2.to_vec());
+
+        // Test with collect
+        let bytes4 = [0u8, 123, 75];
+        let bytes5 = [2u8, 6, 3, 7, 8];
+        let data = [bytes4.to_vec(), bytes5.to_vec()];
+        let witness3: Witness = data.iter().collect();
+        assert_eq!(witness3.len(), 2);
+        assert_eq!(witness3.to_vec(), data);
+
+        // Test with empty iterator
+        let empty_data: Vec<Vec<u8>> = vec![];
+        let witness4: Witness = empty_data.iter().collect();
+        assert!(witness4.is_empty());
+    }
+    
     #[cfg(feature = "hex")]
     #[test]
     fn test_from_hex() {