Add new CompareFields trait and derive

eth2/utils/compare_fields/tests/tests.rs

@@ -0,0 +1,46 @@
+use compare_fields::{CompareFields, FieldComparison};
+use compare_fields_derive::CompareFields;
+
+#[derive(Clone, Debug, CompareFields)]
+pub struct Simple {
+    a: u64,
+    b: u16,
+    c: Vec<u8>,
+}
+
+#[test]
+fn compare() {
+    let foo = Simple {
+        a: 42,
+        b: 12,
+        c: vec![1, 2],
+    };
+
+    let mut bar = foo.clone();
+
+    let comparisons = foo.compare_fields(&bar);
+
+    assert!(!comparisons.iter().any(|c| c.equal == false));
+
+    assert_eq!(
+        comparisons[0],
+        FieldComparison {
+            equal: true,
+            field_name: "a".to_string(),
+            a: "42".to_string(),
+            b: "42".to_string(),
+        }
+    );
+
+    bar.a = 30;
+
+    assert_eq!(
+        foo.compare_fields(&bar)[0],
+        FieldComparison {
+            equal: false,
+            field_name: "a".to_string(),
+            a: "42".to_string(),
+            b: "30".to_string(),
+        }
+    );
+}