Don't hash constant values; only their types (#587)

* Don't hash constant values; only their types

* Fix a test

* cargo fmt

metadata/src/lib.rs

@@ -302,10 +302,8 @@ pub fn get_constant_hash(
         .find(|c| c.name == constant_name)
         .ok_or(NotFound::Item)?;
 
-    let mut bytes = get_type_hash(&metadata.types, constant.ty.id(), &mut HashSet::new());
-    bytes = xor(bytes, hash(constant.name.as_bytes()));
-    bytes = xor(bytes, hash(&constant.value));
-
+    // We only need to check that the type of the constant asked for matches.
+    let bytes = get_type_hash(&metadata.types, constant.ty.id(), &mut HashSet::new());
     Ok(bytes)
 }
 
@@ -363,7 +361,6 @@ pub fn get_pallet_hash(
     }
     for constant in pallet.constants.iter() {
         bytes = xor(bytes, hash(constant.name.as_bytes()));
-        bytes = xor(bytes, hash(&constant.value));
         bytes = xor(
             bytes,
             get_type_hash(registry, constant.ty.id(), &mut visited_ids),

testing/integration-tests/src/metadata/validation.rs

@@ -94,7 +94,7 @@ async fn full_metadata_check() {
 }
 
 #[tokio::test]
-async fn constants_check() {
+async fn constant_values_are_not_validated() {
     let cxt = test_context().await;
     let api = &cxt.api;
 
@@ -117,16 +117,14 @@ async fn constants_check() {
         .iter_mut()
         .find(|constant| constant.name == "ExistentialDeposit")
         .expect("ExistentialDeposit constant must be present");
+
+    // Modifying a constant value should not lead to an error:
     existential.value = vec![0u8; 32];
 
     let new_api = metadata_to_api(metadata, &cxt).await;
 
-    assert!(new_api.validate_metadata().is_err());
-    assert!(new_api
-        .constants()
-        .balances()
-        .existential_deposit()
-        .is_err());
+    assert!(new_api.validate_metadata().is_ok());
+    assert!(new_api.constants().balances().existential_deposit().is_ok());
 
     // Other constant validation should not be impacted.
     assert!(new_api.constants().balances().max_locks().is_ok());