Update example for migration

.github/workflows/doc-test.yml

@@ -26,6 +26,7 @@ jobs:
  cargo update -p cosmwasm-schema-derive
  cargo update -p cosmwasm-schema
  cargo update -p cosmwasm-std
+ cargo update -p cw2
  - uses: Swatinem/rust-cache@v2
  with:
  workspaces: |

docs-test-gen/Cargo.toml

@@ -12,5 +12,6 @@ pulldown-cmark = { version = "0.11.0", default-features = false }
 strum = { version = "0.26.2", features = ["derive"] }
 
 [dev-dependencies]
+cw2 = "*"
 cosmwasm-schema = "*"
 cosmwasm-std = { version = "*", features = ["stargate", "staking", "cosmwasm_2_0"] }

docs-test-gen/templates/core.tpl

@@ -21,18 +21,11 @@ struct MigrateMsg {}
 #[cw_serde]
 struct SudoMsg {}
 
-fn from_slice<T: Default>(_data: &[u8]) -> StdResult<T> {
- Ok(T::default())
-}
-
-fn to_vec<T>(_data: &T) -> StdResult<Vec<u8>> {
- Ok(Vec::new())
-}
-
 fn transform(_old_data: OldData) -> () {
  ()
 }
 
+#[cw_serde]
 #[derive(Default)]
 struct OldData {}
 

src/pages/core/entrypoints/migrate.mdx

@@ -48,32 +48,26 @@ the storage in there.
 ## Example
 
 ```rust filename="contract.rs" template="core"
-const STATE_VERSION: u64 = 1;
+const CONTRACT_NAME: &str = "my_contract";
+const STATE_VERSION: &str = "v2";
 
 #[entry_point]
 pub fn migrate(deps: DepsMut, _env: Env, _msg: MigrateMsg) -> StdResult<Response> {
  // Check if the state version is older than the current one
- let Some(current_state_version) = deps.storage.get(b"state") else {
- return Err(StdError::generic_err("State not found"));
- };
- let current_state_version: u64 = from_slice(&current_state_version)?;
-
- if current_state_version < STATE_VERSION {
- return Ok(Response::default());
- }
+ cw2::ensure_from_older_version(deps.storage, CONTRACT_NAME, STATE_VERSION)?;
 
  // Load the old data
  let Some(old_data) = deps.storage.get(b"persisted_data") else {
  return Err(StdError::generic_err("Data not found"));
  };
  // Deserialize it from the old format
- let old_data: OldData = from_slice(&old_data)?;
+ let old_data: OldData = cosmwasm_std::from_json(&old_data)?;
 
  // Transform it
  let new_data = transform(old_data);
 
  // Serialize the new data
- let new_data = to_vec(&new_data)?;
+ let new_data = cosmwasm_std::to_json_vec(&new_data)?;
  // Store the new data
  deps.storage.set(b"persisted_data", &new_data);