Fix up and document macros

packages/cw0/src/macros.rs

@@ -1,3 +1,11 @@
+/// Quick check for a guard. If the condition (first argument) is false,
+/// then return the second argument wrapped in Err(x).
+///
+///   ensure!(permissions.delegate, ContractError::DelegatePerm {});
+///  is the same as
+///   if !permissions.delegate {
+///     return Err(ContractError::DelegatePerm {});
+///   }
 #[macro_export]
 macro_rules! ensure {
     ($cond:expr, $e:expr) => {
@@ -7,11 +15,20 @@ macro_rules! ensure {
     };
 }
 
+/// Returns a generic error. In general, use ensure! with a specific ContractError variant,
+/// but some places we don't have one. This can make quick error messages in such cases.
+/// Uses .into() so that it can return StdError or any Error type with From<StdError> implemented.
+///
+///   ensure_generic!(id > 0, "Bad ID");
+/// is the same as
+///   if !(id > 0) {
+///     return Err(StdError::generic_err("Bad ID").into);
+///   }
 #[macro_export]
 macro_rules! ensure_generic {
     ($cond:expr, $e:expr) => {
         if !($cond) {
-            return cosmwasm_std::StdError::generic_err($e);
+            return Err(cosmwasm_std::StdError::generic_err($e).into());
         }
     };
 }