fix(multicall): impl Error for Failure + clear returns Empty bu…

…ilder. (#2043)

* fix: implement Error for `Failure`

* fix: clear should return Empty builder

* fix clear test

crates/contract/src/multicall.rs

@@ -261,12 +261,12 @@ mod tests {
         let provider = ProviderBuilder::new().on_anvil();
 
         let erc20 = ERC20::new(weth, &provider);
-        let mut multicall = provider
+        let multicall = provider
             .multicall()
             .add(erc20.totalSupply())
             .add(erc20.balanceOf(address!("d8dA6BF26964aF9D7eEd9e03E53415D37aA96045")));
         assert_eq!(multicall.len(), 2);
-        multicall.clear();
+        let multicall = multicall.clear();
         assert_eq!(multicall.len(), 0);
     }
 

crates/provider/src/provider/multicall/inner_types.rs

@@ -11,8 +11,9 @@ use thiserror::Error;
 /// Result type for multicall operations.
 pub type Result<T, E = MulticallError> = core::result::Result<T, E>;
 
-/// A struct to representing a failure in a multicall
-#[derive(Debug, Clone)]
+/// A struct representing a failure in a multicall
+#[derive(Debug, Clone, PartialEq, Eq, Error)]
+#[error("Call failed at index {idx} with return data: {return_data:?}")]
 pub struct Failure {
     /// The index-position of the call that failed
     pub idx: usize,

crates/provider/src/provider/multicall/mod.rs

@@ -660,9 +660,18 @@ where
         self.add_call(call)
     }
 
-    /// Clear the calls from the builder
-    pub fn clear(&mut self) {
-        self.calls.clear();
+    /// Returns an [`Empty`] builder
+    ///
+    /// Retains previously set provider, address, block and state_override settings.
+    pub fn clear(self) -> MulticallBuilder<Empty, P, N> {
+        MulticallBuilder {
+            calls: Vec::new(),
+            provider: self.provider,
+            block: self.block,
+            state_override: self.state_override,
+            address: self.address,
+            _pd: Default::default(),
+        }
     }
 
     /// Get the number of calls in the builder