Return error when call was reverted

Cargo.toml

@@ -18,7 +18,7 @@ homepage = "https://github.com/Cardinal-Cryptography/drink"
 license = "Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/Cardinal-Cryptography/drink"
-version = "0.16.0"
+version = "0.17.0"
 
 [workspace.dependencies]
 anyhow = { version = "1.0.71" }
@@ -51,5 +51,5 @@ sp-runtime-interface = { version = "26.0.0" }
 
 # Local dependencies
 
-drink = { version = "=0.16.0", path = "drink" }
-drink-test-macro = { version = "=0.16.0", path = "drink/test-macro" }
+drink = { version = "=0.17.0", path = "drink" }
+drink-test-macro = { version = "=0.17.0", path = "drink/test-macro" }

drink/src/session.rs

@@ -463,6 +463,22 @@ where
         self.call_internal::<_, V>(None, message, args, endowment)
     }
 
+    /// Calls the last deployed contract. Expect it to be reverted and the message result to be of
+    /// type `Result<_, E>`.
+    pub fn call_and_expect_error<S: AsRef<str> + Debug, E: Debug + Decode>(
+        &mut self,
+        message: &str,
+        args: &[S],
+        endowment: Option<BalanceOf<T::Runtime>>,
+    ) -> E {
+        self.call_internal::<_, Result<(), E>>(None, message, args, endowment)
+            .expect_err("Call should fail")
+            .decode_revert::<Result<(), E>>()
+            .expect("Call should be reverted")
+            .expect("Call should return an error")
+            .expect_err("Call should return an error")
+    }
+
     /// Calls a contract with a given address. In case of a successful call, returns the encoded
     /// result.
     pub fn call_with_address<S: AsRef<str> + Debug, V: Decode>(
@@ -542,7 +558,9 @@ where
         });
 
         let ret = match &result.result {
-            Ok(exec_result) if exec_result.did_revert() => Err(SessionError::CallReverted),
+            Ok(exec_result) if exec_result.did_revert() => {
+                Err(SessionError::CallReverted(exec_result.data.clone()))
+            }
             Ok(exec_result) => {
                 self.record.push_call_return(exec_result.data.clone());
                 self.record.last_call_return_decoded::<V>()

drink/src/session/error.rs

@@ -1,8 +1,11 @@
 //! Module exposing errors and result types for the session API.
 
 use frame_support::sp_runtime::DispatchError;
+use parity_scale_codec::Decode;
 use thiserror::Error;
 
+use crate::errors::MessageResult;
+
 /// Session specific errors.
 #[derive(Error, Debug)]
 pub enum SessionError {
@@ -25,8 +28,8 @@ pub enum SessionError {
     #[error("Code upload failed: {0:?}")]
     UploadFailed(DispatchError),
     /// Call has been reverted by the contract.
-    #[error("Contract call has been reverted")]
-    CallReverted,
+    #[error("Contract call has been reverted. Encoded error: {0:?}")]
+    CallReverted(Vec<u8>),
     /// Contract call failed (aborted by the pallet).
     #[error("Contract call failed before execution: {0:?}")]
     CallFailed(DispatchError),
@@ -37,3 +40,15 @@ pub enum SessionError {
     #[error("Missing transcoder")]
     NoTranscoder,
 }
+
+impl SessionError {
+    /// Check if the error is a revert error and if so, decode the error message.
+    pub fn decode_revert<T: Decode>(&self) -> Option<MessageResult<T>> {
+        match self {
+            SessionError::CallReverted(error) => {
+                Some(MessageResult::decode(&mut &error[..]).expect("Failed to decode error"))
+            }
+            _ => None,
+        }
+    }
+}