fix(tracer): Add error to flat tracer (#3306)

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---------

Signed-off-by: Danil <[email protected]>

core/lib/types/src/debug_flat_call.rs

@@ -16,6 +16,7 @@ pub struct DebugCallFlat {
     pub action: Action,
     pub result: Option<CallResult>,
     pub subtraces: usize,
+    pub error: Option<String>,
     pub trace_address: Vec<usize>,
     pub transaction_position: usize,
     pub transaction_hash: H256,

core/node/api_server/src/web3/namespaces/debug.rs

@@ -96,13 +96,16 @@ impl DebugNamespace {
             CallType::NearCall => unreachable!("We have to filter our near calls before"),
         };
 
-        let result = if call.error.is_none() {
-            Some(CallResult {
-                output: web3::Bytes::from(call.output),
-                gas_used: U256::from(call.gas_used),
-            })
+        let (result, error) = if let Some(error) = call.revert_reason {
+            (None, Some(error))
         } else {
-            None
+            (
+                Some(CallResult {
+                    output: web3::Bytes::from(call.output),
+                    gas_used: U256::from(call.gas_used),
+                }),
+                None,
+            )
         };
 
         calls.push(DebugCallFlat {
@@ -116,6 +119,7 @@ impl DebugNamespace {
             },
             result,
             subtraces,
+            error,
             trace_address: trace_address.clone(), // Clone the current trace address
             transaction_position: meta.index_in_block,
             transaction_hash: meta.tx_hash,