From d5ca01e408e1edbe438ab7586bdb0eda08350ead Mon Sep 17 00:00:00 2001
From: Michael Birch <michael.birch@aurora.dev>
Date: Thu, 9 Dec 2021 21:38:33 +0100
Subject: [PATCH] Feat(standalone): Add debug tracing of remaining gas values
 (#391)

---
 engine-standalone-tracing/src/sputnik.rs     | 12 ++++++++++--
 engine-standalone-tracing/src/types.rs       |  4 ++--
 engine-tests/src/tests/standalone/tracing.rs |  5 +++++
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/engine-standalone-tracing/src/sputnik.rs b/engine-standalone-tracing/src/sputnik.rs
index 799b59194..6e17e7437 100644
--- a/engine-standalone-tracing/src/sputnik.rs
+++ b/engine-standalone-tracing/src/sputnik.rs
@@ -48,14 +48,18 @@ impl evm_gasometer::tracing::EventListener for TransactionTraceBuilder {
     fn event(&mut self, event: evm_gasometer::tracing::Event) {
         use evm_gasometer::tracing::Event;
         match event {
-            Event::RecordCost { cost, snapshot: _ } => {
+            Event::RecordCost { cost, snapshot } => {
                 self.current.gas_cost = EthGas::new(cost);
+                if let Some(snapshot) = snapshot {
+                    self.current.gas =
+                        EthGas::new(snapshot.gas_limit - snapshot.used_gas - snapshot.memory_gas);
+                }
             }
             Event::RecordDynamicCost {
                 gas_cost,
                 memory_gas,
                 gas_refund: _,
-                snapshot: _,
+                snapshot,
             } => {
                 // In SputnikVM memory gas is cumulative (ie this event always shows the total) gas
                 // spent on memory up to this point. But geth traces simply show how much gas each step
@@ -68,6 +72,10 @@ impl evm_gasometer::tracing::EventListener for TransactionTraceBuilder {
                 };
                 self.current_memory_gas = memory_gas;
                 self.current.gas_cost = EthGas::new(gas_cost + memory_cost_diff);
+                if let Some(snapshot) = snapshot {
+                    self.current.gas =
+                        EthGas::new(snapshot.gas_limit - snapshot.used_gas - snapshot.memory_gas);
+                }
             }
             Event::RecordRefund {
                 refund: _,
diff --git a/engine-standalone-tracing/src/types.rs b/engine-standalone-tracing/src/types.rs
index 69b885593..adcea350c 100644
--- a/engine-standalone-tracing/src/types.rs
+++ b/engine-standalone-tracing/src/types.rs
@@ -151,9 +151,9 @@ pub struct TraceLog {
     pub depth: Depth,
     /// Any errors that may have occurred during execution.
     pub error: Option<String>,
-    /// Gas used to execute the transaction.
+    /// Remaining (unused) gas.
     pub gas: EthGas,
-    /// Gas cost for the transaction.
+    /// Gas cost for the opcode at this step.
     pub gas_cost: EthGas,
     /// The bounded memory.
     pub memory: LogMemory,
diff --git a/engine-tests/src/tests/standalone/tracing.rs b/engine-tests/src/tests/standalone/tracing.rs
index f6da0e8ee..f34475363 100644
--- a/engine-tests/src/tests/standalone/tracing.rs
+++ b/engine-tests/src/tests/standalone/tracing.rs
@@ -209,6 +209,11 @@ fn check_transaction_trace<P: AsRef<Path>>(trace: TransactionTrace, expected_tra
         );
         assert_eq!(log.depth.into_u32(), step.depth, "Depths should match");
         assert_eq!(log.opcode.as_u8(), step.op, "opcodes should match");
+        assert_eq!(
+            log.gas.into_u64(),
+            step.gas,
+            "remaining gas values should match"
+        );
         assert_eq!(
             log.gas_cost.into_u64(),
             step.gas_cost,