fix(forge): determine if broadcasted tx is fixed gas limit using opcodes

crates/cheatcodes/src/inspector.rs

@@ -499,6 +499,11 @@ pub struct Cheatcodes {
     pub wallets: Option<Wallets>,
     /// Signatures identifier for decoding events and functions
     pub signatures_identifier: Option<SignaturesIdentifier>,
+    /// Used to determine whether the broadcasted call has non-fixed gas limit.
+    /// Holds values for (seen opcode GAS, seen opcode CALL) pair.
+    /// If GAS opcode is followed by CALL opcode then both flags are marked true and call
+    /// has non-fixed gas limit, otherwise the call is considered to have fixed gas limit.
+    pub dynamic_gas_limit_sequence: Option<(bool, bool)>,
 }
 
 // This is not derived because calling this in `fn new` with `..Default::default()` creates a second
@@ -554,6 +559,7 @@ impl Cheatcodes {
             deprecated: Default::default(),
             wallets: Default::default(),
             signatures_identifier: SignaturesIdentifier::new(true).ok(),
+            dynamic_gas_limit_sequence: Default::default(),
         }
     }
 
@@ -852,8 +858,15 @@ impl Cheatcodes {
                         });
                     }
 
-                    let is_fixed_gas_limit = check_if_fixed_gas_limit(&ecx, call.gas_limit);
-
+                    let (gas_seen, call_seen) =
+                        self.dynamic_gas_limit_sequence.take().unwrap_or_default();
+                    // Transaction has fixed gas limit if no GAS opcode seen before CALL opcode.
+                    let mut is_fixed_gas_limit = !(gas_seen && call_seen);
+                    // Additional check as transfers in forge scripts seem to be estimated at 2300
+                    // by revm leading to "Intrinsic gas too low" failure when simulated on chain.
+                    if call.gas_limit < 21_000 {
+                        is_fixed_gas_limit = false;
+                    }
                     let input = TransactionInput::new(call.input.bytes(ecx));
                     // Ensure account is touched.
                     ecx.journaled_state.touch(broadcast.new_origin);
@@ -1077,6 +1090,10 @@ impl Inspector<EthEvmContext<&mut dyn DatabaseExt>> for Cheatcodes {
     fn step(&mut self, interpreter: &mut Interpreter, ecx: Ecx) {
         self.pc = interpreter.bytecode.pc();
 
+        if self.broadcast.is_some() {
+            self.record_gas_limit_opcode(interpreter);
+        }
+
         // `pauseGasMetering`: pause / resume interpreter gas.
         if self.gas_metering.paused {
             self.meter_gas(interpreter);
@@ -1117,6 +1134,10 @@ impl Inspector<EthEvmContext<&mut dyn DatabaseExt>> for Cheatcodes {
     }
 
     fn step_end(&mut self, interpreter: &mut Interpreter, ecx: Ecx) {
+        if self.broadcast.is_some() {
+            self.set_gas_limit_type(interpreter);
+        }
+
         if self.gas_metering.paused {
             self.meter_gas_end(interpreter);
         }
@@ -1614,7 +1635,7 @@ impl Inspector<EthEvmContext<&mut dyn DatabaseExt>> for Cheatcodes {
 
             if curr_depth == broadcast.depth {
                 input.set_caller(broadcast.new_origin);
-                let is_fixed_gas_limit = check_if_fixed_gas_limit(&ecx, input.gas_limit());
+
                 // Ensure account is touched.
                 ecx.journaled_state.touch(broadcast.new_origin);
 
@@ -1627,7 +1648,6 @@ impl Inspector<EthEvmContext<&mut dyn DatabaseExt>> for Cheatcodes {
                         value: Some(input.value()),
                         input: TransactionInput::new(input.init_code()),
                         nonce: Some(account.info.nonce),
-                        gas: if is_fixed_gas_limit { Some(input.gas_limit()) } else { None },
                         ..Default::default()
                     }
                     .into(),
@@ -2296,6 +2316,40 @@ impl Cheatcodes {
             (REVERT, 0, 1, false),
         );
     }
+
+    #[cold]
+    fn record_gas_limit_opcode(&mut self, interpreter: &mut Interpreter) {
+        match interpreter.bytecode.opcode() {
+            // If current opcode is CREATE2 then set non-fixed gas limit.
+            op::CREATE2 => self.dynamic_gas_limit_sequence = Some((true, true)),
+            op::GAS => {
+                if self.dynamic_gas_limit_sequence.is_none() {
+                    // If current opcode is GAS then mark as seen.
+                    self.dynamic_gas_limit_sequence = Some((true, false));
+                }
+            }
+            _ => {}
+        }
+    }
+
+    #[cold]
+    fn set_gas_limit_type(&mut self, interpreter: &mut Interpreter) {
+        // Early exit in case we already determined is non-fixed gas limit.
+        if matches!(self.dynamic_gas_limit_sequence, Some((true, true))) {
+            return;
+        }
+
+        // Record CALL opcode if GAS opcode was seen.
+        if matches!(self.dynamic_gas_limit_sequence, Some((true, false)))
+            && interpreter.bytecode.opcode() == op::CALL
+        {
+            self.dynamic_gas_limit_sequence = Some((true, true));
+            return;
+        }
+
+        // Reset dynamic gas limit sequence if GAS opcode was not followed by a CALL opcode.
+        self.dynamic_gas_limit_sequence = None;
+    }
 }
 
 /// Helper that expands memory, stores a revert string pertaining to a disallowed memory write,
@@ -2323,20 +2377,6 @@ fn disallowed_mem_write(
     ));
 }
 
-// Determines if the gas limit on a given call was manually set in the script and should therefore
-// not be overwritten by later estimations
-fn check_if_fixed_gas_limit(ecx: &Ecx, call_gas_limit: u64) -> bool {
-    // If the gas limit was not set in the source code it is set to the estimated gas left at the
-    // time of the call, which should be rather close to configured gas limit.
-    // TODO: Find a way to reliably make this determination.
-    // For example by generating it in the compilation or EVM simulation process
-    ecx.tx.gas_limit > ecx.block.gas_limit &&
-        call_gas_limit <= ecx.block.gas_limit
-        // Transfers in forge scripts seem to be estimated at 2300 by revm leading to "Intrinsic
-        // gas too low" failure when simulated on chain
-        && call_gas_limit > 2300
-}
-
 /// Returns true if the kind of account access is a call.
 fn access_is_call(kind: crate::Vm::AccountAccessKind) -> bool {
     matches!(