Change ExecError related functions to be associated-fns (privacy-scal…

…ing-explorations#1450)

### Description

This PR attempts to associate the function `get_step_reported_error` to
`ExecError`.

### Issue Link

Resolves privacy-scaling-explorations#1181 

### Type of change

- [x ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update

### Contents

### Rationale
We wanted to move the function `get_step_reported_error` to an `imp
ExecError`, I also moved the part related to `OogError` to its own
associated function `From<OpCodeId> for OogError`. I changed an if/else
block into a match expecting to handle more errors for CREATE/2.

Personally I would update the function `get_step_reported_error` to take
as input an `GethExecStep` and in that case directly implement it as a
`From<GethExecStep> for ExecError` but the return type should be changed
to `Option<ExecError>` since the step may not have an error (step.error
is optional).

### How Has This Been Tested?
No tests were added as no new functionalities were added.

bus-mapping/src/circuit_input_builder/input_state_ref.rs

@@ -6,10 +6,7 @@ use super::{
     TransactionContext,
 };
 use crate::{
-    error::{
-        get_step_reported_error, DepthError, ExecError, InsufficientBalanceError,
-        NonceUintOverflowError,
-    },
+    error::{DepthError, ExecError, InsufficientBalanceError, NonceUintOverflowError},
     exec_trace::OperationRef,
     operation::{
         AccountField, AccountOp, CallContextField, CallContextOp, MemoryOp, Op, OpEnum, Operation,
@@ -1155,8 +1152,8 @@ impl<'a> CircuitInputStateRef<'a> {
         step: &GethExecStep,
         next_step: Option<&GethExecStep>,
     ) -> Result<Option<ExecError>, Error> {
-        if let Some(error) = &step.error {
-            return Ok(Some(get_step_reported_error(&step.op, error)));
+        if let Ok(error) = ExecError::try_from(step) {
+            return Ok(Some(error));
         }
 
         if matches!(step.op, OpcodeId::INVALID(_)) {

bus-mapping/src/error.rs

@@ -98,6 +98,39 @@ pub enum OogError {
     SelfDestruct,
 }
 
+// Given OpCodeId, returns correponding OogError.
+impl From<&OpcodeId> for OogError {
+    fn from(op: &OpcodeId) -> Self {
+        match op {
+            OpcodeId::MLOAD | OpcodeId::MSTORE | OpcodeId::MSTORE8 => {
+                OogError::StaticMemoryExpansion
+            }
+            OpcodeId::CREATE | OpcodeId::RETURN | OpcodeId::REVERT => {
+                OogError::DynamicMemoryExpansion
+            }
+            OpcodeId::CALLDATACOPY
+            | OpcodeId::CODECOPY
+            | OpcodeId::EXTCODECOPY
+            | OpcodeId::RETURNDATACOPY => OogError::MemoryCopy,
+            OpcodeId::BALANCE | OpcodeId::EXTCODESIZE | OpcodeId::EXTCODEHASH => {
+                OogError::AccountAccess
+            }
+            OpcodeId::LOG0 | OpcodeId::LOG1 | OpcodeId::LOG2 | OpcodeId::LOG3 | OpcodeId::LOG4 => {
+                OogError::Log
+            }
+            OpcodeId::EXP => OogError::Exp,
+            OpcodeId::SHA3 => OogError::Sha3,
+            OpcodeId::CALL | OpcodeId::CALLCODE | OpcodeId::DELEGATECALL | OpcodeId::STATICCALL => {
+                OogError::Call
+            }
+            OpcodeId::SLOAD | OpcodeId::SSTORE => OogError::SloadSstore,
+            OpcodeId::CREATE2 => OogError::Create2,
+            OpcodeId::SELFDESTRUCT => OogError::SelfDestruct,
+            _ => OogError::Constant,
+        }
+    }
+}
+
 /// Insufficient balance errors by opcode/state.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum InsufficientBalanceError {
@@ -164,43 +197,26 @@ pub enum ExecError {
     NonceUintOverflow(NonceUintOverflowError),
 }
 
-// TODO: Move to impl block.
-pub(crate) fn get_step_reported_error(op: &OpcodeId, error: &str) -> ExecError {
-    if error == GETH_ERR_OUT_OF_GAS || error == GETH_ERR_GAS_UINT_OVERFLOW {
-        // NOTE: We report a GasUintOverflow error as an OutOfGas error
-        let oog_err = match op {
-            OpcodeId::MLOAD | OpcodeId::MSTORE | OpcodeId::MSTORE8 => {
-                OogError::StaticMemoryExpansion
-            }
-            OpcodeId::CREATE | OpcodeId::RETURN | OpcodeId::REVERT => {
-                OogError::DynamicMemoryExpansion
-            }
-            OpcodeId::CALLDATACOPY
-            | OpcodeId::CODECOPY
-            | OpcodeId::EXTCODECOPY
-            | OpcodeId::RETURNDATACOPY => OogError::MemoryCopy,
-            OpcodeId::BALANCE | OpcodeId::EXTCODESIZE | OpcodeId::EXTCODEHASH => {
-                OogError::AccountAccess
+// Returns a GethExecStep's error if present, else return the empty error.
+impl TryFrom<&GethExecStep> for ExecError {
+    type Error = ();
+
+    fn try_from(step: &GethExecStep) -> Result<Self, Self::Error> {
+        Ok(match step.error.as_ref().ok_or(())?.as_str() {
+            GETH_ERR_OUT_OF_GAS | GETH_ERR_GAS_UINT_OVERFLOW => {
+                // NOTE: We report a GasUintOverflow error as an OutOfGas error
+                let oog_err = OogError::from(&step.op);
+                ExecError::OutOfGas(oog_err)
             }
-            OpcodeId::LOG0 | OpcodeId::LOG1 | OpcodeId::LOG2 | OpcodeId::LOG3 | OpcodeId::LOG4 => {
-                OogError::Log
+            error => {
+                if error.starts_with(GETH_ERR_STACK_OVERFLOW) {
+                    ExecError::StackOverflow
+                } else if error.starts_with(GETH_ERR_STACK_UNDERFLOW) {
+                    ExecError::StackUnderflow
+                } else {
+                    panic!("Unknown GethExecStep.error: {}", error);
+                }
             }
-            OpcodeId::EXP => OogError::Exp,
-            OpcodeId::SHA3 => OogError::Sha3,
-            OpcodeId::CALL | OpcodeId::CALLCODE | OpcodeId::DELEGATECALL | OpcodeId::STATICCALL => {
-                OogError::Call
-            }
-            OpcodeId::SLOAD | OpcodeId::SSTORE => OogError::SloadSstore,
-            OpcodeId::CREATE2 => OogError::Create2,
-            OpcodeId::SELFDESTRUCT => OogError::SelfDestruct,
-            _ => OogError::Constant,
-        };
-        ExecError::OutOfGas(oog_err)
-    } else if error.starts_with(GETH_ERR_STACK_OVERFLOW) {
-        ExecError::StackOverflow
-    } else if error.starts_with(GETH_ERR_STACK_UNDERFLOW) {
-        ExecError::StackUnderflow
-    } else {
-        panic!("Unknown GethExecStep.error: {}", error);
+        })
     }
 }