Merge pull request #2613 from OffchainLabs/gligneul/stylus-tracer-fixes

[NIT-2754] Two small comments on stylus tracer

execution/gethexec/stylus_tracer.go

@@ -5,6 +5,7 @@ package gethexec
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math/big"
 	"strings"
@@ -14,7 +15,8 @@ import (
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/vm"
 	"github.com/ethereum/go-ethereum/eth/tracers"
-	"github.com/offchainlabs/nitro/util/stack"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/offchainlabs/nitro/util/containers"
 )
 
 func init() {
@@ -24,8 +26,8 @@ func init() {
 // stylusTracer captures Stylus HostIOs and returns them in a structured format to be used in Cargo
 // Stylus Replay.
 type stylusTracer struct {
-	open      *stack.Stack[HostioTraceInfo]
-	stack     *stack.Stack[*stack.Stack[HostioTraceInfo]]
+	open      *containers.Stack[HostioTraceInfo]
+	stack     *containers.Stack[*containers.Stack[HostioTraceInfo]]
 	interrupt atomic.Bool
 	reason    error
 }
@@ -55,7 +57,7 @@ type HostioTraceInfo struct {
 	Address *common.Address `json:"address,omitempty"`
 
 	// For *call HostIOs, the steps performed by the called contract.
-	Steps *stack.Stack[HostioTraceInfo] `json:"steps,omitempty"`
+	Steps *containers.Stack[HostioTraceInfo] `json:"steps,omitempty"`
 }
 
 // nestsHostios contains the hostios with nested calls.
@@ -67,8 +69,8 @@ var nestsHostios = map[string]bool{
 
 func newStylusTracer(ctx *tracers.Context, _ json.RawMessage) (tracers.Tracer, error) {
 	return &stylusTracer{
-		open:  stack.NewStack[HostioTraceInfo](),
-		stack: stack.NewStack[*stack.Stack[HostioTraceInfo]](),
+		open:  containers.NewStack[HostioTraceInfo](),
+		stack: containers.NewStack[*containers.Stack[HostioTraceInfo]](),
 	}, nil
 }
 
@@ -126,7 +128,7 @@ func (t *stylusTracer) CaptureEnter(typ vm.OpCode, from common.Address, to commo
 		name = "evm_self_destruct"
 	}
 
-	inner := stack.NewStack[HostioTraceInfo]()
+	inner := containers.NewStack[HostioTraceInfo]()
 	info := HostioTraceInfo{
 		Name:    name,
 		Address: &to,
@@ -152,9 +154,22 @@ func (t *stylusTracer) GetResult() (json.RawMessage, error) {
 	if t.reason != nil {
 		return nil, t.reason
 	}
+
+	var internalErr error
 	if t.open == nil {
-		return nil, fmt.Errorf("trace is nil")
+		internalErr = errors.Join(internalErr, fmt.Errorf("tracer.open is nil"))
+	}
+	if t.stack == nil {
+		internalErr = errors.Join(internalErr, fmt.Errorf("tracer.stack is nil"))
+	}
+	if !t.stack.Empty() {
+		internalErr = errors.Join(internalErr, fmt.Errorf("tracer.stack should be empty, but has %d values", t.stack.Len()))
 	}
+	if internalErr != nil {
+		log.Error("stylusTracer: internal error when generating a trace", "error", internalErr)
+		return nil, fmt.Errorf("internal error: %w", internalErr)
+	}
+
 	msg, err := json.Marshal(t.open)
 	if err != nil {
 		return nil, err

system_tests/stylus_tracer_test.go

@@ -12,7 +12,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/offchainlabs/nitro/execution/gethexec"
 	"github.com/offchainlabs/nitro/solgen/go/mocksgen"
-	"github.com/offchainlabs/nitro/util/stack"
+	"github.com/offchainlabs/nitro/util/containers"
 	"github.com/offchainlabs/nitro/util/testhelpers"
 )
 
@@ -89,7 +89,7 @@ func TestStylusTracer(t *testing.T) {
 					Args:    append(stylusMulticall.Bytes(), common.Hex2Bytes("ffffffffffffffff000000000000000000000000000000000000000000000000000000000000000000")...),
 					Outs:    common.Hex2Bytes("0000000000"),
 					Address: &stylusMulticall,
-					Steps: (*stack.Stack[gethexec.HostioTraceInfo])(&[]gethexec.HostioTraceInfo{
+					Steps: (*containers.Stack[gethexec.HostioTraceInfo])(&[]gethexec.HostioTraceInfo{
 						{Name: "user_entrypoint", Args: intToBe32(1)},
 						{Name: "pay_for_memory_grow", Args: []byte{0x00, 0x01}},
 						{Name: "read_args", Outs: []byte{0x00}},
@@ -117,7 +117,7 @@ func TestStylusTracer(t *testing.T) {
 					Args:    append(evmMulticall.Bytes(), common.Hex2Bytes("ffffffffffffffff000000000000000000000000000000000000000000000000000000000000000000")...),
 					Outs:    common.Hex2Bytes("0000000000"),
 					Address: &evmMulticall,
-					Steps:   stack.NewStack[gethexec.HostioTraceInfo](),
+					Steps:   containers.NewStack[gethexec.HostioTraceInfo](),
 				},
 				{Name: "storage_flush_cache", Args: []byte{0x00}},
 				{Name: "write_result"},
@@ -133,7 +133,7 @@ func TestStylusTracer(t *testing.T) {
 				{
 					Name:    "evm_call_contract",
 					Address: &stylusMulticall,
-					Steps: (*stack.Stack[gethexec.HostioTraceInfo])(&[]gethexec.HostioTraceInfo{
+					Steps: (*containers.Stack[gethexec.HostioTraceInfo])(&[]gethexec.HostioTraceInfo{
 						{Name: "user_entrypoint", Args: intToBe32(1)},
 						{Name: "pay_for_memory_grow", Args: []byte{0x00, 0x01}},
 						{Name: "read_args", Outs: []byte{0x00}},

util/stack/stack.go → util/containers/stack.go

@@ -1,7 +1,7 @@
 // Copyright 2024, Offchain Labs, Inc.
 // For license information, see https://github.com/OffchainLabs/nitro/blob/master/LICENSE
 
-package stack
+package containers
 
 import (
 	"fmt"
@@ -28,7 +28,7 @@ func (s *Stack[T]) Pop() (T, error) {
 		var zeroVal T
 		return zeroVal, fmt.Errorf("trying to pop nil stack")
 	}
-	if len(*s) == 0 {
+	if s.Empty() {
 		var zeroVal T
 		return zeroVal, fmt.Errorf("trying to pop empty stack")
 	}
@@ -37,3 +37,14 @@ func (s *Stack[T]) Pop() (T, error) {
 	*s = (*s)[:i]
 	return val, nil
 }
+
+func (s *Stack[T]) Empty() bool {
+	return s == nil || len(*s) == 0
+}
+
+func (s *Stack[T]) Len() int {
+	if s == nil {
+		return 0
+	}
+	return len(*s)
+}