track only latest error so it doesn't leak

Author: orsinium

errors.go

@@ -6,4 +6,5 @@ var (
 	ErrRefNotFound = errors.New("HostRef with the given ID is not found in Refs")
 	ErrMemRead     = errors.New("Memory.Read is out of bounds")
 	ErrMemWrite    = errors.New("Memory.Write is out of bounds")
+	ErrRefCast     = errors.New("Reference returned by Refs.Get is not of the type expected by HostRef")
 )

store.go

@@ -39,8 +39,8 @@ type Store struct {
 	// Context can be retrieved by the [Context] type.
 	Context context.Context
 
-	// Errors is where all errors happening during [Lift] and [Lower] are pushed.
-	Errors []error
+	// Error holds the latest error that happened during [Lift] or [Lower].
+	Error error
 }
 
 // ValueTypes implements [Value] interface.

types_mem.go

@@ -28,7 +28,7 @@ func (Bytes) Lift(s Store) Bytes {
 	offset := uint32(s.Stack.Pop())
 	raw, ok := s.Memory.Read(offset, size)
 	if !ok {
-		s.Errors = append(s.Errors, ErrMemRead)
+		s.Error = ErrMemRead
 	}
 	return Bytes{Offset: offset, Raw: raw}
 }
@@ -37,7 +37,7 @@ func (Bytes) Lift(s Store) Bytes {
 func (v Bytes) Lower(s Store) {
 	ok := s.Memory.Write(v.Offset, v.Raw)
 	if !ok {
-		s.Errors = append(s.Errors, ErrMemWrite)
+		s.Error = ErrMemWrite
 	}
 	size := len(v.Raw)
 	s.Stack.Push(Raw(v.Offset))
@@ -72,7 +72,7 @@ func (String) Lift(s Store) String {
 	offset := uint32(s.Stack.Pop())
 	raw, ok := s.Memory.Read(offset, size)
 	if !ok {
-		s.Errors = append(s.Errors, ErrMemRead)
+		s.Error = ErrMemRead
 	}
 	return String{Offset: offset, Raw: string(raw)}
 }
@@ -81,7 +81,7 @@ func (String) Lift(s Store) String {
 func (v String) Lower(s Store) {
 	ok := s.Memory.Write(v.Offset, []byte(v.Raw))
 	if !ok {
-		s.Errors = append(s.Errors, ErrMemWrite)
+		s.Error = ErrMemWrite
 	}
 	size := len(v.Raw)
 	s.Stack.Push(Raw(v.Offset))

types_misc.go

@@ -295,10 +295,15 @@ func (HostRef[T]) Lift(s Store) HostRef[T] {
 	var def T
 	raw, found := s.Refs.Get(index, def)
 	if !found {
-		s.Errors = append(s.Errors, ErrRefNotFound)
+		s.Error = ErrRefNotFound
+	}
+	cast, ok := raw.(T)
+	if found && !ok {
+		s.Error = ErrRefCast
+		cast = def
 	}
 	return HostRef[T]{
-		Raw:   raw.(T),
+		Raw:   cast,
 		index: index,
 		refs:  s.Refs,
 	}