feat: add precise diagnostics and optional client copy logging controls

copyx/copy.go

@@ -89,12 +89,14 @@ type visit struct {
 	target reflect.Type
 }
 type state struct {
-	options   *settings
-	seen      map[visit]reflect.Value
-	graph     *graph
-	nodes     int
-	allocated uint64
-	valueRoot *reference
+	options      *settings
+	seen         map[visit]reflect.Value
+	graph        *graph
+	nodes        int
+	allocated    uint64
+	valueRoot    *reference
+	checkedTypes map[pair]bool
+	checkedNodes int
 }
 
 func (s *state) reserve(count int, size uintptr, path string) error {
@@ -239,6 +241,11 @@ func (s *state) walk(src, base reflect.Value, t reflect.Type, path string, depth
 	case reflect.Struct:
 		return s.structure(src, base, t, path, depth)
 	case reflect.Slice:
+		if src.Len() == 0 {
+			if err := s.checkAbsent(src.Type(), t, path); err != nil {
+				return reflect.Value{}, err
+			}
+		}
 		if !s.options.deep && src.Type() == t {
 			return src, nil
 		}
@@ -264,6 +271,11 @@ func (s *state) walk(src, base reflect.Value, t reflect.Type, path string, depth
 		}
 		return out, nil
 	case reflect.Array:
+		if src.Len() == 0 {
+			if err := s.checkAbsent(src.Type(), t, path); err != nil {
+				return reflect.Value{}, err
+			}
+		}
 		if src.Len() != t.Len() {
 			return reflect.Value{}, at(path, ErrType)
 		}
@@ -280,6 +292,11 @@ func (s *state) walk(src, base reflect.Value, t reflect.Type, path string, depth
 		}
 		return out, nil
 	case reflect.Map:
+		if src.Len() == 0 {
+			if err := s.checkAbsent(src.Type(), t, path); err != nil {
+				return reflect.Value{}, err
+			}
+		}
 		if !s.options.deep && src.Type() == t {
 			return src, nil
 		}