feat: Add nil-safety to runtime.Fetch:

- Return nil instead of panic on runtime.Fetch
- Ensure OpBegin works with type nil for reflect.Value.Len
- Improve perf on early return for nil from in builtin.lib.go.get
- Add expr.NilSafe() configuration

Author: Alysson Ribeiro

builtin/builtin.go

@@ -601,7 +601,9 @@ var Builtins = []*Function{
 					return
 				}
 			}()
-			return runtime.Fetch(args[0], 0), nil
+
+			value, _ := runtime.Fetch(args[0], 0)
+			return value, nil
 		},
 		Validate: func(args []reflect.Type) (reflect.Type, error) {
 			if len(args) != 1 {
@@ -624,7 +626,9 @@ var Builtins = []*Function{
 					return
 				}
 			}()
-			return runtime.Fetch(args[0], -1), nil
+
+			value, _ := runtime.Fetch(args[0], -1)
+			return value, nil
 		},
 		Validate: func(args []reflect.Type) (reflect.Type, error) {
 			if len(args) != 1 {

builtin/lib.go

@@ -548,13 +548,13 @@ func get(params ...any) (out any, err error) {
 		return nil, fmt.Errorf("invalid number of arguments (expected 2, got %d)", len(params))
 	}
 	from := params[0]
-	i := params[1]
-	v := reflect.ValueOf(from)
-
 	if from == nil {
 		return nil, nil
 	}
 
+	i := params[1]
+	v := reflect.ValueOf(from)
+
 	if v.Kind() == reflect.Invalid {
 		panic(fmt.Sprintf("cannot fetch %v from %T", i, from))
 	}

compiler/compiler.go

@@ -45,7 +45,11 @@ func Compile(tree *parser.Tree, config *conf.Config) (program *Program, err erro
 
 	c.compile(tree.Node)
 
+	nilSafe := false
+
 	if c.config != nil {
+		nilSafe = c.config.NilSafe
+
 		switch c.config.Expect {
 		case reflect.Int:
 			c.emit(OpCast, 0)
@@ -77,6 +81,7 @@ func Compile(tree *parser.Tree, config *conf.Config) (program *Program, err erro
 		c.functions,
 		c.debugInfo,
 		span,
+		nilSafe,
 	)
 	return
 }

conf/config.go

@@ -41,6 +41,9 @@ type Config struct {
 	// When enabled, the lexer treats `if`/`else` as identifiers and the parser
 	// will not parse `if` statements.
 	DisableIfOperator bool
+	// NilSafe enables nil-safe navigation for all expressions,
+	// allowing access to fields and methods on nil values without panicking.
+	NilSafe bool
 }
 
 // CreateNew creates new config with default values.
@@ -77,7 +80,14 @@ func (c *Config) ConstExpr(name string) {
 	if c.EnvObject == nil {
 		panic("no environment is specified for ConstExpr()")
 	}
-	fn := reflect.ValueOf(runtime.Fetch(c.EnvObject, name))
+
+	field, ok := runtime.Fetch(c.EnvObject, name)
+	if !ok {
+		panic(fmt.Errorf("cannot fetch %q in the environment", name))
+	}
+
+	fn := reflect.ValueOf(field)
+
 	if fn.Kind() != reflect.Func {
 		panic(fmt.Errorf("const expression %q must be a function", name))
 	}

expr.go

@@ -225,6 +225,12 @@ func MaxNodes(n uint) Option {
 	}
 }
 
+func NilSafe() Option {
+	return func(c *conf.Config) {
+		c.NilSafe = true
+	}
+}
+
 // Compile parses and compiles given input expression to bytecode program.
 func Compile(input string, ops ...Option) (*vm.Program, error) {
 	config := conf.CreateNew()

vm/program.go

@@ -28,6 +28,8 @@ type Program struct {
 	functions []Function
 	debugInfo map[string]string
 	span      *Span
+
+	nilSafe bool
 }
 
 // NewProgram returns a new Program. It's used by the compiler.
@@ -42,6 +44,7 @@ func NewProgram(
 	functions []Function,
 	debugInfo map[string]string,
 	span *Span,
+	nilSafe bool,
 ) *Program {
 	return &Program{
 		source:    source,
@@ -54,6 +57,7 @@ func NewProgram(
 		functions: functions,
 		debugInfo: debugInfo,
 		span:      span,
+		nilSafe:   nilSafe,
 	}
 }
 

vm/runtime/runtime.go

@@ -18,7 +18,11 @@ type fieldCacheKey struct {
 	f string
 }
 
-func Fetch(from, i any) any {
+func Fetch(from, i any) (any, bool) {
+	if from == nil {
+		return nil, false
+	}
+
 	v := reflect.ValueOf(from)
 	if v.Kind() == reflect.Invalid {
 		panic(fmt.Sprintf("cannot fetch %v from %T", i, from))
@@ -29,7 +33,7 @@ func Fetch(from, i any) any {
 		if methodName, ok := i.(string); ok {
 			method := v.MethodByName(methodName)
 			if method.IsValid() {
-				return method.Interface()
+				return method.Interface(), true
 			}
 		}
 	}
@@ -52,7 +56,7 @@ func Fetch(from, i any) any {
 		}
 		value := v.Index(index)
 		if value.IsValid() {
-			return value.Interface()
+			return value.Interface(), true
 		}
 
 	case reflect.Map:
@@ -63,10 +67,10 @@ func Fetch(from, i any) any {
 			value = v.MapIndex(reflect.ValueOf(i))
 		}
 		if value.IsValid() {
-			return value.Interface()
+			return value.Interface(), true
 		} else {
 			elem := reflect.TypeOf(from).Elem()
-			return reflect.Zero(elem).Interface()
+			return reflect.Zero(elem).Interface(), true
 		}
 
 	case reflect.Struct:
@@ -77,7 +81,7 @@ func Fetch(from, i any) any {
 			f: fieldName,
 		}
 		if cv, ok := fieldCache.Load(key); ok {
-			return v.FieldByIndex(cv.([]int)).Interface()
+			return v.FieldByIndex(cv.([]int)).Interface(), true
 		}
 		field, ok := t.FieldByNameFunc(func(name string) bool {
 			field, _ := t.FieldByName(name)
@@ -94,11 +98,12 @@ func Fetch(from, i any) any {
 			value := v.FieldByIndex(field.Index)
 			if value.IsValid() {
 				fieldCache.Store(key, field.Index)
-				return value.Interface()
+				return value.Interface(), true
 			}
 		}
 	}
-	panic(fmt.Sprintf("cannot fetch %v from %T", i, from))
+
+	return nil, false
 }
 
 type Field struct {

vm/vm.go

@@ -122,7 +122,12 @@ func (vm *VM) Run(program *Program, env any) (_ any, err error) {
 			vm.push(vm.Variables[arg])
 
 		case OpLoadConst:
-			vm.push(runtime.Fetch(env, program.Constants[arg]))
+			value, ok := runtime.Fetch(env, program.Constants[arg])
+			if !ok && !program.nilSafe {
+				panic(fmt.Sprintf("cannot fetch %v in the environment", program.Constants[arg]))
+			}
+
+			vm.push(value)
 
 		case OpLoadField:
 			vm.push(runtime.FetchField(env, program.Constants[arg].(*runtime.Field)))
@@ -139,7 +144,12 @@ func (vm *VM) Run(program *Program, env any) (_ any, err error) {
 		case OpFetch:
 			b := vm.pop()
 			a := vm.pop()
-			vm.push(runtime.Fetch(a, b))
+
+			value, ok := runtime.Fetch(a, b)
+			if !ok && !program.nilSafe {
+				panic(fmt.Sprintf("cannot fetch %v from %T", b, a))
+			}
+			vm.push(value)
 
 		case OpFetchField:
 			a := vm.pop()
@@ -609,6 +619,9 @@ func (vm *VM) Run(program *Program, env any) (_ any, err error) {
 			a := vm.pop()
 			s := vm.allocScope()
 			switch v := a.(type) {
+			case nil:
+				s.Len = 0
+				s.Anys = nil
 			case []int:
 				s.Ints = v
 				s.Len = len(v)

vm/vm_test.go

@@ -694,8 +694,9 @@ func TestVM_DirectCallOpcodes(t *testing.T) {
 				tt.bytecode,
 				tt.args,
 				tt.funcs,
-				nil, // debugInfo
-				nil, // span
+				nil,   // debugInfo
+				nil,   // span
+				false, // nilSafe
 			)
 			vm := &vm.VM{}
 			got, err := vm.Run(program, nil)
@@ -819,9 +820,10 @@ func TestVM_IndexAndCountOperations(t *testing.T) {
 				tt.consts,
 				tt.bytecode,
 				tt.args,
-				nil, // functions
-				nil, // debugInfo
-				nil, // span
+				nil,   // functions
+				nil,   // debugInfo
+				nil,   // span
+				false, // nilSafe
 			)
 			vm := &vm.VM{}
 			got, err := vm.Run(program, nil)
@@ -1288,9 +1290,10 @@ func TestVM_DirectBasicOpcodes(t *testing.T) {
 				tt.consts,
 				tt.bytecode,
 				tt.args,
-				nil, // functions
-				nil, // debugInfo
-				nil, // span
+				nil,   // functions
+				nil,   // debugInfo
+				nil,   // span
+				false, // nilSafe
 			)
 			vm := &vm.VM{}
 			got, err := vm.Run(program, tt.env)
@@ -1460,6 +1463,7 @@ func TestVM_OpJump_NegativeOffset(t *testing.T) {
 		nil,
 		nil,
 		nil,
+		false, // nilSafe
 	)
 
 	_, err := vm.Run(program, nil)