refactor: move SigChecker,Guard to dsl/ops/util package

Author: tyru

dsl/ops/func_do.go

@@ -3,6 +3,7 @@ package ops
 import (
 	"context"
 
+	"github.com/vim-volt/volt/dsl/ops/util"
 	"github.com/vim-volt/volt/dsl/types"
 )
 
@@ -30,7 +31,7 @@ func (*doOp) Bind(args ...types.Value) (*types.Expr, error) {
 	for i := 0; i < len(args); i++ {
 		sig = append(sig, types.AnyValue)
 	}
-	if err := signature(sig...).check(args); err != nil {
+	if err := util.Signature(sig...).Check(args); err != nil {
 		return nil, err
 	}
 	retType := args[len(args)-1].Type()
@@ -50,15 +51,15 @@ func (*doOp) InvertExpr(args []types.Value) (types.Value, error) {
 }
 
 func (*doOp) Execute(ctx context.Context, args []types.Value) (val types.Value, rollback func(), err error) {
-	g := funcGuard(DoOp.String())
-	defer func() { err = g.rollback(recover()) }()
-	rollback = g.rollbackForcefully
+	g := util.FuncGuard(DoOp.String())
+	defer func() { err = g.Rollback(recover()) }()
+	rollback = g.RollbackForcefully
 
 	for i := range args {
 		v, rbFunc, e := args[i].Eval(ctx)
-		g.add(rbFunc)
+		g.Add(rbFunc)
 		if e != nil {
-			err = g.rollback(e)
+			err = g.Rollback(e)
 			return
 		}
 		val = v

dsl/ops/guard.go

@@ -3,6 +3,7 @@ package ops
 import (
 	"context"
 
+	"github.com/vim-volt/volt/dsl/ops/util"
 	"github.com/vim-volt/volt/dsl/types"
 )
 
@@ -27,7 +28,7 @@ func (*evalOp) Bind(args ...types.Value) (*types.Expr, error) {
 }
 
 func (*evalOp) Execute(ctx context.Context, args []types.Value) (types.Value, func(), error) {
-	if err := signature(types.AnyValue).check(args); err != nil {
+	if err := util.Signature(types.AnyValue).Check(args); err != nil {
 		return nil, NoRollback, err
 	}
 	return args[0].Eval(context.Background())

dsl/ops/macro_eval.go

@@ -3,6 +3,7 @@ package ops
 import (
 	"context"
 
+	"github.com/vim-volt/volt/dsl/ops/util"
 	"github.com/vim-volt/volt/dsl/types"
 )
 
@@ -27,7 +28,7 @@ func (*invertOp) Bind(args ...types.Value) (*types.Expr, error) {
 }
 
 func (*invertOp) Execute(ctx context.Context, args []types.Value) (types.Value, func(), error) {
-	if err := signature(types.AnyValue).check(args); err != nil {
+	if err := util.Signature(types.AnyValue).Check(args); err != nil {
 		return nil, NoRollback, err
 	}
 	val, err := args[0].Invert()

dsl/ops/macro_invert.go

@@ -0,0 +1,63 @@
+package util
+
+import (
+	"fmt"
+	"github.com/pkg/errors"
+)
+
+// Guard invokes "rollback functions" if Rollback method received non-nil value
+// (e.g. recover(), non-nil error).
+type Guard interface {
+	// Rollback rolls back if v is non-nil.
+	//
+	//   defer func() { err = g.Rollback(recover()) }()
+	//
+	//   // or
+	//
+	//   if e != nil {
+	//     err = g.Rollback(e)
+	//     err = g.Rollback(e) // this won't call rollback functions twice!
+	//     return
+	//   }
+	Rollback(v interface{}) error
+
+	// RollbackForcefully calls rollback functions in reversed order
+	RollbackForcefully()
+
+	// Add adds given rollback functions
+	Add(f func())
+}
+
+// FuncGuard returns Guard instance for function
+func FuncGuard(name string) Guard {
+	return &guard{errMsg: fmt.Sprintf("function \"%s\" has an error", name)}
+}
+
+type guard struct {
+	errMsg  string
+	rbFuncs []func()
+}
+
+func (g *guard) Rollback(v interface{}) error {
+	var err error
+	if e, ok := v.(error); ok {
+		err = e
+	} else if v != nil {
+		err = fmt.Errorf("%s", v)
+	}
+	if err != nil {
+		g.RollbackForcefully()
+	}
+	return errors.Wrap(err, g.errMsg)
+}
+
+func (g *guard) RollbackForcefully() {
+	for i := len(g.rbFuncs) - 1; i >= 0; i-- {
+		g.rbFuncs[i]()
+	}
+	g.rbFuncs = nil // do not rollback twice
+}
+
+func (g *guard) Add(f func()) {
+	g.rbFuncs = append(g.rbFuncs, f)
+}

dsl/ops/util/guard.go

@@ -1,20 +1,26 @@
-package ops
+package util
 
 import (
 	"fmt"
 
 	"github.com/vim-volt/volt/dsl/types"
 )
 
-func signature(argTypes ...types.Type) *sigChecker {
+// SigChecker checks if the type of args met given types to Signature()
+type SigChecker interface {
+	Check(args []types.Value) error
+}
+
+// Signature returns SigChecker for given types
+func Signature(argTypes ...types.Type) SigChecker {
 	return &sigChecker{argTypes: argTypes}
 }
 
 type sigChecker struct {
 	argTypes []types.Type
 }
 
-func (sc *sigChecker) check(args []types.Value) error {
+func (sc *sigChecker) Check(args []types.Value) error {
 	if len(args) != len(sc.argTypes) {
 		return fmt.Errorf("expected %d arity but got %d", len(sc.argTypes), len(args))
 	}