Add preAction plugin callbacks which can return false to cancel the action

cmd/micro/plugin.go

@@ -20,12 +20,12 @@ var preInstalledPlugins = []string{
 // Call calls the lua function 'function'
 // If it does not exist nothing happens, if there is an error,
 // the error is returned
-func Call(function string, args []string) error {
+func Call(function string, args []string) (lua.LValue, error) {
 	var luaFunc lua.LValue
 	if strings.Contains(function, ".") {
 		plugin := L.GetGlobal(strings.Split(function, ".")[0])
 		if plugin.String() == "nil" {
-			return errors.New("function does not exist: " + function)
+			return nil, errors.New("function does not exist: " + function)
 		}
 		luaFunc = L.GetField(plugin, strings.Split(function, ".")[1])
 	} else {
@@ -33,7 +33,7 @@ func Call(function string, args []string) error {
 	}
 
 	if luaFunc.String() == "nil" {
-		return errors.New("function does not exist: " + function)
+		return nil, errors.New("function does not exist: " + function)
 	}
 	var luaArgs []lua.LValue
 	for _, v := range args {
@@ -41,10 +41,14 @@ func Call(function string, args []string) error {
 	}
 	err := L.CallByParam(lua.P{
 		Fn:      luaFunc,
-		NRet:    0,
+		NRet:    1,
 		Protect: true,
 	}, luaArgs...)
-	return err
+	ret := L.Get(-1) // returned value
+	if ret.String() != "nil" {
+		L.Pop(1) // remove received value
+	}
+	return ret, err
 }
 
 // LuaFunctionBinding is a function generator which takes the name of a lua function
@@ -53,7 +57,7 @@ func Call(function string, args []string) error {
 // to bind keys to lua functions
 func LuaFunctionBinding(function string) func(*View) bool {
 	return func(v *View) bool {
-		err := Call(function, nil)
+		_, err := Call(function, nil)
 		if err != nil {
 			TermMessage(err)
 		}
@@ -65,7 +69,7 @@ func LuaFunctionBinding(function string) func(*View) bool {
 // so that a command can be bound to a lua function
 func LuaFunctionCommand(function string) func([]string) {
 	return func(args []string) {
-		err := Call(function, args)
+		_, err := Call(function, args)
 		if err != nil {
 			TermMessage(err)
 		}
@@ -74,7 +78,7 @@ func LuaFunctionCommand(function string) func([]string) {
 
 func LuaFunctionJob(function string) func(string, ...string) {
 	return func(output string, args ...string) {
-		err := Call(function, append([]string{output}, args...))
+		_, err := Call(function, append([]string{output}, args...))
 		if err != nil {
 			TermMessage(err)
 		}

cmd/micro/view.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/mattn/go-runewidth"
+	"github.com/yuin/gopher-lua"
 	"github.com/zyedidia/tcell"
 )
 
@@ -366,7 +367,7 @@ func (v *View) HandleEvent(event tcell.Event) {
 			v.Cursor.Right()
 
 			for _, pl := range loadedPlugins {
-				err := Call(pl+".onRune", []string{string(e.Rune())})
+				_, err := Call(pl+".onRune", []string{string(e.Rune())})
 				if err != nil && !strings.HasPrefix(err.Error(), "function does not exist") {
 					TermMessage(err)
 				}
@@ -382,12 +383,26 @@ func (v *View) HandleEvent(event tcell.Event) {
 					if e.Modifiers() == key.modifiers {
 						relocate = false
 						for _, action := range actions {
-							relocate = action(v) || relocate
+							executeAction := true
+							funcName := strings.Split(runtime.FuncForPC(reflect.ValueOf(action).Pointer()).Name(), ".")
 							for _, pl := range loadedPlugins {
-								funcName := strings.Split(runtime.FuncForPC(reflect.ValueOf(action).Pointer()).Name(), ".")
-								err := Call(pl+".on"+funcName[len(funcName)-1], nil)
+								ret, err := Call(pl+".pre"+funcName[len(funcName)-1], nil)
 								if err != nil && !strings.HasPrefix(err.Error(), "function does not exist") {
 									TermMessage(err)
+									continue
+								}
+								if ret == lua.LFalse {
+									executeAction = false
+								}
+							}
+							if executeAction {
+								relocate = action(v) || relocate
+								for _, pl := range loadedPlugins {
+									_, err := Call(pl+".on"+funcName[len(funcName)-1], nil)
+									if err != nil && !strings.HasPrefix(err.Error(), "function does not exist") {
+										TermMessage(err)
+										continue
+									}
 								}
 							}
 						}