MM-11734: better plugin error handling (#9405)

* MM-11734: encode unregistered error implementations as an ErrorString

* MM-11734: test error string handling

* more idiomatic error handling

app/plugin_hooks_test.go

@@ -13,6 +13,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/pkg/errors"
+
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/plugin"
 	"github.com/mattermost/mattermost-server/plugin/plugintest"
@@ -33,7 +35,7 @@ func compileGo(t *testing.T, sourceCode, outputPath string) {
 	require.NoError(t, cmd.Run())
 }
 
-func SetAppEnvironmentWithPlugins(t *testing.T, pluginCode []string, app *App, apiFunc func(*model.Manifest) plugin.API) {
+func SetAppEnvironmentWithPlugins(t *testing.T, pluginCode []string, app *App, apiFunc func(*model.Manifest) plugin.API) []error {
 	pluginDir, err := ioutil.TempDir("", "")
 	require.NoError(t, err)
 	webappPluginDir, err := ioutil.TempDir("", "")
@@ -45,14 +47,18 @@ func SetAppEnvironmentWithPlugins(t *testing.T, pluginCode []string, app *App, a
 	require.NoError(t, err)
 
 	app.Plugins = env
+	activationErrors := []error{}
 	for _, code := range pluginCode {
 		pluginId := model.NewId()
 		backend := filepath.Join(pluginDir, pluginId, "backend.exe")
 		compileGo(t, code, backend)
 
 		ioutil.WriteFile(filepath.Join(pluginDir, pluginId, "plugin.json"), []byte(`{"id": "`+pluginId+`", "backend": {"executable": "backend.exe"}}`), 0600)
-		env.Activate(pluginId)
+		_, _, activationErr := env.Activate(pluginId)
+		activationErrors = append(activationErrors, activationErr)
 	}
+
+	return activationErrors
 }
 
 func TestHookMessageWillBePosted(t *testing.T) {
@@ -791,3 +797,73 @@ func TestUserHasLoggedIn(t *testing.T) {
 		t.Errorf("Expected firstname overwrite, got default")
 	}
 }
+
+func TestErrorString(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	t.Run("errors.New", func(t *testing.T) {
+		activationErrors := SetAppEnvironmentWithPlugins(t,
+			[]string{
+				`
+			package main
+
+			import (
+				"github.com/pkg/errors"
+
+				"github.com/mattermost/mattermost-server/plugin"
+			)
+
+			type MyPlugin struct {
+				plugin.MattermostPlugin
+			}
+
+			func (p *MyPlugin) OnActivate() error {
+				return errors.New("simulate failure")
+			}
+
+			func main() {
+				plugin.ClientMain(&MyPlugin{})
+			}
+		`}, th.App, th.App.NewPluginAPI)
+
+		require.Len(t, activationErrors, 1)
+		require.NotNil(t, activationErrors[0])
+		require.Contains(t, activationErrors[0].Error(), "simulate failure")
+	})
+
+	t.Run("AppError", func(t *testing.T) {
+		activationErrors := SetAppEnvironmentWithPlugins(t,
+			[]string{
+				`
+			package main
+
+			import (
+				"github.com/mattermost/mattermost-server/plugin"
+				"github.com/mattermost/mattermost-server/model"
+			)
+
+			type MyPlugin struct {
+				plugin.MattermostPlugin
+			}
+
+			func (p *MyPlugin) OnActivate() error {
+				return model.NewAppError("where", "id", map[string]interface{}{"param": 1}, "details", 42)
+			}
+
+			func main() {
+				plugin.ClientMain(&MyPlugin{})
+			}
+		`}, th.App, th.App.NewPluginAPI)
+
+		require.Len(t, activationErrors, 1)
+		require.NotNil(t, activationErrors[0])
+
+		cause := errors.Cause(activationErrors[0])
+		require.IsType(t, &model.AppError{}, cause)
+
+		// params not expected, since not exported
+		expectedErr := model.NewAppError("where", "id", nil, "details", 42)
+		require.Equal(t, expectedErr, cause)
+	})
+}

plugin/client_rpc.go

@@ -62,12 +62,39 @@ type apiRPCServer struct {
 	impl API
 }
 
+// ErrorString is a fallback for sending unregistered implementations of the error interface across
+// rpc. For example, the errorString type from the github.com/pkg/errors package cannot be
+// registered since it is not exported, but this precludes common error handling paradigms.
+// ErrorString merely preserves the string description of the error, while satisfying the error
+// interface itself to allow other registered types (such as model.AppError) to be sent unmodified.
+type ErrorString struct {
+	Err string
+}
+
+func (e ErrorString) Error() string {
+	return e.Err
+}
+
+func encodableError(err error) error {
+	if err == nil {
+		return nil
+	}
+	if _, ok := err.(*model.AppError); ok {
+		return err
+	}
+
+	return &ErrorString{
+		Err: err.Error(),
+	}
+}
+
 // Registering some types used by MM for encoding/gob used by rpc
 func init() {
 	gob.Register([]*model.SlackAttachment{})
 	gob.Register([]interface{}{})
 	gob.Register(map[string]interface{}{})
 	gob.Register(&model.AppError{})
+	gob.Register(&ErrorString{})
 }
 
 // These enforce compile time checks to make sure types implement the interface
@@ -128,7 +155,7 @@ func (s *hooksRPCServer) Implemented(args struct{}, reply *[]string) error {
 		methods = append(methods, method.Name)
 	}
 	*reply = methods
-	return nil
+	return encodableError(nil)
 }
 
 type Z_OnActivateArgs struct {
@@ -182,7 +209,7 @@ func (s *hooksRPCServer) OnActivate(args *Z_OnActivateArgs, returns *Z_OnActivat
 	if hook, ok := s.impl.(interface {
 		OnActivate() error
 	}); ok {
-		returns.A = hook.OnActivate()
+		returns.A = encodableError(hook.OnActivate())
 	}
 	return nil
 }

plugin/client_rpc_generated.go

@@ -41,8 +41,9 @@ func (s *hooksRPCServer) OnDeactivate(args *Z_OnDeactivateArgs, returns *Z_OnDea
 		OnDeactivate() error
 	}); ok {
 		returns.A = hook.OnDeactivate()
+		returns.A = encodableError(returns.A)
 	} else {
-		return fmt.Errorf("Hook OnDeactivate called but not implemented.")
+		return encodableError(fmt.Errorf("Hook OnDeactivate called but not implemented."))
 	}
 	return nil
 }
@@ -74,8 +75,9 @@ func (s *hooksRPCServer) OnConfigurationChange(args *Z_OnConfigurationChangeArgs
 		OnConfigurationChange() error
 	}); ok {
 		returns.A = hook.OnConfigurationChange()
+		returns.A = encodableError(returns.A)
 	} else {
-		return fmt.Errorf("Hook OnConfigurationChange called but not implemented.")
+		return encodableError(fmt.Errorf("Hook OnConfigurationChange called but not implemented."))
 	}
 	return nil
 }
@@ -110,8 +112,9 @@ func (s *hooksRPCServer) ExecuteCommand(args *Z_ExecuteCommandArgs, returns *Z_E
 		ExecuteCommand(c *Context, args *model.CommandArgs) (*model.CommandResponse, *model.AppError)
 	}); ok {
 		returns.A, returns.B = hook.ExecuteCommand(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook ExecuteCommand called but not implemented.")
+		return encodableError(fmt.Errorf("Hook ExecuteCommand called but not implemented."))
 	}
 	return nil
 }
@@ -146,8 +149,9 @@ func (s *hooksRPCServer) MessageWillBePosted(args *Z_MessageWillBePostedArgs, re
 		MessageWillBePosted(c *Context, post *model.Post) (*model.Post, string)
 	}); ok {
 		returns.A, returns.B = hook.MessageWillBePosted(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook MessageWillBePosted called but not implemented.")
+		return encodableError(fmt.Errorf("Hook MessageWillBePosted called but not implemented."))
 	}
 	return nil
 }
@@ -183,8 +187,9 @@ func (s *hooksRPCServer) MessageWillBeUpdated(args *Z_MessageWillBeUpdatedArgs,
 		MessageWillBeUpdated(c *Context, newPost, oldPost *model.Post) (*model.Post, string)
 	}); ok {
 		returns.A, returns.B = hook.MessageWillBeUpdated(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook MessageWillBeUpdated called but not implemented.")
+		return encodableError(fmt.Errorf("Hook MessageWillBeUpdated called but not implemented."))
 	}
 	return nil
 }
@@ -217,8 +222,9 @@ func (s *hooksRPCServer) MessageHasBeenPosted(args *Z_MessageHasBeenPostedArgs,
 		MessageHasBeenPosted(c *Context, post *model.Post)
 	}); ok {
 		hook.MessageHasBeenPosted(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook MessageHasBeenPosted called but not implemented.")
+		return encodableError(fmt.Errorf("Hook MessageHasBeenPosted called but not implemented."))
 	}
 	return nil
 }
@@ -252,8 +258,9 @@ func (s *hooksRPCServer) MessageHasBeenUpdated(args *Z_MessageHasBeenUpdatedArgs
 		MessageHasBeenUpdated(c *Context, newPost, oldPost *model.Post)
 	}); ok {
 		hook.MessageHasBeenUpdated(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook MessageHasBeenUpdated called but not implemented.")
+		return encodableError(fmt.Errorf("Hook MessageHasBeenUpdated called but not implemented."))
 	}
 	return nil
 }
@@ -286,8 +293,9 @@ func (s *hooksRPCServer) ChannelHasBeenCreated(args *Z_ChannelHasBeenCreatedArgs
 		ChannelHasBeenCreated(c *Context, channel *model.Channel)
 	}); ok {
 		hook.ChannelHasBeenCreated(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook ChannelHasBeenCreated called but not implemented.")
+		return encodableError(fmt.Errorf("Hook ChannelHasBeenCreated called but not implemented."))
 	}
 	return nil
 }
@@ -321,8 +329,9 @@ func (s *hooksRPCServer) UserHasJoinedChannel(args *Z_UserHasJoinedChannelArgs,
 		UserHasJoinedChannel(c *Context, channelMember *model.ChannelMember, actor *model.User)
 	}); ok {
 		hook.UserHasJoinedChannel(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook UserHasJoinedChannel called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserHasJoinedChannel called but not implemented."))
 	}
 	return nil
 }
@@ -356,8 +365,9 @@ func (s *hooksRPCServer) UserHasLeftChannel(args *Z_UserHasLeftChannelArgs, retu
 		UserHasLeftChannel(c *Context, channelMember *model.ChannelMember, actor *model.User)
 	}); ok {
 		hook.UserHasLeftChannel(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook UserHasLeftChannel called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserHasLeftChannel called but not implemented."))
 	}
 	return nil
 }
@@ -391,8 +401,9 @@ func (s *hooksRPCServer) UserHasJoinedTeam(args *Z_UserHasJoinedTeamArgs, return
 		UserHasJoinedTeam(c *Context, teamMember *model.TeamMember, actor *model.User)
 	}); ok {
 		hook.UserHasJoinedTeam(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook UserHasJoinedTeam called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserHasJoinedTeam called but not implemented."))
 	}
 	return nil
 }
@@ -426,8 +437,9 @@ func (s *hooksRPCServer) UserHasLeftTeam(args *Z_UserHasLeftTeamArgs, returns *Z
 		UserHasLeftTeam(c *Context, teamMember *model.TeamMember, actor *model.User)
 	}); ok {
 		hook.UserHasLeftTeam(args.A, args.B, args.C)
+
 	} else {
-		return fmt.Errorf("Hook UserHasLeftTeam called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserHasLeftTeam called but not implemented."))
 	}
 	return nil
 }
@@ -461,8 +473,9 @@ func (s *hooksRPCServer) UserWillLogIn(args *Z_UserWillLogInArgs, returns *Z_Use
 		UserWillLogIn(c *Context, user *model.User) string
 	}); ok {
 		returns.A = hook.UserWillLogIn(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook UserWillLogIn called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserWillLogIn called but not implemented."))
 	}
 	return nil
 }
@@ -495,8 +508,9 @@ func (s *hooksRPCServer) UserHasLoggedIn(args *Z_UserHasLoggedInArgs, returns *Z
 		UserHasLoggedIn(c *Context, user *model.User)
 	}); ok {
 		hook.UserHasLoggedIn(args.A, args.B)
+
 	} else {
-		return fmt.Errorf("Hook UserHasLoggedIn called but not implemented.")
+		return encodableError(fmt.Errorf("Hook UserHasLoggedIn called but not implemented."))
 	}
 	return nil
 }
@@ -524,7 +538,7 @@ func (s *apiRPCServer) RegisterCommand(args *Z_RegisterCommandArgs, returns *Z_R
 	}); ok {
 		returns.A = hook.RegisterCommand(args.A)
 	} else {
-		return fmt.Errorf("API RegisterCommand called but not implemented.")
+		return encodableError(fmt.Errorf("API RegisterCommand called but not implemented."))
 	}
 	return nil
 }
@@ -553,7 +567,7 @@ func (s *apiRPCServer) UnregisterCommand(args *Z_UnregisterCommandArgs, returns
 	}); ok {
 		returns.A = hook.UnregisterCommand(args.A, args.B)
 	} else {
-		return fmt.Errorf("API UnregisterCommand called but not implemented.")
+		return encodableError(fmt.Errorf("API UnregisterCommand called but not implemented."))
 	}
 	return nil
 }
@@ -582,7 +596,7 @@ func (s *apiRPCServer) GetSession(args *Z_GetSessionArgs, returns *Z_GetSessionR
 	}); ok {
 		returns.A, returns.B = hook.GetSession(args.A)
 	} else {
-		return fmt.Errorf("API GetSession called but not implemented.")
+		return encodableError(fmt.Errorf("API GetSession called but not implemented."))
 	}
 	return nil
 }
@@ -609,7 +623,7 @@ func (s *apiRPCServer) GetConfig(args *Z_GetConfigArgs, returns *Z_GetConfigRetu
 	}); ok {
 		returns.A = hook.GetConfig()
 	} else {
-		return fmt.Errorf("API GetConfig called but not implemented.")
+		return encodableError(fmt.Errorf("API GetConfig called but not implemented."))
 	}
 	return nil
 }
@@ -637,7 +651,7 @@ func (s *apiRPCServer) SaveConfig(args *Z_SaveConfigArgs, returns *Z_SaveConfigR
 	}); ok {
 		returns.A = hook.SaveConfig(args.A)
 	} else {
-		return fmt.Errorf("API SaveConfig called but not implemented.")
+		return encodableError(fmt.Errorf("API SaveConfig called but not implemented."))
 	}
 	return nil
 }
@@ -666,7 +680,7 @@ func (s *apiRPCServer) CreateUser(args *Z_CreateUserArgs, returns *Z_CreateUserR
 	}); ok {
 		returns.A, returns.B = hook.CreateUser(args.A)
 	} else {
-		return fmt.Errorf("API CreateUser called but not implemented.")
+		return encodableError(fmt.Errorf("API CreateUser called but not implemented."))
 	}
 	return nil
 }
@@ -694,7 +708,7 @@ func (s *apiRPCServer) DeleteUser(args *Z_DeleteUserArgs, returns *Z_DeleteUserR
 	}); ok {
 		returns.A = hook.DeleteUser(args.A)
 	} else {
-		return fmt.Errorf("API DeleteUser called but not implemented.")
+		return encodableError(fmt.Errorf("API DeleteUser called but not implemented."))
 	}
 	return nil
 }
@@ -723,7 +737,7 @@ func (s *apiRPCServer) GetUser(args *Z_GetUserArgs, returns *Z_GetUserReturns) e
 	}); ok {
 		returns.A, returns.B = hook.GetUser(args.A)
 	} else {
-		return fmt.Errorf("API GetUser called but not implemented.")
+		return encodableError(fmt.Errorf("API GetUser called but not implemented."))
 	}
 	return nil
 }
@@ -752,7 +766,7 @@ func (s *apiRPCServer) GetUserByEmail(args *Z_GetUserByEmailArgs, returns *Z_Get
 	}); ok {
 		returns.A, returns.B = hook.GetUserByEmail(args.A)
 	} else {
-		return fmt.Errorf("API GetUserByEmail called but not implemented.")
+		return encodableError(fmt.Errorf("API GetUserByEmail called but not implemented."))
 	}
 	return nil
 }
@@ -781,7 +795,7 @@ func (s *apiRPCServer) GetUserByUsername(args *Z_GetUserByUsernameArgs, returns
 	}); ok {
 		returns.A, returns.B = hook.GetUserByUsername(args.A)
 	} else {
-		return fmt.Errorf("API GetUserByUsername called but not implemented.")
+		return encodableError(fmt.Errorf("API GetUserByUsername called but not implemented."))
 	}
 	return nil
 }
@@ -810,7 +824,7 @@ func (s *apiRPCServer) UpdateUser(args *Z_UpdateUserArgs, returns *Z_UpdateUserR
 	}); ok {
 		returns.A, returns.B = hook.UpdateUser(args.A)
 	} else {
-		return fmt.Errorf("API UpdateUser called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateUser called but not implemented."))
 	}
 	return nil
 }
@@ -839,7 +853,7 @@ func (s *apiRPCServer) GetUserStatus(args *Z_GetUserStatusArgs, returns *Z_GetUs
 	}); ok {
 		returns.A, returns.B = hook.GetUserStatus(args.A)
 	} else {
-		return fmt.Errorf("API GetUserStatus called but not implemented.")
+		return encodableError(fmt.Errorf("API GetUserStatus called but not implemented."))
 	}
 	return nil
 }
@@ -868,7 +882,7 @@ func (s *apiRPCServer) GetUserStatusesByIds(args *Z_GetUserStatusesByIdsArgs, re
 	}); ok {
 		returns.A, returns.B = hook.GetUserStatusesByIds(args.A)
 	} else {
-		return fmt.Errorf("API GetUserStatusesByIds called but not implemented.")
+		return encodableError(fmt.Errorf("API GetUserStatusesByIds called but not implemented."))
 	}
 	return nil
 }
@@ -898,7 +912,7 @@ func (s *apiRPCServer) UpdateUserStatus(args *Z_UpdateUserStatusArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.UpdateUserStatus(args.A, args.B)
 	} else {
-		return fmt.Errorf("API UpdateUserStatus called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateUserStatus called but not implemented."))
 	}
 	return nil
 }
@@ -928,7 +942,7 @@ func (s *apiRPCServer) GetLDAPUserAttributes(args *Z_GetLDAPUserAttributesArgs,
 	}); ok {
 		returns.A, returns.B = hook.GetLDAPUserAttributes(args.A, args.B)
 	} else {
-		return fmt.Errorf("API GetLDAPUserAttributes called but not implemented.")
+		return encodableError(fmt.Errorf("API GetLDAPUserAttributes called but not implemented."))
 	}
 	return nil
 }
@@ -957,7 +971,7 @@ func (s *apiRPCServer) CreateTeam(args *Z_CreateTeamArgs, returns *Z_CreateTeamR
 	}); ok {
 		returns.A, returns.B = hook.CreateTeam(args.A)
 	} else {
-		return fmt.Errorf("API CreateTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API CreateTeam called but not implemented."))
 	}
 	return nil
 }
@@ -985,7 +999,7 @@ func (s *apiRPCServer) DeleteTeam(args *Z_DeleteTeamArgs, returns *Z_DeleteTeamR
 	}); ok {
 		returns.A = hook.DeleteTeam(args.A)
 	} else {
-		return fmt.Errorf("API DeleteTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API DeleteTeam called but not implemented."))
 	}
 	return nil
 }
@@ -1013,7 +1027,7 @@ func (s *apiRPCServer) GetTeams(args *Z_GetTeamsArgs, returns *Z_GetTeamsReturns
 	}); ok {
 		returns.A, returns.B = hook.GetTeams()
 	} else {
-		return fmt.Errorf("API GetTeams called but not implemented.")
+		return encodableError(fmt.Errorf("API GetTeams called but not implemented."))
 	}
 	return nil
 }
@@ -1042,7 +1056,7 @@ func (s *apiRPCServer) GetTeam(args *Z_GetTeamArgs, returns *Z_GetTeamReturns) e
 	}); ok {
 		returns.A, returns.B = hook.GetTeam(args.A)
 	} else {
-		return fmt.Errorf("API GetTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API GetTeam called but not implemented."))
 	}
 	return nil
 }
@@ -1071,7 +1085,7 @@ func (s *apiRPCServer) GetTeamByName(args *Z_GetTeamByNameArgs, returns *Z_GetTe
 	}); ok {
 		returns.A, returns.B = hook.GetTeamByName(args.A)
 	} else {
-		return fmt.Errorf("API GetTeamByName called but not implemented.")
+		return encodableError(fmt.Errorf("API GetTeamByName called but not implemented."))
 	}
 	return nil
 }
@@ -1100,7 +1114,7 @@ func (s *apiRPCServer) UpdateTeam(args *Z_UpdateTeamArgs, returns *Z_UpdateTeamR
 	}); ok {
 		returns.A, returns.B = hook.UpdateTeam(args.A)
 	} else {
-		return fmt.Errorf("API UpdateTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateTeam called but not implemented."))
 	}
 	return nil
 }
@@ -1130,7 +1144,7 @@ func (s *apiRPCServer) CreateTeamMember(args *Z_CreateTeamMemberArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.CreateTeamMember(args.A, args.B)
 	} else {
-		return fmt.Errorf("API CreateTeamMember called but not implemented.")
+		return encodableError(fmt.Errorf("API CreateTeamMember called but not implemented."))
 	}
 	return nil
 }
@@ -1161,7 +1175,7 @@ func (s *apiRPCServer) CreateTeamMembers(args *Z_CreateTeamMembersArgs, returns
 	}); ok {
 		returns.A, returns.B = hook.CreateTeamMembers(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API CreateTeamMembers called but not implemented.")
+		return encodableError(fmt.Errorf("API CreateTeamMembers called but not implemented."))
 	}
 	return nil
 }
@@ -1191,7 +1205,7 @@ func (s *apiRPCServer) DeleteTeamMember(args *Z_DeleteTeamMemberArgs, returns *Z
 	}); ok {
 		returns.A = hook.DeleteTeamMember(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API DeleteTeamMember called but not implemented.")
+		return encodableError(fmt.Errorf("API DeleteTeamMember called but not implemented."))
 	}
 	return nil
 }
@@ -1222,7 +1236,7 @@ func (s *apiRPCServer) GetTeamMembers(args *Z_GetTeamMembersArgs, returns *Z_Get
 	}); ok {
 		returns.A, returns.B = hook.GetTeamMembers(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API GetTeamMembers called but not implemented.")
+		return encodableError(fmt.Errorf("API GetTeamMembers called but not implemented."))
 	}
 	return nil
 }
@@ -1252,7 +1266,7 @@ func (s *apiRPCServer) GetTeamMember(args *Z_GetTeamMemberArgs, returns *Z_GetTe
 	}); ok {
 		returns.A, returns.B = hook.GetTeamMember(args.A, args.B)
 	} else {
-		return fmt.Errorf("API GetTeamMember called but not implemented.")
+		return encodableError(fmt.Errorf("API GetTeamMember called but not implemented."))
 	}
 	return nil
 }
@@ -1283,7 +1297,7 @@ func (s *apiRPCServer) UpdateTeamMemberRoles(args *Z_UpdateTeamMemberRolesArgs,
 	}); ok {
 		returns.A, returns.B = hook.UpdateTeamMemberRoles(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API UpdateTeamMemberRoles called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateTeamMemberRoles called but not implemented."))
 	}
 	return nil
 }
@@ -1312,7 +1326,7 @@ func (s *apiRPCServer) CreateChannel(args *Z_CreateChannelArgs, returns *Z_Creat
 	}); ok {
 		returns.A, returns.B = hook.CreateChannel(args.A)
 	} else {
-		return fmt.Errorf("API CreateChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API CreateChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1340,7 +1354,7 @@ func (s *apiRPCServer) DeleteChannel(args *Z_DeleteChannelArgs, returns *Z_Delet
 	}); ok {
 		returns.A = hook.DeleteChannel(args.A)
 	} else {
-		return fmt.Errorf("API DeleteChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API DeleteChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1371,7 +1385,7 @@ func (s *apiRPCServer) GetPublicChannelsForTeam(args *Z_GetPublicChannelsForTeam
 	}); ok {
 		returns.A, returns.B = hook.GetPublicChannelsForTeam(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API GetPublicChannelsForTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API GetPublicChannelsForTeam called but not implemented."))
 	}
 	return nil
 }
@@ -1400,7 +1414,7 @@ func (s *apiRPCServer) GetChannel(args *Z_GetChannelArgs, returns *Z_GetChannelR
 	}); ok {
 		returns.A, returns.B = hook.GetChannel(args.A)
 	} else {
-		return fmt.Errorf("API GetChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API GetChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1431,7 +1445,7 @@ func (s *apiRPCServer) GetChannelByName(args *Z_GetChannelByNameArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.GetChannelByName(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API GetChannelByName called but not implemented.")
+		return encodableError(fmt.Errorf("API GetChannelByName called but not implemented."))
 	}
 	return nil
 }
@@ -1462,7 +1476,7 @@ func (s *apiRPCServer) GetChannelByNameForTeamName(args *Z_GetChannelByNameForTe
 	}); ok {
 		returns.A, returns.B = hook.GetChannelByNameForTeamName(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API GetChannelByNameForTeamName called but not implemented.")
+		return encodableError(fmt.Errorf("API GetChannelByNameForTeamName called but not implemented."))
 	}
 	return nil
 }
@@ -1492,7 +1506,7 @@ func (s *apiRPCServer) GetDirectChannel(args *Z_GetDirectChannelArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.GetDirectChannel(args.A, args.B)
 	} else {
-		return fmt.Errorf("API GetDirectChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API GetDirectChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1521,7 +1535,7 @@ func (s *apiRPCServer) GetGroupChannel(args *Z_GetGroupChannelArgs, returns *Z_G
 	}); ok {
 		returns.A, returns.B = hook.GetGroupChannel(args.A)
 	} else {
-		return fmt.Errorf("API GetGroupChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API GetGroupChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1550,7 +1564,7 @@ func (s *apiRPCServer) UpdateChannel(args *Z_UpdateChannelArgs, returns *Z_Updat
 	}); ok {
 		returns.A, returns.B = hook.UpdateChannel(args.A)
 	} else {
-		return fmt.Errorf("API UpdateChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateChannel called but not implemented."))
 	}
 	return nil
 }
@@ -1580,7 +1594,7 @@ func (s *apiRPCServer) AddChannelMember(args *Z_AddChannelMemberArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.AddChannelMember(args.A, args.B)
 	} else {
-		return fmt.Errorf("API AddChannelMember called but not implemented.")
+		return encodableError(fmt.Errorf("API AddChannelMember called but not implemented."))
 	}
 	return nil
 }
@@ -1610,7 +1624,7 @@ func (s *apiRPCServer) GetChannelMember(args *Z_GetChannelMemberArgs, returns *Z
 	}); ok {
 		returns.A, returns.B = hook.GetChannelMember(args.A, args.B)
 	} else {
-		return fmt.Errorf("API GetChannelMember called but not implemented.")
+		return encodableError(fmt.Errorf("API GetChannelMember called but not implemented."))
 	}
 	return nil
 }
@@ -1641,7 +1655,7 @@ func (s *apiRPCServer) UpdateChannelMemberRoles(args *Z_UpdateChannelMemberRoles
 	}); ok {
 		returns.A, returns.B = hook.UpdateChannelMemberRoles(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API UpdateChannelMemberRoles called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateChannelMemberRoles called but not implemented."))
 	}
 	return nil
 }
@@ -1672,7 +1686,7 @@ func (s *apiRPCServer) UpdateChannelMemberNotifications(args *Z_UpdateChannelMem
 	}); ok {
 		returns.A, returns.B = hook.UpdateChannelMemberNotifications(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API UpdateChannelMemberNotifications called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdateChannelMemberNotifications called but not implemented."))
 	}
 	return nil
 }
@@ -1701,7 +1715,7 @@ func (s *apiRPCServer) DeleteChannelMember(args *Z_DeleteChannelMemberArgs, retu
 	}); ok {
 		returns.A = hook.DeleteChannelMember(args.A, args.B)
 	} else {
-		return fmt.Errorf("API DeleteChannelMember called but not implemented.")
+		return encodableError(fmt.Errorf("API DeleteChannelMember called but not implemented."))
 	}
 	return nil
 }
@@ -1730,7 +1744,7 @@ func (s *apiRPCServer) CreatePost(args *Z_CreatePostArgs, returns *Z_CreatePostR
 	}); ok {
 		returns.A, returns.B = hook.CreatePost(args.A)
 	} else {
-		return fmt.Errorf("API CreatePost called but not implemented.")
+		return encodableError(fmt.Errorf("API CreatePost called but not implemented."))
 	}
 	return nil
 }
@@ -1759,7 +1773,7 @@ func (s *apiRPCServer) AddReaction(args *Z_AddReactionArgs, returns *Z_AddReacti
 	}); ok {
 		returns.A, returns.B = hook.AddReaction(args.A)
 	} else {
-		return fmt.Errorf("API AddReaction called but not implemented.")
+		return encodableError(fmt.Errorf("API AddReaction called but not implemented."))
 	}
 	return nil
 }
@@ -1787,7 +1801,7 @@ func (s *apiRPCServer) RemoveReaction(args *Z_RemoveReactionArgs, returns *Z_Rem
 	}); ok {
 		returns.A = hook.RemoveReaction(args.A)
 	} else {
-		return fmt.Errorf("API RemoveReaction called but not implemented.")
+		return encodableError(fmt.Errorf("API RemoveReaction called but not implemented."))
 	}
 	return nil
 }
@@ -1816,7 +1830,7 @@ func (s *apiRPCServer) GetReactions(args *Z_GetReactionsArgs, returns *Z_GetReac
 	}); ok {
 		returns.A, returns.B = hook.GetReactions(args.A)
 	} else {
-		return fmt.Errorf("API GetReactions called but not implemented.")
+		return encodableError(fmt.Errorf("API GetReactions called but not implemented."))
 	}
 	return nil
 }
@@ -1845,7 +1859,7 @@ func (s *apiRPCServer) SendEphemeralPost(args *Z_SendEphemeralPostArgs, returns
 	}); ok {
 		returns.A = hook.SendEphemeralPost(args.A, args.B)
 	} else {
-		return fmt.Errorf("API SendEphemeralPost called but not implemented.")
+		return encodableError(fmt.Errorf("API SendEphemeralPost called but not implemented."))
 	}
 	return nil
 }
@@ -1873,7 +1887,7 @@ func (s *apiRPCServer) DeletePost(args *Z_DeletePostArgs, returns *Z_DeletePostR
 	}); ok {
 		returns.A = hook.DeletePost(args.A)
 	} else {
-		return fmt.Errorf("API DeletePost called but not implemented.")
+		return encodableError(fmt.Errorf("API DeletePost called but not implemented."))
 	}
 	return nil
 }
@@ -1902,7 +1916,7 @@ func (s *apiRPCServer) GetPost(args *Z_GetPostArgs, returns *Z_GetPostReturns) e
 	}); ok {
 		returns.A, returns.B = hook.GetPost(args.A)
 	} else {
-		return fmt.Errorf("API GetPost called but not implemented.")
+		return encodableError(fmt.Errorf("API GetPost called but not implemented."))
 	}
 	return nil
 }
@@ -1931,7 +1945,7 @@ func (s *apiRPCServer) UpdatePost(args *Z_UpdatePostArgs, returns *Z_UpdatePostR
 	}); ok {
 		returns.A, returns.B = hook.UpdatePost(args.A)
 	} else {
-		return fmt.Errorf("API UpdatePost called but not implemented.")
+		return encodableError(fmt.Errorf("API UpdatePost called but not implemented."))
 	}
 	return nil
 }
@@ -1961,7 +1975,7 @@ func (s *apiRPCServer) CopyFileInfos(args *Z_CopyFileInfosArgs, returns *Z_CopyF
 	}); ok {
 		returns.A, returns.B = hook.CopyFileInfos(args.A, args.B)
 	} else {
-		return fmt.Errorf("API CopyFileInfos called but not implemented.")
+		return encodableError(fmt.Errorf("API CopyFileInfos called but not implemented."))
 	}
 	return nil
 }
@@ -1990,7 +2004,7 @@ func (s *apiRPCServer) GetFileInfo(args *Z_GetFileInfoArgs, returns *Z_GetFileIn
 	}); ok {
 		returns.A, returns.B = hook.GetFileInfo(args.A)
 	} else {
-		return fmt.Errorf("API GetFileInfo called but not implemented.")
+		return encodableError(fmt.Errorf("API GetFileInfo called but not implemented."))
 	}
 	return nil
 }
@@ -2019,7 +2033,7 @@ func (s *apiRPCServer) ReadFile(args *Z_ReadFileArgs, returns *Z_ReadFileReturns
 	}); ok {
 		returns.A, returns.B = hook.ReadFile(args.A)
 	} else {
-		return fmt.Errorf("API ReadFile called but not implemented.")
+		return encodableError(fmt.Errorf("API ReadFile called but not implemented."))
 	}
 	return nil
 }
@@ -2048,7 +2062,7 @@ func (s *apiRPCServer) KVSet(args *Z_KVSetArgs, returns *Z_KVSetReturns) error {
 	}); ok {
 		returns.A = hook.KVSet(args.A, args.B)
 	} else {
-		return fmt.Errorf("API KVSet called but not implemented.")
+		return encodableError(fmt.Errorf("API KVSet called but not implemented."))
 	}
 	return nil
 }
@@ -2077,7 +2091,7 @@ func (s *apiRPCServer) KVGet(args *Z_KVGetArgs, returns *Z_KVGetReturns) error {
 	}); ok {
 		returns.A, returns.B = hook.KVGet(args.A)
 	} else {
-		return fmt.Errorf("API KVGet called but not implemented.")
+		return encodableError(fmt.Errorf("API KVGet called but not implemented."))
 	}
 	return nil
 }
@@ -2105,7 +2119,7 @@ func (s *apiRPCServer) KVDelete(args *Z_KVDeleteArgs, returns *Z_KVDeleteReturns
 	}); ok {
 		returns.A = hook.KVDelete(args.A)
 	} else {
-		return fmt.Errorf("API KVDelete called but not implemented.")
+		return encodableError(fmt.Errorf("API KVDelete called but not implemented."))
 	}
 	return nil
 }
@@ -2134,7 +2148,7 @@ func (s *apiRPCServer) PublishWebSocketEvent(args *Z_PublishWebSocketEventArgs,
 	}); ok {
 		hook.PublishWebSocketEvent(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API PublishWebSocketEvent called but not implemented.")
+		return encodableError(fmt.Errorf("API PublishWebSocketEvent called but not implemented."))
 	}
 	return nil
 }
@@ -2163,7 +2177,7 @@ func (s *apiRPCServer) HasPermissionTo(args *Z_HasPermissionToArgs, returns *Z_H
 	}); ok {
 		returns.A = hook.HasPermissionTo(args.A, args.B)
 	} else {
-		return fmt.Errorf("API HasPermissionTo called but not implemented.")
+		return encodableError(fmt.Errorf("API HasPermissionTo called but not implemented."))
 	}
 	return nil
 }
@@ -2193,7 +2207,7 @@ func (s *apiRPCServer) HasPermissionToTeam(args *Z_HasPermissionToTeamArgs, retu
 	}); ok {
 		returns.A = hook.HasPermissionToTeam(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API HasPermissionToTeam called but not implemented.")
+		return encodableError(fmt.Errorf("API HasPermissionToTeam called but not implemented."))
 	}
 	return nil
 }
@@ -2223,7 +2237,7 @@ func (s *apiRPCServer) HasPermissionToChannel(args *Z_HasPermissionToChannelArgs
 	}); ok {
 		returns.A = hook.HasPermissionToChannel(args.A, args.B, args.C)
 	} else {
-		return fmt.Errorf("API HasPermissionToChannel called but not implemented.")
+		return encodableError(fmt.Errorf("API HasPermissionToChannel called but not implemented."))
 	}
 	return nil
 }
@@ -2251,7 +2265,7 @@ func (s *apiRPCServer) LogDebug(args *Z_LogDebugArgs, returns *Z_LogDebugReturns
 	}); ok {
 		hook.LogDebug(args.A, args.B...)
 	} else {
-		return fmt.Errorf("API LogDebug called but not implemented.")
+		return encodableError(fmt.Errorf("API LogDebug called but not implemented."))
 	}
 	return nil
 }
@@ -2279,7 +2293,7 @@ func (s *apiRPCServer) LogInfo(args *Z_LogInfoArgs, returns *Z_LogInfoReturns) e
 	}); ok {
 		hook.LogInfo(args.A, args.B...)
 	} else {
-		return fmt.Errorf("API LogInfo called but not implemented.")
+		return encodableError(fmt.Errorf("API LogInfo called but not implemented."))
 	}
 	return nil
 }
@@ -2307,7 +2321,7 @@ func (s *apiRPCServer) LogError(args *Z_LogErrorArgs, returns *Z_LogErrorReturns
 	}); ok {
 		hook.LogError(args.A, args.B...)
 	} else {
-		return fmt.Errorf("API LogError called but not implemented.")
+		return encodableError(fmt.Errorf("API LogError called but not implemented."))
 	}
 	return nil
 }
@@ -2335,7 +2349,7 @@ func (s *apiRPCServer) LogWarn(args *Z_LogWarnArgs, returns *Z_LogWarnReturns) e
 	}); ok {
 		hook.LogWarn(args.A, args.B...)
 	} else {
-		return fmt.Errorf("API LogWarn called but not implemented.")
+		return encodableError(fmt.Errorf("API LogWarn called but not implemented."))
 	}
 	return nil
 }

plugin/interface_generator/main.go

@@ -69,6 +69,43 @@ func FieldListToNames(fieldList *ast.FieldList, fileset *token.FileSet) string {
 	return strings.Join(result, ", ")
 }
 
+func FieldListToEncodedErrors(structPrefix string, fieldList *ast.FieldList, fileset *token.FileSet) string {
+	result := []string{}
+	if fieldList == nil {
+		return ""
+	}
+
+	nextLetter := 'A'
+	for _, field := range fieldList.List {
+		typeNameBuffer := &bytes.Buffer{}
+		err := printer.Fprint(typeNameBuffer, fileset, field.Type)
+		if err != nil {
+			panic(err)
+		}
+
+		if typeNameBuffer.String() != "error" {
+			nextLetter += 1
+			continue
+		}
+
+		name := ""
+		if len(field.Names) == 0 {
+			name = string(nextLetter)
+			nextLetter += 1
+		} else {
+			for range field.Names {
+				name += string(nextLetter)
+				nextLetter += 1
+			}
+		}
+
+		result = append(result, structPrefix+name+" = encodableError("+structPrefix+name+")")
+
+	}
+
+	return strings.Join(result, "\n")
+}
+
 func FieldListDestruct(structPrefix string, fieldList *ast.FieldList, fileset *token.FileSet) string {
 	result := []string{}
 	if fieldList == nil || len(fieldList.List) == 0 {
@@ -237,8 +274,9 @@ func (s *hooksRPCServer) {{.Name}}(args *{{.Name | obscure}}Args, returns *{{.Na
 		{{.Name}}{{funcStyle .Params}} {{funcStyle .Return}}
 	}); ok {
 		{{if .Return}}{{destruct "returns." .Return}} = {{end}}hook.{{.Name}}({{destruct "args." .Params}})
+		{{if .Return}}{{encodeErrors "returns." .Return}}{{end}}
 	} else {
-		return fmt.Errorf("Hook {{.Name}} called but not implemented.")
+		return encodableError(fmt.Errorf("Hook {{.Name}} called but not implemented."))
 	}
 	return nil
 }
@@ -269,7 +307,7 @@ func (s *apiRPCServer) {{.Name}}(args *{{.Name | obscure}}Args, returns *{{.Name
 	}); ok {
 		{{if .Return}}{{destruct "returns." .Return}} = {{end}}hook.{{.Name}}({{destruct "args." .Params}})
 	} else {
-		return fmt.Errorf("API {{.Name}} called but not implemented.")
+		return encodableError(fmt.Errorf("API {{.Name}} called but not implemented."))
 	}
 	return nil
 }
@@ -292,6 +330,9 @@ func generateGlue(info *PluginInterfaceInfo) {
 		"funcStyle":   func(fields *ast.FieldList) string { return FieldListToFuncList(fields, info.FileSet) },
 		"structStyle": func(fields *ast.FieldList) string { return FieldListToStructList(fields, info.FileSet) },
 		"valuesOnly":  func(fields *ast.FieldList) string { return FieldListToNames(fields, info.FileSet) },
+		"encodeErrors": func(structPrefix string, fields *ast.FieldList) string {
+			return FieldListToEncodedErrors(structPrefix, fields, info.FileSet)
+		},
 		"destruct": func(structPrefix string, fields *ast.FieldList) string {
 			return FieldListDestruct(structPrefix, fields, info.FileSet)
 		},