MM-24132: Migrate AppError from SaveDirectChannel/channel_store.go (#14318)

* MM-24135: Migrate AppError from SaveChannel/channel_store.go

This is the first POC of migration of store app errors to plain error.

We create a few basic error types in the store package and use
them to return the errors from store methods. In the app layer,
we inspect the error and re-create the exact app errors. This lets
us preserve the same error content, but yet move to plain errors.

Since this is a gradual migration, this means that the error inspection
code will be duplicated across the app layer whenever a store method
is invoked. But all of that should go away once we start propagating
the errors higher up the hierarchy.

There have been a significant amount of changes in the storetest and searchtest
layer, primarily because we have to rename the err variable now that it is of
a different type.

* Addressed review comments

* MM-24132: Migrate AppError from SaveDirectChannel/channel_store.go

This PR migrates 2 new methods SaveDirectChannel and CreateDirectChannel
to return error instead of AppError.

We also need to handle the error internally in SaveMultipleMember for now
until that is migrated too.

* Fix layers

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/channel.go

@@ -336,20 +336,44 @@ func (a *App) createDirectChannel(userId string, otherUserId string) (*model.Cha
 	}
 	otherUser := result.Data.(*model.User)
 
-	channel, err := a.Srv().Store.Channel().CreateDirectChannel(user, otherUser)
+	channel, nErr := a.Srv().Store.Channel().CreateDirectChannel(user, otherUser)
-	if err != nil {
+	if nErr != nil {
-		if err.Id == store.CHANNEL_EXISTS_ERROR {
+		var invErr *store.ErrInvalidInput
-			return channel, err
+		var cErr *store.ErrConflict
+		var ltErr *store.ErrLimitExceeded
+		var appErr *model.AppError
+		switch {
+		case errors.As(nErr, &invErr):
+			switch {
+			case invErr.Entity == "Channel" && invErr.Field == "DeleteAt":
+				return nil, model.NewAppError("CreateChannel", "store.sql_channel.save.archived_channel.app_error", nil, "", http.StatusBadRequest)
+			case invErr.Entity == "Channel" && invErr.Field == "Type":
+				return nil, model.NewAppError("CreateChannel", "store.sql_channel.save_direct_channel.not_direct.app_error", nil, "", http.StatusBadRequest)
+			case invErr.Entity == "Channel" && invErr.Field == "Id":
+				return nil, model.NewAppError("SqlChannelStore.Save", "store.sql_channel.save_channel.existing.app_error", nil, "id="+invErr.Value.(string), http.StatusBadRequest)
+			}
+		case errors.As(nErr, &cErr):
+			switch cErr.Resource {
+			case "Channel":
+				return channel, model.NewAppError("CreateChannel", store.CHANNEL_EXISTS_ERROR, nil, cErr.Error(), http.StatusBadRequest)
+			case "ChannelMembers":
+				return nil, model.NewAppError("CreateChannel", "store.sql_channel.save_member.exists.app_error", nil, cErr.Error(), http.StatusBadRequest)
+			}
+		case errors.As(nErr, &ltErr):
+			return nil, model.NewAppError("CreateChannel", "store.sql_channel.save_channel.limit.app_error", nil, ltErr.Error(), http.StatusBadRequest)
+		case errors.As(nErr, &appErr): // in case we haven't converted to plain error.
+			return nil, appErr
+		default: // last fallback in case it doesn't map to an existing app error.
+			return nil, model.NewAppError("CreateDirectChannel", "app.channel.create_direct_channel.internal_error", nil, nErr.Error(), http.StatusInternalServerError)
 		}
-		return nil, err
 	}
 
-	if err = a.Srv().Store.ChannelMemberHistory().LogJoinEvent(userId, channel.Id, model.GetMillis()); err != nil {
+	if err := a.Srv().Store.ChannelMemberHistory().LogJoinEvent(userId, channel.Id, model.GetMillis()); err != nil {
 		mlog.Error("Failed to update ChannelMemberHistory table", mlog.Err(err))
 		return nil, err
 	}
 	if userId != otherUserId {
-		if err = a.Srv().Store.ChannelMemberHistory().LogJoinEvent(otherUserId, channel.Id, model.GetMillis()); err != nil {
+		if err := a.Srv().Store.ChannelMemberHistory().LogJoinEvent(otherUserId, channel.Id, model.GetMillis()); err != nil {
 			mlog.Error("Failed to update ChannelMemberHistory table", mlog.Err(err))
 			return nil, err
 		}

i18n/en.json

@@ -2938,6 +2938,10 @@
     "id": "app.channel.create_channel.no_team_id.app_error",
     "translation": "Must specify the team ID to create a channel."
   },
+  {
+    "id": "app.channel.create_direct_channel.internal_error",
+    "translation": "Unable to save direct channel."
+  },
   {
     "id": "app.channel.move_channel.members_do_not_match.error",
     "translation": "Unable to move a channel unless all its members are already members of the destination team."
@@ -6062,26 +6066,10 @@
     "id": "store.sql_channel.save_channel.limit.app_error",
     "translation": "You've reached the limit of the number of allowed channels."
   },
-  {
-    "id": "store.sql_channel.save_direct_channel.add_members.app_error",
-    "translation": "Unable to add direct channel members."
-  },
-  {
-    "id": "store.sql_channel.save_direct_channel.commit.app_error",
-    "translation": "Unable to commit transaction."
-  },
-  {
-    "id": "store.sql_channel.save_direct_channel.internal_error",
-    "translation": "Unable to save direct channel."
-  },
   {
     "id": "store.sql_channel.save_direct_channel.not_direct.app_error",
     "translation": "Not a direct channel attempted to be created with SaveDirectChannel."
   },
-  {
-    "id": "store.sql_channel.save_direct_channel.open_transaction.app_error",
-    "translation": "Unable to open transaction."
-  },
   {
     "id": "store.sql_channel.save_member.commit_transaction.app_error",
     "translation": "Unable to commit transaction."
@@ -6094,26 +6082,6 @@
     "id": "store.sql_channel.save_member.open_transaction.app_error",
     "translation": "Unable to open transaction."
   },
-  {
-    "id": "store.sql_channel.save_member.save.app_error",
-    "translation": "Unable to save the channel member."
-  },
-  {
-    "id": "store.sql_channel.save_multimple_members.channel_roles.app_error",
-    "translation": "Unable to build query to get the channel roles."
-  },
-  {
-    "id": "store.sql_channel.save_multimple_members.channel_roles_query.app_error",
-    "translation": "Error fetching the channel roles."
-  },
-  {
-    "id": "store.sql_channel.save_multimple_members.team_roles.app_error",
-    "translation": "Unable to build query to get the team roles."
-  },
-  {
-    "id": "store.sql_channel.save_multimple_members.team_roles_query.app_error",
-    "translation": "Error fetching the team roles."
-  },
   {
     "id": "store.sql_channel.search.app_error",
     "translation": "We encountered an error searching channels."

store/opentracing_layer.go

@@ -594,7 +594,7 @@ func (s *OpenTracingLayerChannelStore) CountPostsAfter(channelId string, timesta
 	return resultVar0, resultVar1
 }
 
-func (s *OpenTracingLayerChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, *model.AppError) {
+func (s *OpenTracingLayerChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, error) {
 	origCtx := s.Root.Store.Context()
 	span, newCtx := tracing.StartSpanWithParentByContext(s.Root.Store.Context(), "ChannelStore.CreateDirectChannel")
 	s.Root.Store.SetContext(newCtx)
@@ -1683,7 +1683,7 @@ func (s *OpenTracingLayerChannelStore) Save(channel *model.Channel, maxChannelsP
 	return resultVar0, resultVar1
 }
 
-func (s *OpenTracingLayerChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, *model.AppError) {
+func (s *OpenTracingLayerChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error) {
 	origCtx := s.Root.Store.Context()
 	span, newCtx := tracing.StartSpanWithParentByContext(s.Root.Store.Context(), "ChannelStore.SaveDirectChannel")
 	s.Root.Store.SetContext(newCtx)

store/searchlayer/channel_layer.go

@@ -97,7 +97,7 @@ func (c *SearchChannelStore) RemoveMember(channelId, userIdToRemove string) *mod
 	return err
 }
 
-func (c *SearchChannelStore) CreateDirectChannel(user *model.User, otherUser *model.User) (*model.Channel, *model.AppError) {
+func (c *SearchChannelStore) CreateDirectChannel(user *model.User, otherUser *model.User) (*model.Channel, error) {
 	channel, err := c.ChannelStore.CreateDirectChannel(user, otherUser)
 	if err == nil {
 		c.rootStore.indexUserFromID(user.Id)

store/sqlstore/channel_store.go

@@ -534,7 +534,7 @@ func (s SqlChannelStore) Save(channel *model.Channel, maxChannelsPerTeam int64)
 	return newChannel, nil
 }
 
-func (s SqlChannelStore) CreateDirectChannel(user *model.User, otherUser *model.User) (*model.Channel, *model.AppError) {
+func (s SqlChannelStore) CreateDirectChannel(user *model.User, otherUser *model.User) (*model.Channel, error) {
 	channel := new(model.Channel)
 
 	channel.DisplayName = ""
@@ -559,74 +559,42 @@ func (s SqlChannelStore) CreateDirectChannel(user *model.User, otherUser *model.
 	return s.SaveDirectChannel(channel, cm1, cm2)
 }
 
-func (s SqlChannelStore) SaveDirectChannel(directchannel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, *model.AppError) {
+func (s SqlChannelStore) SaveDirectChannel(directchannel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error) {
 	if directchannel.DeleteAt != 0 {
-		return nil, model.NewAppError("SqlChannelStore.Save", "store.sql_channel.save.archived_channel.app_error", nil, "", http.StatusBadRequest)
+		return nil, store.NewErrInvalidInput("Channel", "DeleteAt", directchannel.DeleteAt)
 	}
 
 	if directchannel.Type != model.CHANNEL_DIRECT {
-		return nil, model.NewAppError("SqlChannelStore.SaveDirectChannel", "store.sql_channel.save_direct_channel.not_direct.app_error", nil, "", http.StatusBadRequest)
+		return nil, store.NewErrInvalidInput("Channel", "Type", directchannel.Type)
 	}
 
 	transaction, err := s.GetMaster().Begin()
 	if err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveDirectChannel", "store.sql_channel.save_direct_channel.open_transaction.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "begin_transaction")
 	}
 	defer finalizeTransaction(transaction)
 
 	directchannel.TeamId = ""
 	newChannel, err := s.saveChannelT(transaction, directchannel, 0)
 	if err != nil {
-		// TODO: This will go away once SaveDirectChannel returns error
+		return newChannel, err
-		var invErr *store.ErrInvalidInput
-		var cErr *store.ErrConflict
-		var ltErr *store.ErrLimitExceeded
-		var appErr *model.AppError
-		if errors.As(err, &invErr) {
-			if invErr.Entity == "Channel" && invErr.Field == "DeleteAt" {
-				return newChannel, model.NewAppError("CreateChannel", "store.sql_channel.save.archived_channel.app_error", nil, "", http.StatusBadRequest)
-			}
-			if invErr.Entity == "Channel" && invErr.Field == "Type" {
-				return newChannel, model.NewAppError("CreateChannel", "store.sql_channel.save.direct_channel.app_error", nil, "", http.StatusBadRequest)
-			}
-			if invErr.Entity == "Channel" && invErr.Field == "Id" {
-				return newChannel, model.NewAppError("SqlChannelStore.Save", "store.sql_channel.save_channel.existing.app_error", nil, "id="+invErr.Value.(string), http.StatusBadRequest)
-			}
-		}
-		if errors.As(err, &cErr) {
-			if cErr.Resource == "Channel" {
-				return newChannel, model.NewAppError("CreateChannel", store.CHANNEL_EXISTS_ERROR, nil, cErr.Error(), http.StatusBadRequest)
-			}
-		}
-		if errors.As(err, &ltErr) {
-			if ltErr.What == "channels_per_team" {
-				return newChannel, model.NewAppError("CreateChannel", "store.sql_channel.save_channel.limit.app_error", nil, ltErr.Error(), http.StatusBadRequest)
-			}
-		}
-		if errors.As(err, &appErr) {
-			return nil, appErr
-		} else {
-			return nil, model.NewAppError("SqlChannelStore.SaveDirectChannel", "store.sql_channel.save_direct_channel.internal_error", nil, err.Error(), http.StatusInternalServerError)
-		}
 	}
 
 	// Members need new channel ID
 	member1.ChannelId = newChannel.Id
 	member2.ChannelId = newChannel.Id
 
-	var memberSaveErr *model.AppError
 	if member1.UserId != member2.UserId {
-		_, memberSaveErr = s.saveMultipleMembersT(transaction, []*model.ChannelMember{member1, member2})
+		_, err = s.saveMultipleMembersT(transaction, []*model.ChannelMember{member1, member2})
 	} else {
-		_, memberSaveErr = s.saveMemberT(transaction, member2)
+		_, err = s.saveMemberT(transaction, member2)
 	}
-
+	if err != nil {
-	if memberSaveErr != nil {
+		return nil, err
-		return nil, model.NewAppError("SqlChannelStore.SaveDirectChannel", "store.sql_channel.save_direct_channel.add_members.app_error", nil, memberSaveErr.Error(), http.StatusInternalServerError)
 	}
 
 	if err := transaction.Commit(); err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveDirectChannel", "store.sql_channel.save_direct_channel.commit.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "commit_transaction")
 	}
 
 	return newChannel, nil
@@ -639,7 +607,7 @@ func (s SqlChannelStore) saveChannelT(transaction *gorp.Transaction, channel *mo
 	}
 
 	channel.PreSave()
-	if err := channel.IsValid(); err != nil { // TODO: this needs to return plain error
+	if err := channel.IsValid(); err != nil { // TODO: this needs to return plain error in v6.
 		return nil, err // we just pass through the error as-is for now.
 	}
 
@@ -1345,9 +1313,21 @@ func (s SqlChannelStore) SaveMultipleMembers(members []*model.ChannelMember) ([]
 	}
 	defer finalizeTransaction(transaction)
 
-	newMembers, appErr := s.saveMultipleMembersT(transaction, members)
+	newMembers, err := s.saveMultipleMembersT(transaction, members)
-	if appErr != nil {
+	if err != nil { // TODO: this will go away once SaveMultipleMembers is migrated too.
-		return nil, appErr
+		var cErr *store.ErrConflict
+		var appErr *model.AppError
+		switch {
+		case errors.As(err, &cErr):
+			switch cErr.Resource {
+			case "ChannelMembers":
+				return nil, model.NewAppError("CreateChannel", "store.sql_channel.save_member.exists.app_error", nil, cErr.Error(), http.StatusBadRequest)
+			}
+		case errors.As(err, &appErr): // in case we haven't converted to plain error.
+			return nil, appErr
+		default: // last fallback in case it doesn't map to an existing app error.
+			return nil, model.NewAppError("CreateDirectChannel", "app.channel.create_direct_channel.internal_error", nil, err.Error(), http.StatusInternalServerError)
+		}
 	}
 
 	if err := transaction.Commit(); err != nil {
@@ -1365,7 +1345,7 @@ func (s SqlChannelStore) SaveMember(member *model.ChannelMember) (*model.Channel
 	return newMembers[0], nil
 }
 
-func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, members []*model.ChannelMember) ([]*model.ChannelMember, *model.AppError) {
+func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, members []*model.ChannelMember) ([]*model.ChannelMember, error) {
 	newChannelMembers := map[string]int{}
 	users := map[string]bool{}
 	for _, member := range members {
@@ -1377,7 +1357,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 		users[member.UserId] = true
 
 		member.PreSave()
-		if err := member.IsValid(); err != nil {
+		if err := member.IsValid(); err != nil { // TODO: this needs to return plain error in v6.
 			return nil, err
 		}
 	}
@@ -1407,7 +1387,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 
 	channelRolesSql, channelRolesArgs, err := channelRolesQuery.ToSql()
 	if err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveMultipleMembers", "store.sql_channel.save_multimple_members.channel_roles.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "channel_roles_tosql")
 	}
 
 	var defaultChannelsRoles []struct {
@@ -1418,7 +1398,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 	}
 	_, err = s.GetMaster().Select(&defaultChannelsRoles, channelRolesSql, channelRolesArgs...)
 	if err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveMultipleMembers", "store.sql_channel.save_multimple_members.channel_roles_query.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "default_channel_roles_select")
 	}
 
 	for _, defaultRoles := range defaultChannelsRoles {
@@ -1446,7 +1426,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 
 	teamRolesSql, teamRolesArgs, err := teamRolesQuery.ToSql()
 	if err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveMultipleMembers", "store.sql_channel.save_multimple_members.team_roles.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "team_roles_tosql")
 	}
 
 	var defaultTeamsRoles []struct {
@@ -1457,7 +1437,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 	}
 	_, err = s.GetMaster().Select(&defaultTeamsRoles, teamRolesSql, teamRolesArgs...)
 	if err != nil {
-		return nil, model.NewAppError("SqlChannelStore.SaveMultipleMembers", "store.sql_channel.save_multimple_members.team_roles_query.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "default_team_roles_select")
 	}
 
 	for _, defaultRoles := range defaultTeamsRoles {
@@ -1471,14 +1451,14 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 
 	sql, args, err := query.ToSql()
 	if err != nil {
-		return nil, model.NewAppError("SqlTeamStore.SaveMember", "store.sql_channel.save_member.save.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "channel_members_tosql")
 	}
 
 	if _, err := s.GetMaster().Exec(sql, args...); err != nil {
 		if IsUniqueConstraintError(err, []string{"ChannelId", "channelmembers_pkey", "PRIMARY"}) {
-			return nil, model.NewAppError("SqlTeamStore.SaveMember", "store.sql_channel.save_member.exists.app_error", nil, err.Error(), http.StatusBadRequest)
+			return nil, store.NewErrConflict("ChannelMembers", err, "")
 		}
-		return nil, model.NewAppError("SqlTeamStore.SaveMember", "store.sql_channel.save_member.save.app_error", nil, err.Error(), http.StatusInternalServerError)
+		return nil, errors.Wrap(err, "channel_members_save")
 	}
 
 	newMembers := []*model.ChannelMember{}
@@ -1506,7 +1486,7 @@ func (s SqlChannelStore) saveMultipleMembersT(transaction *gorp.Transaction, mem
 	return newMembers, nil
 }
 
-func (s SqlChannelStore) saveMemberT(transaction *gorp.Transaction, member *model.ChannelMember) (*model.ChannelMember, *model.AppError) {
+func (s SqlChannelStore) saveMemberT(transaction *gorp.Transaction, member *model.ChannelMember) (*model.ChannelMember, error) {
 	members, err := s.saveMultipleMembersT(transaction, []*model.ChannelMember{member})
 	if err != nil {
 		return nil, err

store/store.go

@@ -128,8 +128,8 @@ type TeamStore interface {
 
 type ChannelStore interface {
 	Save(channel *model.Channel, maxChannelsPerTeam int64) (*model.Channel, error)
-	CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, *model.AppError)
+	CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, error)
-	SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, *model.AppError)
+	SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error)
 	Update(channel *model.Channel) (*model.Channel, *model.AppError)
 	Get(id string, allowFromCache bool) (*model.Channel, *model.AppError)
 	InvalidateChannel(id string)

store/storetest/channel_store.go

@@ -185,15 +185,15 @@ func testChannelStoreSaveDirectChannel(t *testing.T, ss store.Store, s SqlSuppli
 	m2.UserId = u2.Id
 	m2.NotifyProps = model.GetDefaultChannelNotifyProps()
 
-	_, err = ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
+	_, nErr := ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
-	require.Nil(t, err, "couldn't save direct channel", err)
+	require.Nil(t, nErr, "couldn't save direct channel", nErr)
 
 	members, err := ss.Channel().GetMembers(o1.Id, 0, 100)
 	require.Nil(t, err)
 	require.Len(t, *members, 2, "should have saved 2 members")
 
-	_, err = ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
+	_, nErr = ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
-	require.NotNil(t, err, "shoudn't be a able to update from save")
+	require.NotNil(t, nErr, "shoudn't be a able to update from save")
 
 	// Attempt to save a direct channel that already exists
 	o1a := model.Channel{
@@ -203,25 +203,26 @@ func testChannelStoreSaveDirectChannel(t *testing.T, ss store.Store, s SqlSuppli
 		Type:        o1.Type,
 	}
 
-	returnedChannel, err := ss.Channel().SaveDirectChannel(&o1a, &m1, &m2)
+	returnedChannel, nErr := ss.Channel().SaveDirectChannel(&o1a, &m1, &m2)
-	require.NotNil(t, err, "should've failed to save a duplicate direct channel")
+	require.NotNil(t, nErr, "should've failed to save a duplicate direct channel")
-	require.Equal(t, store.CHANNEL_EXISTS_ERROR, err.Id, "should've returned CHANNEL_EXISTS_ERROR")
+	var cErr *store.ErrConflict
+	require.Truef(t, errors.As(nErr, &cErr), "should've returned CHANNEL_EXISTS_ERROR")
 	require.Equal(t, o1.Id, returnedChannel.Id, "should've failed to save a duplicate direct channel")
 
 	// Attempt to save a non-direct channel
 	o1.Id = ""
 	o1.Name = "zz" + model.NewId() + "b"
 	o1.Type = model.CHANNEL_OPEN
-	_, err = ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
+	_, nErr = ss.Channel().SaveDirectChannel(&o1, &m1, &m2)
-	require.NotNil(t, err, "Should not be able to save non-direct channel")
+	require.NotNil(t, nErr, "Should not be able to save non-direct channel")
 
 	// Save yourself Direct Message
 	o1.Id = ""
 	o1.DisplayName = "Myself"
 	o1.Name = "zz" + model.NewId() + "b"
 	o1.Type = model.CHANNEL_DIRECT
-	_, err = ss.Channel().SaveDirectChannel(&o1, &m1, &m1)
+	_, nErr = ss.Channel().SaveDirectChannel(&o1, &m1, &m1)
-	require.Nil(t, err, "couldn't save direct channel", err)
+	require.Nil(t, nErr, "couldn't save direct channel", nErr)
 
 	members, err = ss.Channel().GetMembers(o1.Id, 0, 100)
 	require.Nil(t, err)
@@ -248,8 +249,8 @@ func testChannelStoreCreateDirectChannel(t *testing.T, ss store.Store) {
 	_, err = ss.Team().SaveMember(&model.TeamMember{TeamId: model.NewId(), UserId: u2.Id}, -1)
 	require.Nil(t, err)
 
-	c1, err := ss.Channel().CreateDirectChannel(u1, u2)
+	c1, nErr := ss.Channel().CreateDirectChannel(u1, u2)
-	require.Nil(t, err, "couldn't create direct channel", err)
+	require.Nil(t, nErr, "couldn't create direct channel", nErr)
 	defer func() {
 		ss.Channel().PermanentDeleteMembersByChannel(c1.Id)
 		ss.Channel().PermanentDelete(c1.Id)
@@ -402,8 +403,8 @@ func testChannelStoreGet(t *testing.T, ss store.Store, s SqlSupplier) {
 	m2.UserId = u2.Id
 	m2.NotifyProps = model.GetDefaultChannelNotifyProps()
 
-	_, err = ss.Channel().SaveDirectChannel(&o2, &m1, &m2)
+	_, nErr = ss.Channel().SaveDirectChannel(&o2, &m1, &m2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 
 	c2, err := ss.Channel().Get(o2.Id, false)
 	require.Nil(t, err, err)
@@ -478,8 +479,8 @@ func testChannelStoreGetChannelsByIds(t *testing.T, ss store.Store) {
 	m2.UserId = u2.Id
 	m2.NotifyProps = model.GetDefaultChannelNotifyProps()
 
-	_, err = ss.Channel().SaveDirectChannel(&o2, &m1, &m2)
+	_, nErr = ss.Channel().SaveDirectChannel(&o2, &m1, &m2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 
 	t.Run("Get 2 existing channels", func(t *testing.T) {
 		r1, err := ss.Channel().GetChannelsByIds([]string{o1.Id, o2.Id}, false)
@@ -3235,8 +3236,8 @@ func testChannelStoreGetAllChannels(t *testing.T, ss store.Store, s SqlSupplier)
 
 	u1 := model.User{Id: model.NewId()}
 	u2 := model.User{Id: model.NewId()}
-	_, err = ss.Channel().CreateDirectChannel(&u1, &u2)
+	_, nErr = ss.Channel().CreateDirectChannel(&u1, &u2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 
 	userIds := []string{model.NewId(), model.NewId(), model.NewId()}
 
@@ -3711,13 +3712,13 @@ func testChannelStoreGetMembersForUser(t *testing.T, ss store.Store) {
 		u2 := model.User{Id: model.NewId()}
 		u3 := model.User{Id: model.NewId()}
 		u4 := model.User{Id: model.NewId()}
-		_, err = ss.Channel().CreateDirectChannel(&u1, &user)
+		_, nErr = ss.Channel().CreateDirectChannel(&u1, &user)
-		require.Nil(t, err)
+		require.Nil(t, nErr)
-		_, err = ss.Channel().CreateDirectChannel(&u2, &user)
+		_, nErr = ss.Channel().CreateDirectChannel(&u2, &user)
-		require.Nil(t, err)
+		require.Nil(t, nErr)
 		// other user direct message
-		_, err = ss.Channel().CreateDirectChannel(&u3, &u4)
+		_, nErr = ss.Channel().CreateDirectChannel(&u3, &u4)
-		require.Nil(t, err)
+		require.Nil(t, nErr)
 
 		var members *model.ChannelMembers
 		members, err = ss.Channel().GetMembersForUser(o1.TeamId, m1.UserId)
@@ -5502,8 +5503,8 @@ func testChannelStoreAnalyticsDeletedTypeCount(t *testing.T, ss store.Store) {
 	_, err = ss.User().Save(u2)
 	require.Nil(t, err)
 
-	d4, err := ss.Channel().CreateDirectChannel(u1, u2)
+	d4, nErr := ss.Channel().CreateDirectChannel(u1, u2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 	defer func() {
 		ss.Channel().PermanentDeleteMembersByChannel(d4.Id)
 		ss.Channel().PermanentDelete(d4.Id)

store/storetest/compliance_store.go

@@ -239,8 +239,8 @@ func testComplianceExportDirectMessages(t *testing.T, ss store.Store) {
 	c1, nErr := ss.Channel().Save(c1, -1)
 	require.Nil(t, nErr)
 
-	cDM, err := ss.Channel().CreateDirectChannel(u1, u2)
+	cDM, nErr := ss.Channel().CreateDirectChannel(u1, u2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 	o1 := &model.Post{}
 	o1.ChannelId = c1.Id
 	o1.UserId = u1.Id
@@ -546,8 +546,8 @@ func testMessageExportDirectMessageChannel(t *testing.T, ss store.Store) {
 	require.Nil(t, err)
 
 	// as well as a DM channel between those users
-	directMessageChannel, err := ss.Channel().CreateDirectChannel(user1, user2)
+	directMessageChannel, nErr := ss.Channel().CreateDirectChannel(user1, user2)
-	require.Nil(t, err)
+	require.Nil(t, nErr)
 
 	// user1 also sends a DM to user2
 	post := &model.Post{

store/storetest/mocks/ChannelStore.go

@@ -156,7 +156,7 @@ func (_m *ChannelStore) CountPostsAfter(channelId string, timestamp int64, userI
 }
 
 // CreateDirectChannel provides a mock function with given fields: userId, otherUserId
-func (_m *ChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, *model.AppError) {
+func (_m *ChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, error) {
 	ret := _m.Called(userId, otherUserId)
 
 	var r0 *model.Channel
@@ -168,13 +168,11 @@ func (_m *ChannelStore) CreateDirectChannel(userId *model.User, otherUserId *mod
 		}
 	}
 
-	var r1 *model.AppError
+	var r1 error
-	if rf, ok := ret.Get(1).(func(*model.User, *model.User) *model.AppError); ok {
+	if rf, ok := ret.Get(1).(func(*model.User, *model.User) error); ok {
 		r1 = rf(userId, otherUserId)
 	} else {
-		if ret.Get(1) != nil {
+		r1 = ret.Error(1)
-			r1 = ret.Get(1).(*model.AppError)
-		}
 	}
 
 	return r0, r1
@@ -1447,7 +1445,7 @@ func (_m *ChannelStore) Save(channel *model.Channel, maxChannelsPerTeam int64) (
 }
 
 // SaveDirectChannel provides a mock function with given fields: channel, member1, member2
-func (_m *ChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, *model.AppError) {
+func (_m *ChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error) {
 	ret := _m.Called(channel, member1, member2)
 
 	var r0 *model.Channel
@@ -1459,13 +1457,11 @@ func (_m *ChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model
 		}
 	}
 
-	var r1 *model.AppError
+	var r1 error
-	if rf, ok := ret.Get(1).(func(*model.Channel, *model.ChannelMember, *model.ChannelMember) *model.AppError); ok {
+	if rf, ok := ret.Get(1).(func(*model.Channel, *model.ChannelMember, *model.ChannelMember) error); ok {
 		r1 = rf(channel, member1, member2)
 	} else {
-		if ret.Get(1) != nil {
+		r1 = ret.Error(1)
-			r1 = ret.Get(1).(*model.AppError)
-		}
 	}
 
 	return r0, r1

store/storetest/user_store.go

@@ -1971,8 +1971,8 @@ func testUserUnreadCount(t *testing.T, ss store.Store) {
 	m1.ChannelId = c2.Id
 	m2.ChannelId = c2.Id
 
-	_, err = ss.Channel().SaveDirectChannel(&c2, &m1, &m2)
+	_, nErr = ss.Channel().SaveDirectChannel(&c2, &m1, &m2)
-	require.Nil(t, err, "couldn't save direct channel")
+	require.Nil(t, nErr, "couldn't save direct channel")
 
 	p1 := model.Post{}
 	p1.ChannelId = c1.Id

store/timer_layer.go

@@ -568,7 +568,7 @@ func (s *TimerLayerChannelStore) CountPostsAfter(channelId string, timestamp int
 	return resultVar0, resultVar1
 }
 
-func (s *TimerLayerChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, *model.AppError) {
+func (s *TimerLayerChannelStore) CreateDirectChannel(userId *model.User, otherUserId *model.User) (*model.Channel, error) {
 	start := timemodule.Now()
 
 	resultVar0, resultVar1 := s.ChannelStore.CreateDirectChannel(userId, otherUserId)
@@ -1569,7 +1569,7 @@ func (s *TimerLayerChannelStore) Save(channel *model.Channel, maxChannelsPerTeam
 	return resultVar0, resultVar1
 }
 
-func (s *TimerLayerChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, *model.AppError) {
+func (s *TimerLayerChannelStore) SaveDirectChannel(channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error) {
 	start := timemodule.Now()
 
 	resultVar0, resultVar1 := s.ChannelStore.SaveDirectChannel(channel, member1, member2)