MM-10833: send down computed channel props (#8953)

* MM-10833: send down computed channel props

This allows channel headers to reference channel mentions for a client
that doesn't already know about the channels in question.

We intentionally don't send down the props for the autocomplete and
search endpoints since they aren't used in that context, and would add
unnecessary overhead.

* update channel props on patch

* revert to treating channel purpose as plaintext

2 files changed, 270 insertions, 0 deletions

diff --git a/app/channel.go b/app/channel.go
index 7394d813b..eee27a6de 100644
--- a/app/channel.go
+++ b/app/channel.go
@@ -1591,3 +1591,67 @@ func (a *App) ToggleMuteChannel(channelId string, userId string) *model.ChannelM
 	a.Srv.Store.Channel().UpdateMember(member)
 	return member
 }
+
+func (a *App) FillInChannelProps(channel *model.Channel) *model.AppError {
+	return a.FillInChannelsProps(&model.ChannelList{channel})
+}
+
+func (a *App) FillInChannelsProps(channelList *model.ChannelList) *model.AppError {
+	// Group the channels by team and call GetChannelsByNames just once per team.
+	channelsByTeam := make(map[string]model.ChannelList)
+	for _, channel := range *channelList {
+		channelsByTeam[channel.TeamId] = append(channelsByTeam[channel.TeamId], channel)
+	}
+
+	for teamId, channelList := range channelsByTeam {
+		allChannelMentions := make(map[string]bool)
+		channelMentions := make(map[*model.Channel][]string, len(channelList))
+
+		// Collect mentions across the channels so as to query just once for this team.
+		for _, channel := range channelList {
+			channelMentions[channel] = model.ChannelMentions(channel.Header)
+
+			for _, channelMention := range channelMentions[channel] {
+				allChannelMentions[channelMention] = true
+			}
+		}
+
+		allChannelMentionNames := make([]string, 0, len(allChannelMentions))
+		for channelName := range allChannelMentions {
+			allChannelMentionNames = append(allChannelMentionNames, channelName)
+		}
+
+		if len(allChannelMentionNames) > 0 {
+			mentionedChannels, err := a.GetChannelsByNames(allChannelMentionNames, teamId)
+			if err != nil {
+				return err
+			}
+
+			mentionedChannelsByName := make(map[string]*model.Channel)
+			for _, channel := range mentionedChannels {
+				mentionedChannelsByName[channel.Name] = channel
+			}
+
+			for _, channel := range channelList {
+				channelMentionsProp := make(map[string]interface{}, len(channelMentions[channel]))
+				for _, channelMention := range channelMentions[channel] {
+					if mentioned, ok := mentionedChannelsByName[channelMention]; ok {
+						if mentioned.Type == model.CHANNEL_OPEN {
+							channelMentionsProp[mentioned.Name] = map[string]interface{}{
+								"display_name": mentioned.DisplayName,
+							}
+						}
+					}
+				}
+
+				if len(channelMentionsProp) > 0 {
+					channel.AddProp("channel_mentions", channelMentionsProp)
+				} else if channel.Props != nil {
+					delete(channel.Props, "channel_mentions")
+				}
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/app/channel_test.go b/app/channel_test.go
index 336d9b25b..4e6aaaf52 100644
--- a/app/channel_test.go
+++ b/app/channel_test.go
@@ -9,6 +9,7 @@ import (
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/store"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestPermanentDeleteChannel(t *testing.T) {
@@ -399,3 +400,208 @@ func TestAppUpdateChannelScheme(t *testing.T) {
 		t.Fatal("Wrong Channel SchemeId")
 	}
 }
+
+func TestFillInChannelProps(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	channelPublic1, err := th.App.CreateChannel(&model.Channel{DisplayName: "Public 1", Name: "public1", Type: model.CHANNEL_OPEN, TeamId: th.BasicTeam.Id}, false)
+	require.Nil(t, err)
+	defer th.App.PermanentDeleteChannel(channelPublic1)
+
+	channelPublic2, err := th.App.CreateChannel(&model.Channel{DisplayName: "Public 2", Name: "public2", Type: model.CHANNEL_OPEN, TeamId: th.BasicTeam.Id}, false)
+	require.Nil(t, err)
+	defer th.App.PermanentDeleteChannel(channelPublic2)
+
+	channelPrivate, err := th.App.CreateChannel(&model.Channel{DisplayName: "Private", Name: "private", Type: model.CHANNEL_PRIVATE, TeamId: th.BasicTeam.Id}, false)
+	require.Nil(t, err)
+	defer th.App.PermanentDeleteChannel(channelPrivate)
+
+	otherTeamId := model.NewId()
+	otherTeam := &model.Team{
+		DisplayName: "dn_" + otherTeamId,
+		Name:        "name" + otherTeamId,
+		Email:       "success+" + otherTeamId + "@simulator.amazonses.com",
+		Type:        model.TEAM_OPEN,
+	}
+	otherTeam, err = th.App.CreateTeam(otherTeam)
+	require.Nil(t, err)
+	defer th.App.PermanentDeleteTeam(otherTeam)
+
+	channelOtherTeam, err := th.App.CreateChannel(&model.Channel{DisplayName: "Other Team Channel", Name: "other-team", Type: model.CHANNEL_OPEN, TeamId: otherTeam.Id}, false)
+	require.Nil(t, err)
+	defer th.App.PermanentDeleteChannel(channelOtherTeam)
+
+	// Note that purpose is intentionally plaintext below.
+
+	t.Run("single channels", func(t *testing.T) {
+		testCases := []struct {
+			Description          string
+			Channel              *model.Channel
+			ExpectedChannelProps map[string]interface{}
+		}{
+			{
+				"channel on basic team without references",
+				&model.Channel{
+					TeamId:  th.BasicTeam.Id,
+					Header:  "No references",
+					Purpose: "No references",
+				},
+				nil,
+			},
+			{
+				"channel on basic team",
+				&model.Channel{
+					TeamId:  th.BasicTeam.Id,
+					Header:  "~public1, ~private, ~other-team",
+					Purpose: "~public2, ~private, ~other-team",
+				},
+				map[string]interface{}{
+					"channel_mentions": map[string]interface{}{
+						"public1": map[string]interface{}{
+							"display_name": "Public 1",
+						},
+					},
+				},
+			},
+			{
+				"channel on other team",
+				&model.Channel{
+					TeamId:  otherTeam.Id,
+					Header:  "~public1, ~private, ~other-team",
+					Purpose: "~public2, ~private, ~other-team",
+				},
+				map[string]interface{}{
+					"channel_mentions": map[string]interface{}{
+						"other-team": map[string]interface{}{
+							"display_name": "Other Team Channel",
+						},
+					},
+				},
+			},
+		}
+
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				err = th.App.FillInChannelProps(testCase.Channel)
+				require.Nil(t, err)
+
+				assert.Equal(t, testCase.ExpectedChannelProps, testCase.Channel.Props)
+			})
+		}
+	})
+
+	t.Run("multiple channels", func(t *testing.T) {
+		testCases := []struct {
+			Description          string
+			Channels             *model.ChannelList
+			ExpectedChannelProps map[string]interface{}
+		}{
+			{
+				"single channel on basic team",
+				&model.ChannelList{
+					{
+						Name:    "test",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "~public1, ~private, ~other-team",
+						Purpose: "~public2, ~private, ~other-team",
+					},
+				},
+				map[string]interface{}{
+					"test": map[string]interface{}{
+						"channel_mentions": map[string]interface{}{
+							"public1": map[string]interface{}{
+								"display_name": "Public 1",
+							},
+						},
+					},
+				},
+			},
+			{
+				"multiple channels on basic team",
+				&model.ChannelList{
+					{
+						Name:    "test",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "~public1, ~private, ~other-team",
+						Purpose: "~public2, ~private, ~other-team",
+					},
+					{
+						Name:    "test2",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "~private, ~other-team",
+						Purpose: "~public2, ~private, ~other-team",
+					},
+					{
+						Name:    "test3",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "No references",
+						Purpose: "No references",
+					},
+				},
+				map[string]interface{}{
+					"test": map[string]interface{}{
+						"channel_mentions": map[string]interface{}{
+							"public1": map[string]interface{}{
+								"display_name": "Public 1",
+							},
+						},
+					},
+					"test2": map[string]interface{}(nil),
+					"test3": map[string]interface{}(nil),
+				},
+			},
+			{
+				"multiple channels across teams",
+				&model.ChannelList{
+					{
+						Name:    "test",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "~public1, ~private, ~other-team",
+						Purpose: "~public2, ~private, ~other-team",
+					},
+					{
+						Name:    "test2",
+						TeamId:  otherTeam.Id,
+						Header:  "~private, ~other-team",
+						Purpose: "~public2, ~private, ~other-team",
+					},
+					{
+						Name:    "test3",
+						TeamId:  th.BasicTeam.Id,
+						Header:  "No references",
+						Purpose: "No references",
+					},
+				},
+				map[string]interface{}{
+					"test": map[string]interface{}{
+						"channel_mentions": map[string]interface{}{
+							"public1": map[string]interface{}{
+								"display_name": "Public 1",
+							},
+						},
+					},
+					"test2": map[string]interface{}{
+						"channel_mentions": map[string]interface{}{
+							"other-team": map[string]interface{}{
+								"display_name": "Other Team Channel",
+							},
+						},
+					},
+					"test3": map[string]interface{}(nil),
+				},
+			},
+		}
+
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				err = th.App.FillInChannelsProps(testCase.Channels)
+				require.Nil(t, err)
+
+				for _, channel := range *testCase.Channels {
+					assert.Equal(t, testCase.ExpectedChannelProps[channel.Name], channel.Props)
+				}
+			})
+		}
+	})
+}