[MM-54933] Add the ability to @ mention custom groups in group constrained teams and channels (#24987)

* add the ability to @ mention custom groups in group constrained teams
---------
Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/channels/src/packages/mattermost-redux/src/selectors/entities/groups.test.ts

@@ -121,7 +121,7 @@ describe('Selectors.Groups', () => {
             },
             teams: {
                 teams: {
-                    [teamID]: {group_constrained: false},
+                    [teamID]: {group_constrained: true, id: teamID},
                 },
                 groupsAssociatedToTeam: {
                     [teamID]: {ids: teamAssociatedGroupIDs},
@@ -129,7 +129,7 @@ describe('Selectors.Groups', () => {
             },
             channels: {
                 channels: {
-                    [channelID]: {team_id: teamID, id: channelID},
+                    [channelID]: {team_id: teamID, id: channelID, group_constrained: true},
                 },
                 groupsAssociatedToChannel: {
                     [channelID]: {ids: channelAssociatedGroupIDs},
@@ -242,4 +242,38 @@ describe('Selectors.Groups', () => {
         ];
         expect(Selectors.getMyGroupMentionKeysForChannel(testState, teamID, channelID)).toEqual(expected);
     });
+
+    it('getAssociatedGroupsForReference team constrained', () => {
+        const expected = [
+            group5,
+            group1,
+        ];
+        expect(Selectors.getAssociatedGroupsForReference(testState, teamID, '')).toEqual(expected);
+    });
+
+    it('getAssociatedGroupsForReference channel constrained', () => {
+        const expected = [
+            group5,
+            group4,
+        ];
+        expect(Selectors.getAssociatedGroupsForReference(testState, '', channelID)).toEqual(expected);
+    });
+
+    it('getAssociatedGroupsForReference team and channel constrained', () => {
+        const expected = [
+            group4,
+            group1,
+            group5,
+        ];
+        expect(Selectors.getAssociatedGroupsForReference(testState, teamID, channelID)).toEqual(expected);
+    });
+
+    it('getAssociatedGroupsForReference no constraints', () => {
+        const expected = [
+            group1,
+            group4,
+            group5,
+        ];
+        expect(Selectors.getAssociatedGroupsForReference(testState, '', '')).toEqual(expected);
+    });
 });

webapp/channels/src/packages/mattermost-redux/src/selectors/entities/groups.ts

@@ -125,11 +125,16 @@ export function getAssociatedGroupsForReference(state: GlobalState, teamId: stri
     if (team && team.group_constrained && channel && channel.group_constrained) {
         const groupsFromChannel = getGroupsAssociatedToChannelForReference(state, channelId);
         const groupsFromTeam = getGroupsAssociatedToTeamForReference(state, teamId);
-        groupsForReference = groupsFromChannel.concat(groupsFromTeam.filter((item) => groupsFromChannel.indexOf(item) < 0));
+        const customGroups = getAllCustomGroups(state);
+        groupsForReference = groupsFromChannel.concat(groupsFromTeam.filter((item) => groupsFromChannel.indexOf(item) < 0), customGroups);
     } else if (team && team.group_constrained) {
-        groupsForReference = getGroupsAssociatedToTeamForReference(state, teamId);
+        const customGroups = getAllCustomGroups(state);
+        const groupsFromTeam = getGroupsAssociatedToTeamForReference(state, teamId);
+        groupsForReference = [...customGroups, ...groupsFromTeam];
     } else if (channel && channel.group_constrained) {
-        groupsForReference = getGroupsAssociatedToChannelForReference(state, channelId);
+        const customGroups = getAllCustomGroups(state);
+        const groupsFromChannel = getGroupsAssociatedToChannelForReference(state, channelId);
+        groupsForReference = [...customGroups, ...groupsFromChannel];
     } else {
         groupsForReference = getAllAssociatedGroupsForReference(state, false);
     }
@@ -259,6 +264,14 @@ export const getAllGroupsForReferenceByName: (state: GlobalState) => Record<stri
     },
 );
 
+export const getAllCustomGroups: (state: GlobalState) => Group[] = createSelector(
+    'getAllCustomGroups',
+    getAllGroups,
+    (groups) => {
+        return Object.entries(groups).filter((entry) => (entry[1].allow_reference && entry[1].delete_at === 0 && entry[1].source === GroupSource.Custom)).map((entry) => entry[1]);
+    },
+);
+
 export const makeGetMyAllowReferencedGroups = () => {
     return createSelector(
         'makeGetMyAllowReferencedGroups',