MM-60171: Using a generic function to allocate values (#28245)

We sprinkle a bit of generic magic to refactor a lot
of duplicate code.

To avoid exposing unnecessary code, I duplicated the function
twice. But let me know if you have strong opinions about this.

https://mattermost.atlassian.net/browse/MM-60171

```release-note
NONE
```


---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/session.go

@@ -63,14 +63,9 @@ func (ps *PlatformService) ClearUserSessionCacheLocal(userID string) {
 			return nil
 		}
 
-		toPass := make([]any, 0, len(keys))
-		for i := 0; i < len(keys); i++ {
-			// This always needs to be a pointer to a value.
-			// Otherwise the msp unmarshaler will fail to work.
-			var session model.Session
-			toPass = append(toPass, &session)
-		}
-
+		// This always needs to be model.Session, not *model.Session.
+		// Otherwise the msp unmarshaler will fail to work.
+		toPass := allocateCacheTargets[model.Session](len(keys))
 		errs := ps.sessionCache.GetMulti(keys, toPass)
 		for i, err := range errs {
 			if err != nil {

server/channels/app/platform/status.go

@@ -46,11 +46,7 @@ func (ps *PlatformService) GetAllStatuses() map[string]*model.Status {
 			return nil
 		}
 
-		toPass := make([]any, 0, len(keys))
-		for i := 0; i < len(keys); i++ {
-			var status *model.Status
-			toPass = append(toPass, &status)
-		}
+		toPass := allocateCacheTargets[*model.Status](len(keys))
 		errs := ps.statusCache.GetMulti(keys, toPass)
 		for i, err := range errs {
 			if err != nil {
@@ -84,11 +80,7 @@ func (ps *PlatformService) GetStatusesByIds(userIDs []string) (map[string]any, *
 	metrics := ps.Metrics()
 	missingUserIds := []string{}
 
-	toPass := make([]any, 0, len(userIDs))
-	for i := 0; i < len(userIDs); i++ {
-		var status *model.Status
-		toPass = append(toPass, &status)
-	}
+	toPass := allocateCacheTargets[*model.Status](len(userIDs))
 	// First, we do a GetMulti to get all the status objects.
 	errs := ps.statusCache.GetMulti(userIDs, toPass)
 	for i, err := range errs {
@@ -147,11 +139,7 @@ func (ps *PlatformService) GetUserStatusesByIds(userIDs []string) ([]*model.Stat
 	metrics := ps.Metrics()
 
 	missingUserIds := []string{}
-	toPass := make([]any, 0, len(userIDs))
-	for i := 0; i < len(userIDs); i++ {
-		var status *model.Status
-		toPass = append(toPass, &status)
-	}
+	toPass := allocateCacheTargets[*model.Status](len(userIDs))
 	// First, we do a GetMulti to get all the status objects.
 	errs := ps.statusCache.GetMulti(userIDs, toPass)
 	for i, err := range errs {

server/channels/app/platform/utils.go

@@ -20,3 +20,13 @@ func maxInt(a, b int) int {
 	}
 	return b
 }
+
+// allocateCacheTargets is used to fill target value types
+// for getting items from cache.
+func allocateCacheTargets[T any](l int) []any {
+	toPass := make([]any, 0, l)
+	for i := 0; i < l; i++ {
+		toPass = append(toPass, new(T))
+	}
+	return toPass
+}

server/channels/store/localcachelayer/channel_layer.go

@@ -245,12 +245,7 @@ func (s LocalCacheChannelStore) GetMany(ids []string, allowFromCache bool) (mode
 	var channelsToQuery []string
 
 	if allowFromCache {
-		var toPass []any
-		for i := 0; i < len(ids); i++ {
-			var channel *model.Channel
-			toPass = append(toPass, &channel)
-		}
-
+		toPass := allocateCacheTargets[*model.Channel](len(ids))
 		errs := s.rootStore.doMultiReadCache(s.rootStore.roleCache, ids, toPass)
 		for i, err := range errs {
 			if err != nil {
@@ -352,12 +347,7 @@ func (s LocalCacheChannelStore) getByNames(teamId string, names []string, allowF
 			newKeys = append(newKeys, teamId+name)
 		}
 
-		toPass := make([]any, 0, len(newKeys))
-		for i := 0; i < len(newKeys); i++ {
-			var channel *model.Channel
-			toPass = append(toPass, &channel)
-		}
-
+		toPass := allocateCacheTargets[*model.Channel](len(newKeys))
 		errs := s.rootStore.doMultiReadCache(s.rootStore.roleCache, newKeys, toPass)
 		for i, err := range errs {
 			if err != nil {
@@ -474,12 +464,7 @@ func (s LocalCacheChannelStore) GetChannelsMemberCount(channelIDs []string) (_ m
 	counts := make(map[string]int64)
 	remainingChannels := make([]string, 0)
 
-	toPass := make([]any, 0, len(channelIDs))
-	for i := 0; i < len(channelIDs); i++ {
-		var cacheItem int64
-		toPass = append(toPass, &cacheItem)
-	}
-
+	toPass := allocateCacheTargets[int64](len(channelIDs))
 	errs := s.rootStore.doMultiReadCache(s.rootStore.reaction.rootStore.channelMemberCountsCache, channelIDs, toPass)
 	for i, err := range errs {
 		if err != nil {

server/channels/store/localcachelayer/layer.go

@@ -579,3 +579,13 @@ func (s *LocalCacheStore) Invalidate() {
 	s.doClearCacheCluster(s.teamAllTeamIdsForUserCache)
 	s.doClearCacheCluster(s.rolePermissionsCache)
 }
+
+// allocateCacheTargets is used to fill target value types
+// for getting items from cache.
+func allocateCacheTargets[T any](l int) []any {
+	toPass := make([]any, 0, l)
+	for i := 0; i < l; i++ {
+		toPass = append(toPass, new(T))
+	}
+	return toPass
+}

server/channels/store/localcachelayer/role_layer.go

@@ -62,11 +62,7 @@ func (s LocalCacheRoleStore) GetByNames(names []string) ([]*model.Role, error) {
 	var foundRoles []*model.Role
 	var rolesToQuery []string
 
-	toPass := make([]any, 0, len(names))
-	for i := 0; i < len(names); i++ {
-		var role *model.Role
-		toPass = append(toPass, &role)
-	}
+	toPass := allocateCacheTargets[*model.Role](len(names))
 	errs := s.rootStore.doMultiReadCache(s.rootStore.roleCache, names, toPass)
 	for i, err := range errs {
 		if err != nil {

server/channels/store/localcachelayer/user_layer.go

@@ -82,11 +82,7 @@ func (s *LocalCacheUserStore) InvalidateProfilesInChannelCacheByUser(userId stri
 			return nil
 		}
 
-		toPass := make([]any, 0, len(keys))
-		for i := 0; i < len(keys); i++ {
-			var userMap model.UserMap
-			toPass = append(toPass, &userMap)
-		}
+		toPass := allocateCacheTargets[model.UserMap](len(keys))
 		errs := s.rootStore.doMultiReadCache(s.rootStore.profilesInChannelCache, keys, toPass)
 		for i, err := range errs {
 			if err != nil {
@@ -177,11 +173,7 @@ func (s *LocalCacheUserStore) GetProfileByIds(ctx context.Context, userIds []str
 	remainingUserIds := make([]string, 0)
 
 	fromMaster := false
-	toPass := make([]any, 0, len(userIds))
-	for i := 0; i < len(userIds); i++ {
-		var user *model.User
-		toPass = append(toPass, &user)
-	}
+	toPass := allocateCacheTargets[*model.User](len(userIds))
 	errs := s.rootStore.doMultiReadCache(s.rootStore.userProfileByIdsCache, userIds, toPass)
 	for i, err := range errs {
 		if err != nil {
@@ -263,12 +255,7 @@ func (s *LocalCacheUserStore) GetMany(ctx context.Context, ids []string) ([]*mod
 	uniqIDs := dedup(ids)
 
 	fromMaster := false
-	toPass := make([]any, 0, len(uniqIDs))
-	for i := 0; i < len(uniqIDs); i++ {
-		var user *model.User
-		toPass = append(toPass, &user)
-	}
-
+	toPass := allocateCacheTargets[*model.User](len(uniqIDs))
 	errs := s.rootStore.doMultiReadCache(s.rootStore.userProfileByIdsCache, uniqIDs, toPass)
 	for i, err := range errs {
 		if err != nil {