MM-37721: Add prop for post preview before saving record. (#18361)

* MM-37721: Add prop for post preview before saving record.

* MM-37721: Test fix.

* MM-37721: Adds test.

* MM-37721: Fixes vet.

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

app/post.go

@@ -297,6 +297,12 @@ func (a *App) CreatePost(c *request.Context, post *model.Post, channel *model.Ch
 		}
 	}
 
+	post = a.PreparePostForClient(post, true, false)
+	previewPost := post.GetPreviewPost()
+	if previewPost != nil {
+		post.AddProp(model.PostPropsPreviewedPost, previewPost.PostID)
+	}
+
 	rpost, nErr := a.Srv().Store.Post().Save(post)
 	if nErr != nil {
 		var appErr *model.AppError
@@ -345,11 +351,6 @@ func (a *App) CreatePost(c *request.Context, post *model.Post, channel *model.Ch
 	// to be done when we send the post over the websocket in handlePostEvents
 	rpost = a.PreparePostForClient(rpost, true, false)
 
-	rpost, nErr = a.addPostPreviewProp(rpost)
-	if nErr != nil {
-		return nil, model.NewAppError("CreatePost", "app.post.save.app_error", nil, nErr.Error(), http.StatusInternalServerError)
-	}
-
 	// Make sure poster is following the thread
 	if *a.Config().ServiceSettings.ThreadAutoFollow && rpost.RootId != "" {
 		_, err := a.Srv().Store.Thread().MaintainMembership(user.Id, rpost.RootId, store.ThreadMembershipOpts{