Temporary fix for slack attachment fields being clobbered by plugins (#9935)

app/post.go

@@ -7,6 +7,7 @@ import (
 	"crypto/hmac"
 	"crypto/sha1"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"net/http"
 	"strings"
@@ -139,6 +140,19 @@ func (a *App) CreatePost(post *model.Post, channel *model.Channel, triggerWebhoo
 		return nil, err
 	}
 
+	// Temporary fix so old plugins don't clobber new fields in SlackAttachment struct, see MM-13088
+	if attachments, ok := post.Props["attachments"].([]*model.SlackAttachment); ok {
+		jsonAttachments, err := json.Marshal(attachments)
+		if err == nil {
+			attachmentsInterface := []interface{}{}
+			err = json.Unmarshal(jsonAttachments, &attachmentsInterface)
+			post.Props["attachments"] = attachmentsInterface
+		}
+		if err != nil {
+			mlog.Error("Could not convert post attachments to map interface, err=%s" + err.Error())
+		}
+	}
+
 	if pluginsEnvironment := a.GetPluginsEnvironment(); pluginsEnvironment != nil {
 		var rejectionError *model.AppError
 		pluginContext := &plugin.Context{}