PLT-6960 Only update post.EditAt when the message changes (#6840)

app/post.go

@@ -266,9 +266,11 @@ func UpdatePost(post *model.Post, safeUpdate bool) (*model.Post, *model.AppError
 	newPost := &model.Post{}
 	*newPost = *oldPost
 
+	if newPost.Message != post.Message {
 		newPost.Message = post.Message
 		newPost.EditAt = model.GetMillis()
 		newPost.Hashtags, _ = model.ParseHashtags(post.Message)
+	}
 
 	if !safeUpdate {
 		newPost.IsPinned = post.IsPinned

app/post_test.go

@@ -5,11 +5,37 @@ package app
 
 import (
 	"testing"
+	"time"
 
-	"github.com/mattermost/platform/model"
 	"fmt"
+	"github.com/mattermost/platform/model"
 )
 
+func TestUpdatePostEditAt(t *testing.T) {
+	th := Setup().InitBasic()
+
+	post := &model.Post{}
+	*post = *th.BasicPost
+
+	post.IsPinned = true
+	if saved, err := UpdatePost(post, true); err != nil {
+		t.Fatal(err)
+	} else if saved.EditAt != post.EditAt {
+		t.Fatal("shouldn't have updated post.EditAt when pinning post")
+
+		*post = *saved
+	}
+
+	time.Sleep(time.Millisecond * 100)
+
+	post.Message = model.NewId()
+	if saved, err := UpdatePost(post, true); err != nil {
+		t.Fatal(err)
+	} else if saved.EditAt == post.EditAt {
+		t.Fatal("should have updated post.EditAt when updating post message")
+	}
+}
+
 func TestPostReplyToPostWhereRootPosterLeftChannel(t *testing.T) {
 	// This test ensures that when replying to a root post made by a user who has since left the channel, the reply
 	// post completes successfully. This is a regression test for PLT-6523.