TFS getting Branch -> Rollback -> Merge backwards and wanting to erase all changes

Question

We had some changes committed (let's call it changeset1) in what we call the Dev branch of our project that really should've been done in a new branch. So what I did to fix it is create a new branch off of the Dev branch (let's call it Dev2). Then I rolled back the Dev branch to before changeset1. So now the code base looks like the development was done in Dev2 and Dev was never touched.

Later, I then did some development in Dev, merged it to Stage, and then Prod. Now I'm trying to also merge those changes into Dev2 but when I perform the merge (in VS 2017) it auto-merges everything and it wants to delete all of the changes from changeset1. I guess because I rolled back Dev after changeset1, it sees that as the latest change and wants to merge that rollback to Dev2. How can I get it to see Dev2 as the latest and merge my new Dev changes into it without deleting changeset1's changes?

For clarification, Dev is the parent of both the Stage and Dev2 branches.

Answer 1

According to your description, seems the merge process didn't pick up the rollback changeset1 in Dev branch, which cause this scenario.

This is caused you didn't use /keepmergehistory option during your rollback.

tf rollback /keepmergehistory

This option has an effect only if one or more of the changesets that you are rolling back include a branch or merge change. Specify this option if you want future merges between the same source and the same target to exclude the changes that you are rolling back.

Please go through the detail explanation and some examples in our official tutorial here: Example: /keepmergehistory Option

Besides, you could also take a look at this similar question: TFS merge doesn't pick up rollback changeset(s)

Answer 2

I figured out a way to resolve it. So to re-iterate, I think the problem was the changes I wanted were in Dev2, but I rolled back Dev after creating Dev2 so the rollback was the most recent change so the merge wanted to keep the rollback and delete the changes I wanted to keep from Dev2. So I came to the conclusion that what I need to do was somehow apply those changes to Dev2 again as if they were a new edit.

So what I did is:

1. Move the changes from changeset1 into a Shelveset
2. Merge Dev to Dev2, thereby deleting the desired changes
3. Unshelve the changeset1 Shelveset to Dev2

#1 was the hardest part. First I created two new workspaces: DevC0 and DevC1. I pulled the changeset from before changeset1 into DevC0 and pulled changeset1 into DevC1. So now DevC1 has all the changes I'm interested in and DevC0 does not. I then copied all of the changed files (using BeyondCompare but I think you could just copy all your files except for the TFS folders/files too) from DevC1 to DevC0. Then at the command line, I did a tf vc reconcile on the DevC0 folder to allow it to recognize all the changes I just copied over. E.G. (I didn't actually want /deletes in my case):

tf vc /reconcile /promote /adds /deletes /diff /recursive [DevC0 itemspec]

(Make sure your command prompt's working directory is a directory mapped to your target workspace). After that, all of the differences now appear as pending changes in Visual Studio Team Explorer/Source Control Explorer. So from there I can create a Shelveset.

#2 was just a typical merge from Dev to Dev2. It deleted all of the changes and made Dev2 match Dev. I don't know if I needed to check this in before applying the Shelveset but I did.

#3 My changeset1 changes are in my Shelveset, but the Shelveset belongs to the Dev branch. Luckily, Team Foundation Power Tools can unshelve a Shelveset to a different branch. E.G:

tfpt unshelve /migrate /source:"[Dev server path]" /target:"[Dev2 server path]"

This opened a window with merge options for each file. I manually reviewed the first few then tried auto-merging all. That did the equivalent of what merging via Visual Studio does - it auto merged where possible and left the conflicts up to me in that same window. After that, it appeared all of the desired changes were now pending changes in Dev2 and I checked them in.

I then tried a merge from Dev2 back to Dev just to see if it was going to behave correctly and it did merge all of the changes to Dev and marked many of the changes that were deleted by the original rollback as undeleted. For now, I undid pending changes from that merge until we are actually ready to merge this sub-branch of work into our main Dev branch.