"Earlier code should have sorted topologically or failed" assertion was hit

[jnm2]

Got a report that this assertion was hit:

tfvc-migrator/src/TfvcMigrator/Program.cs

Line 263 in 359ac31

throw new InvalidOperationException("Should not be reachable. Earlier code should have sorted topologically or failed.");

This indicates that it was migrating a merge changeset, and that it was unable to find a previously-migrated commit corresponding to a parent changeset of the merge. The question is why it was migrating a merge changeset before migrating one of its parents.

To know why this happened is tricky without a crash dump. One possibility is a bug in TopologicalSortExtensions.cs.

[jnm2]

I have a feeling that this might be something I also hit in a particular test migration scenario, prompting me to start on main...support_branch_source_renames.

[JohanLarsson]

CS319321 (19,4 %, 1 331 ms/changeset, ETA 2,1 hours)...Unhandled exception: System.InvalidOperationException: A commit should have been created for the parent changeset 319103 before reaching this point.

[JohanLarsson]

Did more digging using the additional error info.
It goes wrong where we had a TFS branch that was merged more than once.

[jnm2]

I've seen it handle that scenario, I believe. There might be another element to it. Was the branch ever renamed? I have a branch in the works that starts reacting to source-renames.

[JohanLarsson]

I have no memory of the branch being renamed but have poor memory.

[JohanLarsson]

To expand on the above we have

1. A branch with two commits that were merged
2. Then more commits were added to the branch and it was merged again a couple of times.
3. Don't remember if there were any commits made the main branch between.