Version height calculated differently in 3.4 with new git backend

[nmeyering]

It seems git version height still yields different results with the new git backend in some cases. This tripped us up because it meant old packages were being overwritten with new ones, causing chaos in our dependency graph.

Seems to be different from #587 since we get a non-zero version and it still happens in 3.4.231?

$ dotnet tool install --global nbgv
You can invoke the tool using the following command: nbgv
Tool 'nbgv' (version '3.4.231') was successfully installed.
$ nbgv.exe get-version
Version:                      1.0.28.5486
AssemblyVersion:              1.0.0.0
AssemblyInformationalVersion: 1.0.28+6e152011
NuGetPackageVersion:          1.0.28
NpmPackageVersion:            1.0.28

and with the old git backend:

$ NBGV_GitEngine=LibGit2 nbgv.exe get-version
Version:                      1.0.49.5486
AssemblyVersion:              1.0.0.0
AssemblyInformationalVersion: 1.0.49+6e152011
NuGetPackageVersion:          1.0.49
NpmPackageVersion:            1.0.49

Nbgv version 3.3.37 yields 1.0.49 also.

The version.json file is:

{
  "$schema": "https://raw.githubusercontent.com/dotnet/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
  "version": "1.0",
  "pathFilters": ["."],
  "gitCommitIdShortFixedLength": 8,
  "publicReleaseRefSpec": [
    "^refs/heads/develop$"
  ]
}

[AArnott]

Ooh, that doesn't sound good. Sorry about the package version overwriting. That sounds terrible.

Can you share your git history / repo so we can use it to study the problem?
What level in your repo is your version.json file found in? Can you tell me about its history, including how long path filters have been in there? Do other version.json files exist in your repo or in the past?

[nmeyering]

Hey thanks for the quick reply.

Sorry, I can't share the repo itself, but I'll try to give as much context as possible.
The version.json file is two levels deep at the root of its dotnet project (next to the .csproj file): Repository/src/Project/version.json while Repository/.git is the git dir location.
The version.json only has one commit in its history and it's the same commit that also introduced the whole src/Project dir. So therefore the same path filter has always been there.

[AArnott]

Thank you. Do you think you could try creating a new repo with a similar path and history structure (no need for 1000s of commits -- just enough to represent the history of the version.json file and perhaps a dummy file in the project dir) to see if you can repro it on a repo you can share?

[nmeyering]

Ok I took the time and thankfully it was fairly easy to reproduce. All you apparently need is a merge commit with relevant changes in both parents.

If you clone this repo: https://github.com/nmeyering/nbgv-bug-repro

and run

$ nbgv get-version -v VersionHeight; NBGV_GitEngine=LibGit2 nbgv get-version -v VersionHeight
2
3

you should see the output differs.

[AArnott]

I have written a unit test to repro the issue using your shared repro as a template. Thank you. I'm investigating a fix.