GitCommitDate is author date rather than commit date

[KalleOlaviNiemitalo]

The value of the MSBuild property $(GitCommitDateTicks) comes from the Git author date, even though the name and API documentation indicate that it should come from the Git commit date. The commit date would be more useful in our workflow in which we often cherry-pick commits that are several months old. If the commit date is old, then it is easy to know for sure that the deployed version cannot include any changes that were implemented after that date. The author date cannot be used for this purpose.

Reproduced with Nerdbank.GitVersioning 3.4.240, but the code looks like it works like that in v3.5.113 too:

Nerdbank.GitVersioning/src/NerdBank.GitVersioning/LibGit2/LibGit2Context.cs

Line 50 in a908c6d

public override DateTimeOffset? GitCommitDate => this.Commit?.Author.When;

Nerdbank.GitVersioning/src/NerdBank.GitVersioning/Managed/ManagedGitContext.cs

Line 53 in a908c6d

public override DateTimeOffset? GitCommitDate => this.Commit is { } commit ? (commit.Author?.Date ?? this.Repository.GetCommit(commit.Sha, readAuthor: true).Author?.Date) : null;

Nerdbank.GitVersioning/src/NerdBank.GitVersioning.Tests/GitContextTests.cs

Line 43 in a908c6d

Assert.Equal(this.LibGit2Repository.Head.Tip.Author.When, this.Context.GitCommitDate);

[KalleOlaviNiemitalo]

The GitCommitDateTicks property for MSBuild has used the author date ever since it was added in #329 for the feature request #328. Neither of those has any comments on author date vs. commit date.

@qmfrederik, did your scenario need specifically the author date?

[AArnott]

I'm ok with changing the code to retrieve the commit date instead. If someone needs the author date, we should add that as another property. Care to send a PR?

[KalleOlaviNiemitalo]

I don't have a Windows instance on which I could install VS2019, so won't make a pull request.