LibGit2Sharp.Core.Proxy.git_commit_tree_id throws NullReferenceException in shallow clones

[AArnott]

Reproduction steps

dotnet tool install -g nbgv
git clone https://github.com/aarnott/nerdbank.streams  --depth 10
cd .\nerdbank.streams\
nbgv get-version

Expected behavior

An exception thrown explaining that data is missing because of a shallow clone.

Actual behavior

A NullReferenceException that does not suggest the underlying problem.

Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at LibGit2Sharp.Core.Proxy.git_commit_tree_id(ObjectHandle obj)
   at LibGit2Sharp.Commit.<>c__DisplayClass11_0.<.ctor>b__0(ObjectHandle obj)
   at LibGit2Sharp.Core.GitObjectLazyGroup.<>c__DisplayClass3_0`1.<Singleton>b__0()
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at Nerdbank.GitVersioning.VersionFile.GetVersion(Commit commit, String repoRelativeProjectDirectory) in D:\a\1\s\src\NerdBank.GitVersioning\VersionFile.cs:line 52
   at Nerdbank.GitVersioning.GitExtensions.CommitMatchesVersion(Commit commit, SemanticVersion expectedVersion, Position comparisonPrecision, String repoRelativeProjectDirectory) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 450
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 676
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping)   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
 in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
 in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at Nerdbank.GitVersioning.GitExtensions.GetCommitHeight(Commit commit, Dictionary`2 heights, Func`2 continueStepping) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 681
   at Nerdbank.GitVersioning.GitExtensions.GetVersionHeight(Commit commit, String repoRelativeProjectDirectory, Version baseVersion) in D:\a\1\s\src\NerdBank.GitVersioning\GitExtensions.cs:line 65
   at Nerdbank.GitVersioning.VersionOracle..ctor(String projectDirectory, Repository repo, Commit head, ICloudBuild cloudBuild, Nullable`1 overrideVersionHeightOffset, String projectPathRelativeToGitRepoRoot) in D:\a\1\s\src\NerdBank.GitVersioning\VersionOracle.cs:line 86
   at Nerdbank.GitVersioning.Tool.Program.OnGetVersionCommand(String projectPath, String format, String singleVariable, String versionOrRef) in D:\a\1\s\src\nbgv\Program.cs:line 305
   at Nerdbank.GitVersioning.Tool.Program.MainInner(String[] args) in D:\a\1\s\src\nbgv\Program.cs:line 149
   --- End of inner exception stack trace ---
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Version of LibGit2Sharp (release number or SHA1)

0.27.0-preview.7+gd47cfd9144.libgit2-572e4d8

Operating system(s) tested; .NET runtime tested

Windows 10. .NET Core

[olivier-spinelli]

In addition to the better exception you suggest, I'd love to benefit of a simple bool IsShallowed {get; } or IsInvalid or IsOutOfClone that would avoid an awful try/catch.

[vincentcastagna]

We are still experiencing this issue with git version 5.10.1 on azure devops pipeline.

The fix is to specify a max depth of 0 with a checkout task before gitversion :

steps:
- checkout: self 
  fetchDepth: 0  
  clean: true
  
- task: gitversion/setup@0
  inputs:
    versionSpec: '5.10.1'
  displayName: 'Install GitVersion'

[olivier-spinelli]

In the v0.20.0 (at least), this has been "fixed" (at least for my usage): a commit.Parents is empty when the parent commit is not reachable, so that I don't hit the NRE anymore... But previously, I could detect a shallow clone, and now I'm "blind". Is there a way to know that there is a Parent that has been "evicted"?