System.InvalidOperationException : A resolver is already set for the assembly.

@AArnott

After updating Nerdbank.GitVersioning to libgit2sharp 0.27.0-preview-0096, a great many of my tests are failing with this exception. Is it expected that SetConfigSearchPaths become callable-once-only?

Test Name:	GitContextLibGit2Tests.InitialDefaultState
Test FullName:	NerdBank.GitVersioning.Tests (net5.0).GitContextLibGit2Tests.GitContextLibGit2Tests.InitialDefaultState
Test Source:	D:\git\Nerdbank.GitVersioning\src\NerdBank.GitVersioning.Tests\GitContextTests.cs : line 40
Test Outcome:	Failed
Test Duration:	0:00:00

Test Name:	GitContextLibGit2Tests.InitialDefaultState
Test Outcome:	Failed
Result StackTrace:	
at LibGit2Sharp.Core.NativeMethods.git_repository_init_ext(git_repository*& repository, FilePath path, GitRepositoryInitOptions options)
   at LibGit2Sharp.Core.Proxy.git_repository_init_ext(FilePath workdirPath, FilePath gitdirPath, Boolean isBare)
   at LibGit2Sharp.Repository.Init(String path, Boolean isBare)
   at LibGit2Sharp.Repository.Init(String path)
   at RepoTestBase.InitializeSourceControl(String repoPath, Boolean withInitialCommit) in D:\git\Nerdbank.GitVersioning\src\NerdBank.GitVersioning.Tests\RepoTestBase.cs:line 108
   at RepoTestBase.InitializeSourceControl(Boolean withInitialCommit) in D:\git\Nerdbank.GitVersioning\src\NerdBank.GitVersioning.Tests\RepoTestBase.cs:line 102
   at GitContextTests..ctor(ITestOutputHelper logger) in D:\git\Nerdbank.GitVersioning\src\NerdBank.GitVersioning.Tests\GitContextTests.cs:line 35
   at GitContextLibGit2Tests..ctor(ITestOutputHelper logger) in D:\git\Nerdbank.GitVersioning\src\NerdBank.GitVersioning.Tests\GitContextTests.cs:line 23
----- Inner Stack Trace -----
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor, Boolean wrapExceptions)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
   at LibGit2Sharp.Core.NativeMethods.TryUseNativeLibrary()
   at LibGit2Sharp.Core.NativeMethods..cctor()
----- Inner Stack Trace -----
   at System.Runtime.InteropServices.NativeLibrary.SetDllImportResolver(Assembly assembly, DllImportResolver resolver)
Result Message:	
System.TypeInitializationException : The type initializer for 'LibGit2Sharp.Core.NativeMethods' threw an exception.
---- System.Reflection.TargetInvocationException : Exception has been thrown by the target of an invocation.
-------- System.InvalidOperationException : A resolver is already set for the assembly.

Originally posted by @AArnott in #1618 (comment)

Where is this SetDllImportResolver method? And why is it called twice when it's called by a static constructor?

Ok, the callstack for the original exception is:

 	System.Private.CoreLib.dll!System.ThrowHelper.ThrowArgumentException(System.ExceptionResource resource) Line 200	C#
 	System.Private.CoreLib.dll!System.Runtime.CompilerServices.ConditionalWeakTable<System.__Canon, System.__Canon>.Add(System.__Canon key, System.__Canon value) Line 85	C#
 	System.Private.CoreLib.dll!System.Runtime.InteropServices.NativeLibrary.SetDllImportResolver(System.Reflection.Assembly assembly, System.Runtime.InteropServices.DllImportResolver resolver) Line 225	C#
 	[Native to Managed Transition]	
 	[Managed to Native Transition]	
>	LibGit2Sharp.dll!LibGit2Sharp.Core.NativeMethods.TryUseNativeLibrary() Line 127	C#
 	LibGit2Sharp.dll!LibGit2Sharp.Core.NativeMethods.NativeMethods() Line 37	C#
 	[Native to Managed Transition]	
 	[Managed to Native Transition]	
 	LibGit2Sharp.dll!LibGit2Sharp.Core.Proxy.git_repository_init_ext(LibGit2Sharp.Core.FilePath workdirPath, LibGit2Sharp.Core.FilePath gitdirPath, bool isBare) Line 2487	C#
 	LibGit2Sharp.dll!LibGit2Sharp.Repository.Init(string path, bool isBare) Line 498	C#
 	LibGit2Sharp.dll!LibGit2Sharp.Repository.Init(string path) Line 485	C#
 	NerdBank.GitVersioning.Tests.dll!RepoTestBase.InitializeSourceControl(string repoPath, bool withInitialCommit) Line 108	C#

The LibGit2Sharp part of this stack includes:

libgit2sharp/LibGit2Sharp/Core/NativeMethods.cs

Lines 123 to 125 in 3d72762

    
           // NativeMethods.SetDllImportResolver(typeof(NativeMethods).Assembly, ResolveDll); 
        
           object resolveDelegate = typeof(NativeMethods).GetMethod(nameof(ResolveDll), BindingFlags.NonPublic | BindingFlags.Static).CreateDelegate(dllImportResolverType); 
        
           setDllImportResolver.Invoke(null, new object[] { typeof(NativeMethods).Assembly, resolveDelegate });

This stack includes a static constructor, so the guarantee should be that it only runs once. But maybe other code calls this NativeLibrary.SetDllImportResolver as well before the static constructor runs.

Also of note, this problem only manifests on .NET Core (3.1 or 5.0).

Ah yes, my own unit tests were calling that same NativeLibrary.SetDllImportResolver method. I suppose it was from before libgit2sharp did it on its own? Anyway, once I remove my code that calls it, the tests pass even with the libgit2sharp upgrade. 🥳

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System.InvalidOperationException : A resolver is already set for the assembly. #1855

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	// NativeMethods.SetDllImportResolver(typeof(NativeMethods).Assembly, ResolveDll);
	object resolveDelegate = typeof(NativeMethods).GetMethod(nameof(ResolveDll), BindingFlags.NonPublic \| BindingFlags.Static).CreateDelegate(dllImportResolverType);
	setDllImportResolver.Invoke(null, new object[] { typeof(NativeMethods).Assembly, resolveDelegate });

System.InvalidOperationException : A resolver is already set for the assembly. #1855

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AArnott commented on Nov 24, 2020

AArnott commented on Nov 24, 2020

AArnott commented on Nov 24, 2020

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