How to Use NuGet on Mono, Part IV

[Update: Microsoft starts to officially support Mono, so please simply use latest NuGet executable such as 3.5]

In part I and part II I have already mentioned the steps you need to follow. Part III is about Mono packaging. This post described how we should patch NuGet so that it works better on Mono.

I have opened a bug of NuGet on its homepage earlier today. I noticed it when I attempted to build my open source project #SNMP on Mono/Linux, as NuGet seems to ignore installed packages, which leads to multiple downloads of the same package and hurt performance significantly.

Therefore, I downloaded NuGet source code on Mono/Linux and planed to build it. Failed. Alright, this is not a NuGet issue right now, as xbuild is not strong enough to support the build, which have been reported a long time ago and multiple times. Sadly Mono guys do not yet resolve it.

Anyway, I then downloaded the source code (NuGet 2.2 release, not master) to Windows, and used Visual Studio 2012 to build it. After that, I copied the instrumented binary (with Console.WriteLine everywhere necessary) to my Linux box. Guess what? This triggers a very strange error message, which I could not find any information on the web,

Mono: gc took 15 usecs
Mono: Assembly Loader probing location: '/usr/lib/mono/4.0/mscorlib.dll'.
Mono: Image addref mscorlib[0x9960ab0] -> /usr/lib/mono/4.0/mscorlib.dll[0x99601b8]: 2
Mono: AOT failed to load AOT module /usr/lib/mono/4.0/mscorlib.dll.so: /usr/lib/mono/4.0/mscorlib.dll.so: cannot open shared object file: No such file or directory

Mono: Assembly Loader loaded assembly from location: '/usr/lib/mono/4.0/mscorlib.dll'.
Mono: Config attempting to parse: '/usr/lib/mono/4.0/mscorlib.dll.config'.
Mono: Config attempting to parse: '/etc/mono/assemblies/mscorlib/mscorlib.config'.
Mono: Assembly mscorlib[0x9960ab0] added to domain NuGet.exe, ref_count=1
Mono: Config attempting to parse: '/etc/mono/config'.
Mono: Config attempting to parse: '/home/lextm/.mono/config'.
Mono: Assembly Loader probing location: 'NuGet.exe'.
Mono: Image addref NuGet[0x99adcf8] -> /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe[0x99ad030]: 2
Mono: Assembly NuGet[0x99adcf8] added to domain NuGet.exe, ref_count=1
Mono: AOT failed to load AOT module /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe.so: /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe.so: cannot open shared object file: No such file or directory

Mono: Assembly Loader loaded assembly from location: 'NuGet.exe'.
Mono: Config attempting to parse: '/home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe.config'.
Mono: Config attempting to parse: '/etc/mono/assemblies/NuGet/NuGet.config'.
Mono: Assembly Loader probing location: 'NuGet.exe'.
Mono: AOT failed to load AOT module /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe.so: /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe.so: cannot open shared object file: No such file or directory

Mono: Assembly Ref addref NuGet[0x99adcf8] -> mscorlib[0x9960ab0]: 2
Mono: Assembly Loader probing location: '/home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll'.
Mono: Image addref NuGet.Core[0x99b5038] -> /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll[0x99b4708]: 2
Mono: Assembly NuGet.Core[0x99b5038] added to domain NuGet.exe, ref_count=1
Mono: AOT failed to load AOT module /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll.so: /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll.so: cannot open shared object file: No such file or directory

Mono: Assembly Loader loaded assembly from location: '/home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll'.
Mono: Config attempting to parse: '/home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.Core.dll.config'.
Mono: Config attempting to parse: '/etc/mono/assemblies/NuGet.Core/NuGet.Core.config'.
Mono: Assembly Ref addref NuGet[0x99adcf8] -> NuGet.Core[0x99b5038]: 2
Mono: Assembly Ref addref NuGet.Core[0x99b5038] -> mscorlib[0x9960ab0]: 3
Missing method .ctor in assembly /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe, type System.Runtime.CompilerServices.ExtensionAttribute
Mono: The class System.Runtime.CompilerServices.ExtensionAttribute could not be loaded, used in NuGet
Can't find custom attr constructor image: /home/lextm/Downloads/ConsoleApplication3/.nuget/NuGet.exe mtoken: 0x0a000018

If you happen to meet the same exception message after following http://docs.nuget.org/docs/contribute/setting-up-the-nuget-development-environment, please don’t panic as this is by design. The NuGet site steps will generate binaries compiled against .NET 4.5 profile, which is not yet available in Mono stable releases (2.10.*). You have to use Visual Studio 2010 to build the binaries (Core and CommandLine projects). [Update: the exception is not Mono alone. If you run a .NET 4.5 program on .NET 4 you might hit the same, http://www.mattwrock.com/post/2012/02/29/What-you-should-know-about-running-ILMerge-on-Net-45-Beta-assemblies-targeting-Net-40.aspx]

Well, if you find that you cannot open the two projects correctly in VS2010, please go to Build\NuGet.Settings.targets file, and change

$(MSBuildExtensionsPath)\..\Microsoft Visual Studio 11.0\Common7\IDE

to something invalid, such as

$(MSBuildExtensionsPath)\..\Microsoft Visual Studio 12.0\Common7\IDE

Then VS2010 should be able to open the two projects correctly.

Finally the instrumented binary told me that PhysicalFileSystem.GetDirectory and PhysicalFileSystem.GetFiles do not work as expected. Why? I laughed when I opened this method,

private static string EnsureTrailingSlash(string path)
{
    if (!path.EndsWith("\\", StringComparison.Ordinal))
    {
        path += "\\";
    }
    return path;
}

OK. If you are familiar with this guide, it is obvious that \\ is the culprit. You should use Path.DirectorySeparatorChar to replace it.

Right now I am ready to fork NuGet, fix this issue, and send back a pull request.

[Update: Luckily NuGet guys already fixed it in master branch on Dec 5, 2012. Hope its 2.3 release comes soon.]

After so many struggles, I finally finish the series of this topic, and hope you also learn a lot from my experience like I did.