Cannot use types from class libraries (csproj) in razor views

[ShadowDancer]

Title

Cannot use types from class libraries (csproj) in razor views

Functional impact

Cannot use types from other systems in razor views (compiled code works as expected).
For example I cannot keep my cms in separate dll.

Minimal repro steps

-create new webapplication rc2 project from template
-create new class library
-create example type in class library
-add reference to class library from rc2 project
-use type from class library

https://github.com/ShadowDancer/rc2_razor_references

Expected result

Compiled view.

Actual result

The type or namespace name 'ClassLibrary' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'ExampleClass' could not be found (are you missing a using directive or an assembly reference?)

[Eilon]

@pakrym @abpiskunov @pranavkm any ideas on Razor views in a project.json project referencing types from a CSPROJ?

[juergenr]

Same problem:

• cannot reference class library
• but @using System.IO works

When I use:
string s = File.ReadAllText(@"C:\Test\test.txt");
I cannot view s in Debug mode!

[pranavkm]

@ShadowDancer I can't restore your project:

Errors in \rc2_razor_references\src\rc2test\project.json
    Unable to resolve 'ClassLibrary' for '.NETFramework,Version=v4.5.1'.

Are you missing something from it?

[ShadowDancer]

@pranavkm
I can't restore it either with dotnet cli, however project is compiled successfully by VisualStudio, and all types are available in rc2test project - generally it works until you attempt to render razor view with type from ClassLibrary.

For instance in my project (I mean business project, not rc2_razor_references) I have whole Startup.cs class moved to class library and webapp is bootstrapped correctly. To demonstrate it I added new commit, so rc2_razor_references now prints string generated by type in ClassLibrary to debug output when constructor of Startup is called (you need to open it in visual studio and start rc2test project), however that class is not available when razor tries to compile it into view.

I guess that It has something to do with moving away from dnx or new "preserveCompilationContext" option? Wrap projects are not used anymore, so I just referenced cspoj libraries from xproj and application is compiled (but not razor).

[patrikwlund]

I don't know if this has any effect on this, but project.fragment.lock.json puts the location of ClassLibrary.dll here:
bin/Debug/ClassLibrary.dll

instead of here (where it's actually located):
bin/Debug/net451/win7-x64/ClassLibrary.dll

[ShadowDancer]

@patrikwlund
Looks like that paths in *.lock.json files are relative to project or package root, so
bin/Debug/ClassLibrary.dll
is relative to csproj directory
/ClassLibrary
directory, and dll file is there.

[abpiskunov]

@patrikwlund could you please specify what was your xproj and csproj project types and their target frameworks? i need to know that to see what is going on with paths specified in fragment.lock file.

[abpiskunov]

Also, here is related issue aspnet/Mvc#4686 . See my reply there.

[patrikwlund]

@abpiskunov I cloned ShadowDancer's solution, so:
Rc2 web application + csproj class library
Both for net451

[ShadowDancer]

@abpiskunov
Correct me If I am wrong, but if dll is missing (for instance if I manually delete ClassLibrary.dll from my output folder) exception is thrown when I attempt to execute code from that deleted assembly.

In provided example I can execute that code, so dll is loaded. Somehow Razor compiler cannot use that assembly though.

[abpiskunov]

About dll path, with your projects and target frameworks, it seems that fragment json has correct path to ClassLibrary.dll located under csproj path. The path bin/Debug/net451/win7-x64/ClassLibrary.dll that you specified is where it was copied under web app's.

If that is true, it means that for your case of net451 - dlls are copied (the active issue in RC2 was about netstandard target framework). and yes, problem is that dll indeed is not used/found correctly by compiler at runtime.

[abpiskunov]

Please confirm that dll is copied under web app's bin folder. Btw, you can refernce code in VS and intellisense works for you, because in VS references are resolved via project references not just dlls as it happens at runtime, thats why it works in VS.

[ShadowDancer]

Yes it is, as pointed out by partrikwlund:
bin/Debug/net451/win7-x64/ClassLibrary.dll

Here is entire bin folder if you want to take look (rc2test is AspNetCore webapp and ClassLibrary.dll is csproj):
http://pastebin.com/3z0vrAfC

Btw, you can refernce code in VS and intellisense works for you, because in VS references are resolved via project references not just dlls as it happens at runtime, thats why it works in VS

To make it clear - it works at runtime for code compiled from .cs files. I can use class from dll in AspNetCore executable - it compiles and executes without problem.
It doesn't work for code generated by razor at runtime from .cshtml with types from referenced .csproj assembly. Compiler throws when attempting to compile.

[pranavkm]

@ShadowDancer - Razor compilation in Mvc uses the deps file that is produced by the compiler when you set preserveCompilationContext to determine what assemblies to use for runtime compilation. It seems that the deps file is missing bits of useful information for Razor compilation to discover csproj based class library references \ binaries. For RC2, you should be able to work around this by explicitly adding references to Razor compilation using RazorViewEngineOptions.CompilationCallback. See aspnet/Mvc#4087 (comment)

[patrikwlund]

@pranavkm @ShadowDancer I can confirm that setting RazorViewEngineOptions.CompilationCallback does the job as a workaround. The razor view compiles successully.

var myAssemblies = AppDomain.CurrentDomain.GetAssemblies().Select(x => MetadataReference.CreateFromFile(x.Location)).ToList();

services.Configure((RazorViewEngineOptions options) =>
{
    var previous = options.CompilationCallback;
    options.CompilationCallback = (context) =>
    {
        previous?.Invoke(context);

        context.Compilation = context.Compilation.AddReferences(myAssemblies);
    };
});