Could not find a part of the path ... bin\roslyn\csc.exe

The problem with the default VS2015 templates is that the compiler isn't actually copied to the tfr\bin\roslyn\ directory, but rather the {outdir}\roslyn\ directory

Add this code in your .csproj file:

<Target Name="CopyRoslynFiles" AfterTargets="AfterBuild" Condition="!$(Disable_CopyWebApplication) And '$(OutDir)' != '$(OutputPath)'">
    <ItemGroup>
      <RoslynFiles Include="$(CscToolPath)\*" />
    </ItemGroup>
    <MakeDir Directories="$(WebProjectOutputDir)\bin\roslyn" />
    <Copy SourceFiles="@(RoslynFiles)" DestinationFolder="$(WebProjectOutputDir)\bin\roslyn" SkipUnchangedFiles="true" Retries="$(CopyRetryCount)" RetryDelayMilliseconds="$(CopyRetryDelayMilliseconds)" />
</Target>

A clean and rebuild worked for me!

TL; DR

run this in the Package Manager Console:

Update-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform -r

More information

This problem is not related to Visual Studio itself, so answers suggesting adding build steps to copy files over are rather a workaround. Same with adding compiler binaries manually to the project.

The Roslyn compiler comes from a NuGet package and there is/was a bug in some versions of that package (I don't know exactly which ones). The solution is to reinstall/upgrade that package to a bug-free version. Originally before I wrote the answer back in 2015 I fixed it by installing following packages at specific versions:

• Microsoft.Net.Compilers 1.1.1
• Microsoft.CodeDom.Providers.DotNetCompilerPlatform 1.0.1

Then I looked into .csproj and made sure that the paths to packages are correct (in my case ..\..\packages\*.*) inside tags <ImportProject> on top and in <Target> with name "EnsureNuGetPackageBuildImports" on the bottom. This is on MVC 5 and .NET Framework 4.5.2.