ASP.NET Core 2.1 gives error CS2017: Cannot specify /main if building a module or library

[pranavkm]

Original issue: https://github.com/aspnet/websdk/issues/350

Steps to reproduce:

• Install .NET Core SDK 2.1
• Create a new project with dotnet new "asp.net core web app"
• The project compiles OK
• Add element <StartupObject>foo.Program</StartupObject> to the csproj

Build fails with:

1>CSC : error CS2017: Cannot specify /main if building a module or library

This error did not occur with 2.0. Also a plain .NET core console app initialized with dotnet new "console application" does not have this problem.

[pranavkm]

cc @richard-browne @vijayrkn

Likely an issue here: https://github.com/aspnet/Razor/blob/dev/src/Microsoft.NET.Sdk.Razor/build/netstandard2.0/Microsoft.NET.Sdk.Razor.Compilation.targets#L136

MainEntryPoint shouldn't apply to the Razor assembly since TargetType is set to https://github.com/aspnet/Razor/blob/dev/src/Microsoft.NET.Sdk.Razor/build/netstandard2.0/Microsoft.NET.Sdk.Razor.Compilation.targets#L159.

[JohnGalt1717]

So how do you fix it? Just remove the startup object?

[pranavkm]

Removing the startup object would be the easiest workaround. Alternatively, you could try resetting the property right before Razor compilation occurs:

<Target Name="FixStartupObjectIssue" BeforeTargets="RazorCoreCompile">
  <PropertyGroup>
    <StartupObject />
  </PropertyGroup>
</Target>

Yet another option would be to edit the actual Sdk target to not pass the property in Razor's call to the Csc task. I wouldn't recommend this fix though, since it's tied to your machine.

[mkArtakMSFT]

@pranavkm, do you have a PR ready for this?

[pranavkm]

Not as yet.