What does compilationOptions.emitEntryPoint mean?

Question

Just installed the rc1 tools and created a new web project to see what has changed in the template.

I noticed that project.json now contains:

"compilationOptions": {
    "emitEntryPoint": true
}

But it's unclear what this does.

Does anyone have an idea?

Answer 1

As mentioned below: It looks like it is a flag to the compiler to indicate that the project is a console application vs. a library (namely: a console application must contain public static void Main())

You can see from the source here.

In the new RC1 default web application template, you'll notice at the bottom of Startup.cs there is a new expression bodied method that acts as the entry point:

public static void Main(string[] args) => WebApplication.Run<Startup>(args);

If you remove this method then perform a build (dnu build) you will get an error:

error CS5001: Program does not contain a static 'Main' method suitable for an entry point

However, if you change the emitEntryPoint flag to false and attempt to build again, it will succeed. This is because it is creating a library instead of a console app.

Answer 2

I see this in the source;

var outputKind = compilerOptions.EmitEntryPoint.GetValueOrDefault() ?
    OutputKind.ConsoleApplication : OutputKind.DynamicallyLinkedLibrary;

Looks like it tells the compiler whether to create a Console Application or a Library.

Additionaly, if you create a new Class Library (Package) and Console Application (Package) in VS2015 you'll see that project.json for the Console Application includes the following, while the Class Library does not;

"compilationOptions": {
  "emitEntryPoint": true
}