Building a project assumes library crate type

Let's consider this example

fn foo() {
    println!("foo");
}

fn main() {
    foo();
}

Normally the playground suggests you to "run" the project. If you just want to check it without actually running it, you can use the "build" command in the burger menu next to "run".
But then the playground/compiler assumes that the crate type is a library and annotates the dead code (not exported, therefore dead).

I would suggest to investigate if there is a function main and change the crate type accordingly.

Start with the playground's burger-menu build command and trace how it selects the crate type before invoking the compiler. Check the behavior with the provided example containing main; done means build selects the appropriate crate type and no longer reports foo as dead code solely because it is not exported.