Nested `main` causes build error

[joshlf]

The following code snippets seem to cause the playground to interpret the file as a binary (including changing the "build" button to say "run"), but then rustc can't find a crate-level main function, and so fails compilation:

mod foo {
    fn main() {}
}

fn foo() {
    fn main() {}
}

IMO, only main functions at the crate level should cause this behavior.

[shepmaster]

Yep!

The automatic selection is done via simple regexes.

If you’d like to fix this, you are welcome to explore an alternate regex or parsing mechanism to make the decision.

In the meantime, you can always override the automatically-selected mode:

[joshlf]

Ah, seems like a much more involved fix. Maybe eventually we'll want to wasm-ify the Rust parser, but I think for the time being this is probably a small enough wart that it can be ignored. Thanks for the quick reply!

[shepmaster]

wasm-ify the Rust parser

It’s possible (see #357), but one important thing to continue to preserve is the ability to handle malformed Rust code.