Summary

Allow a re-export of a function as entry point main.

Motivation

Functions and re-exports of functions usually behave the same way, but they do not for the program entry point main. This RFC aims to fix this inconsistency.

The above mentioned inconsistency means that e.g. you currently cannot use a library’s exported function as your main function.

Example:

pub mod foo {
    pub fn bar() {
        println!("Hello world!");
    }
}
use foo::bar as main;

Example 2:

extern crate main_functions;
pub use main_functions::rmdir as main;

See also https://github.com/rust-lang/rust/issues/27640 for the corresponding issue discussion.

The #[main] attribute can also be used to change the entry point of the generated binary. This is largely irrelevant for this RFC as this RFC tries to fix an inconsistency with re-exports and directly defined functions. Nevertheless, it can be pointed out that the #[main] attribute does not cover all the above-mentioned use cases.

Detailed design

Use the symbol main at the top-level of a crate that is compiled as a program (--crate-type=bin) – instead of explicitly only accepting directly-defined functions, also allow (possibly non-pub) re-exports.

Drawbacks

None.

Alternatives

None.

Unresolved questions

None.