rustc injects main in all outputs when specifying “bin” crate type

[jethrogb]

See source code for a.rs & b.rs at the end of this issue.

expected behavior

I'd expect this:

$ rustc --crate-type=bin a.rs
$ rustc --crate-type=rlib a.rs

to generate the same output as:

$ rustc --crate-type=bin,rlib a.rs

actual behavior

But it does not:

$ rustc --crate-type=rlib a.rs
$ rustc b.rs --extern a=liba.rlib

is all peachy, versus:

$ rustc --crate-type=bin,rlib a.rs
$ rustc b.rs --extern a=liba.rlib
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" ...
  = note: /tmp/rlibtest/liba.rlib(a.0.o): In function `main':
a.cgu-0.rs:(.text.main+0x0): multiple definition of `main'
b.0.o:b.cgu-0.rs:(.text.main+0x0): first defined here
collect2: error: ld returned 1 exit status


error: aborting due to previous error

source files

// a.rs
pub fn a_fn() {
	panic!("a_fn")
}

fn main() {
	a_fn()
}

// b.rs
extern crate a;

fn main() {
	a::a_fn()
}

[Mark-Simulacrum]

Closing in favor of #22183.