[BUG] importing .mojopkg runs its main() instead of only importing

[toiletsandpaper]

Bug description

When importing and calling something from .mojopkg - mojo runs only package's main, and not real main.

Steps to reproduce

I've written a minimal repro:

.
├── birds_package.mojopkg
├── main.mojo
└── simple_package
    ├── __init__.mojo
    └── birds.mojo

Where simple_package/birds.mojo is:

struct Bird:
    var name: String

    fn __init__(inout self, name: String):
        self.name = name

    fn fly(self):
        print("The bird " + self.name + " is flying")

fn main():
    var bird = Bird(name="Package")
    bird.fly()

and main.mojo:

from birds_package.birds import Bird

fn main():
    print('before pigeon')
    var b = Bird('pigeon')
    b.fly()
    print('after pigeon')

When I'm trying to import birds_package.mojopkg in main.mojo — my output is:

The bird Package is flying

And when simple_package as folder:

before pigeon
The bird pigeon is flying
after pigeon

Mojo package was created with

mojo package simple_package -o birds_package.mojopkg

and __init__.mojo is empty file

System information

❯ mojo -v
mojo 24.1.1 (0ab415f7)
❯ modular -v
modular 0.5.2 (6b3a04fd)
❯ modular host-info
  Host Information
  ================

  Target Triple: aarch64-unknown-macosx
  CPU: apple-m1
  CPU Features: aes, complxnum, crc, dotprod, fp-armv8, fp16fml, fullfp16, jsconv, lse, neon, pauth, ras, rcpc, rdm, sha2, sha3

[River707]

Thanks for the report! Mojo doesn't really have well defined support for defining a main inside of a package. We'll add an error an a follow-up release to just prevent this for now until we work through the ramifications of it.