`lazy_static` makes a call to some function twice

[asmmo]

I have a big project Where I use lazy_static to create a singleton. I think there is a bug in lazy_static crate (which appears in big projects only) or I am doing something wrong because the initialization function which must be called once to create the singleton is called twice.

The structure of the project is as follows

---

Foo
|__foo-core
|  |__src
|  |  |__lib.rs
|  |__Cargo.toml
|
|__foo-high
|  |__src
|  |  |__lib.rs
|  |__Cargo.toml
|
|__src
|  |__lib.rs
|__Cargo.toml

---

Foo/foo-core/src/lib.rs

pub mod my_file {
    pub struct MyFile {
        file: std::fs::File,
    }

    impl MyFile {
        pub fn open(
            path: &'static str,
        ) -> Result<MyFile, Box<dyn std::error::Error + Send + Sync>> {
            let file_ = std::fs::File::create(path)?;
            Ok(MyFile { file: file_ })
        }
    }
}

Foo/foo-high/src/lib.rs

mod high {
    mod high_child {
        #[cfg(test)]
        mod high_child_unit_tests {
            use crate::high::my_file::*;

            #[test]
            fn some_fun_test_runner() {
                MyFile::get();
                auto_fun();
                MyFile::get();
            }

            fn auto_fun() {
                // super::super::layer ::some_fun().await;
                foo::high::some_fun();
            }
        }
    }

    pub mod layer {
        use crate::high::my_file::*;

        pub fn some_fun() {
            MyFile::get();
        }
    }

    mod my_file {
        pub use foo_core::my_file as core_my_file;
        use std::sync::{Mutex, MutexGuard};
        lazy_static::lazy_static! {static ref INSTANCE: Mutex<core_my_file::MyFile> = init_fun();}

        fn init_fun() -> Mutex<core_my_file::MyFile> {
            println!("INIT");
            let location = "location.txt";
            Mutex::new(core_my_file::MyFile::open(location).expect("\nSome Error has occurred."))
        }

        pub struct MyFile {}

        impl MyFile {
            pub fn get() -> MutexGuard<'static, core_my_file::MyFile> {
                println!("GET");
                INSTANCE.lock().expect("The mutex has been poisoned")
            }
        }
    }
}

pub mod layer {
    pub use crate::high::layer::*;
}

Foo/foo-core/Cargo.toml

[package]
name = "foo-core"
version = "0.1.0"
edition = "2018"

Foo/foo-high/Cargo.toml

[package]
name = "foo-high"
version = "0.1.0"
edition = "2018"

[dependencies]
foo-core = { version = "0.1.0", path = "../foo-core" }
lazy_static = "1.4.0"

[dev-dependencies]
foo = { version = "0.1.0", path = "../" }

Foo/Cargo.toml

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

[dependencies]
foo-high = { version = "0.1.0", path = "foo-high" }

[workspace]
members = ["foo-high", "foo-core"]

When I ran the some_fun_test_runner test with -- --no-capture, I see 3 GETs and 2 INITs while INIT must print only once.
When I changed the architecture, the function was called once but I need this architecture.
And when I changed foo::high::some_fun(); (in auto_fun) to super::super::layer::some_fun();, the function was called once too.
I can't understand this behavior. I used once_cell too but I have got the same results

[mbrubeck]

In this code, you are calling a function from the top-level foo crate, but I can't see where this function is defined because you did not list the text of Foo/src/lib.rs:

fn auto_fun() {
    // super::super::layer ::some_fun().await;
    foo::high::some_fun();
}

I suspect that foo::high contains a second copy of the code from foo-high, and so it is initializing a second lazy_static variable, which is why you see two INIT lines.

For example, if you did something like this, then all the code from foo-high/src/lib.rs would be compiled twice:

#[path = "foo-high/src/lib.rs"]
mod high;

If I change auto_fun to call the function defined in foo-high, then the test correctly prints INIT only once:

fn auto_fun() {
    crate::high::layer::some_fun();
}