std::file claims that it returns the name of a file, but it returns a relative path

[bonsairobo]

Location

https://doc.rust-lang.org/std/macro.file.html

Summary

The docs say:

Expands to the file name in which it was invoked.

But in fact, a relative path is returned. For example, if we have src/main.rs:

fn main() {
    println!("{}", std::file!())
}

This prints "src/main.rs" (on GNU/Linux).

I believe this will be a path relative to the workspace root, though an expert should confirm this.

[bjorn3]

I believe this will be a path relative to the workspace root, though an expert should confirm this.

Cargo will invoke rustc for local crates with the workspace root as working directory and for dependencies from crates.io with their source directory as working directory. For local crates it then passes a relative path as filename and for crates.io dependencies the absolute path as filename to rustc. file!() is relative based on the original filename that was passed to rustc.

[bonsairobo]

file!() is relative based on the original filename that was passed to rustc.

I'm not sure I understand this part. Could you give an example?

[bjorn3]

If you pass src/lib.rs to rustc as filename and you have a module foo at src/foo.rs, then file!() will return src/foo.rs when invoked inside that module. If you pass /path/to/lib.rs then it will return /path/to/foo.rs when invoked inside the foo module.

[bonsairobo]

Is there any way to test the crates.io behavior without first publishing the crate?

EDIT: To clarify, it would be nice to test behavior that relies on file!() in the case where your crate is being used as a crates.io dependency. Ideally the test would not involve manually invoking rustc.

(Sorry if this is a little off topic)

[bonsairobo]

And can I assume that the path would depend on the operating system? E.g. on Windows you would get an absolute path as C:\\path\to\crate\src\lib.rs?

[bjorn3]

Is there any way to test the crates.io behavior without first publishing the crate?

Yes, same behavior applies to git dependencies AFAIK, so you could create a git repo somewhere and depend on it.

And can I assume that the path would depend on the operating system? E.g. on Windows you would get an absolute path as C:\path\to\crate\src\lib.rs?

Yes

[Dylan-DPC]

Closing this as it's not an issue and it works as intended

[bonsairobo]

@Dylan-DPC Can you tell me why it's "not an issue and working as intended"? I find the documentation to be both factually incorrect and lacking a thorough explanation of how the macro actually behaves.