How to use a local unpublished crate?

Question

I've made a library:

cargo new my_lib

and I want to use that library in a different program:

cargo new my_program --bin

extern crate my_lib;

fn main {
    println!("Hello, World!");
}

what do I need to do to get this to work?

They aren't in the same project folder.

.
├── my_lib
└── my_program

Hopefully this makes sense.

I thought I'd be able to override the path as per the Cargo guide , but it states

You cannot use this feature to tell Cargo how to find local unpublished crates.

This is when using the latest stable version of Rust (1.3).

Answer 1

Add a dependency section to your executable's Cargo.toml and specify the path:

[dependencies.my_lib]
path = "../my_lib"

or the equivalent alternate TOML:

[dependencies]
my_lib = { path = "../my_lib" }

Check out the Cargo docs for specifying dependencies for more detail, like how to use a git repository instead of a local path.

Answer 2

I was looking for an equivalent to mvn install . While this question is not quite a duplicate of my original question, anyone who stumbles across my original question and follows the link here will find a more complete answer.

The answer is "there is no equivalent to mvn install because you have to hard-code the path in the Cargo.toml file which will probably be wrong on someone else's computer, but you can get pretty close."

The existing answer is a bit brief and I had to flail around for a bit longer to actually get things working, so here's more detail:

/usr/bin/cargo run --color=always --package re5 --bin re5
   Compiling re5 v0.1.0 (file:///home/thoth/art/2019/radial-embroidery/re5)
error[E0432]: unresolved import `embroidery_stitcher`
 --> re5/src/main.rs:5:5
  |
5 | use embroidery_stitcher;
  |     ^^^^^^^^^^^^^^^^^^^ no `embroidery_stitcher` in the root

rustc --explain E0432 includes this paragraph that echos Shepmaster's answer:

Or, if you tried to use a module from an external crate, you may have missed the extern crate declaration (which is usually placed in the crate root):

 extern crate core; // Required to use the `core` crate use core::any; 

Switching from use to extern crate got me this:

/usr/bin/cargo run --color=always --package re5 --bin re5
   Compiling embroidery_stitcher v0.1.0 (file:///home/thoth/art/2019/radial-embroidery/embroidery_stitcher)
warning: function is never used: `svg_header`
 --> embroidery_stitcher/src/lib.rs:2:1
  |
2 | fn svg_header(w: i32, h: i32) -> String
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

   Compiling re5 v0.1.0 (file:///home/thoth/art/2019/radial-embroidery/re5)
error[E0603]: function `svg_header` is private
 --> re5/src/main.rs:8:19
  |
8 |     let mut svg = embroidery_stitcher::svg_header(100,100);
  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I had to slap a pub on the front of that function

pub fn svg_header(w: i32, h: i32) -> String

Now it works.