Help using dependencies

help
1

Hi everybody,

I'm running a really simple issue, but as a complete newbie to Rust I can't seem to figure it out. I'm trying to get a very simple one-liner going to log a statement using log4rs. To do so I've got the following Cargo.toml:

[package]
name = "rustexample"
version = "0.1.0"
authors = ["me@gmail.com"]

[dependencies]
log = "0.4.17"
log4rs = "1.2.0"

Then the following content in src/main.rs:

use log::info;
use log4rs;

fn main() {
    info!("Hello, world!");
}

If I use print!("Hello, world!") it works fine. When using cargo build I get the following error:

error[E0432]: unresolved import `log4rs`
 --> src/main.rs:2:5
  |
2 | use log4rs;
  |     ^^^^^^ no `log4rs` in the root

error: cannot determine resolution for the macro `info`
 --> src/main.rs:5:5
  |
5 |     info!("Hello, world!");
  |     ^^^^
  |
  = note: import resolution is stuck, try simplifying macro imports

I can imagine the second error is a result of the first one. I'm probably missing something very obvious, but I can't find it. Can anybody throw me a lifeline? :smiley:

2

You don't need to use top-level crate names. If all you want is to call info!(), then use log::info() is sufficient. Or use a fully-qualified name and no explicit import: log::info!().

By the way, the redundant/useless import shouldn't lead to an error. It's just a warning by default. For example, the identical code compiles and runs in the Playground.

3

Does your Cargo.toml not have an edition key set? If not you're using the old 2015 edition, which requires you to add extern crate crate_name; before you can use it.

I'm not sure why you wouldn't be getting the same error for the log crate though

1 Like
4

thank you for the quick reply, I was under the impression the warning was preventing it from running. I managed to get it working based on your solution, thanks a lot!

5

there's no 'edition' field in the Cargo.toml, this is the only content:

[package]
name = "project"
version = "0.1.0"
authors = ["me@gmail.com"]

[dependencies]
log = "0.4.17"
log4rs = "1.2.0"
6

Unless you're intentionally targeting the 2015 edition, you probably want to add edition = "2021" after the authors = ... line

2 Likes
7

That actually made it work correctly with the import, thanks a lot! 2015 is still the default for backwards compatibility I take it?

8

Yup! If you use cargo new it will automatically fill in the edition in the generated Cargo.toml

1 Like
9

That makes sense then, I manually constructed the Cargo.toml. Thanks a lot!

10

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