Rust `unresolved import` on third party library - import

Question

I want to compile a simple rust program using a third party library named warp:
[package]
name = "hello-world-warp"
version = "0.1.0"
[dependencies]
warp = "0.1.18"
In src/main.rs:
use warp::{self, path, Filter};
fn main() {
// GET /hello/warp => 200 OK with body "Hello, warp!"
let hello = warp::path!("hello" / String)
.map(|name| format!("Hello, {}!", name));
warp::serve(hello)
.run(([127, 0, 0, 1], 3030));
}
When I run cargo build I see it download warp and lots of transitive dependencies, then I get the errors:
Compiling hello-world-warp v0.1.0 (<path>) error[E0432]: unresolved import `warp`
--> src/main.rs:3:12
|
3 | use warp::{self, path, Filter};
| ^^^^ no `warp` in the root
error: cannot find macro `path!` in this scope
I've gone through various docs on modules and crates. What am I doing wrong in this simple scenario?

Answer 1

The example you copied uses a syntax that works in the most recent edition of Rust, but you've accidentally set your Rust to emulate an old "2015" version of the language.
You must add:
edition = "2018"
to your Cargo.toml's [package] section.
When starting new projects, always use cargo new. It will ensure the latest edition flag is set correctly.