cargo run: can't find crate even though it's listed in Cargo.toml

user_11041613 0
Viewed 1362

I am using a Rust script called build.rs for code generation (it's not a Cargo build script). The script contains this at the top:

extern crate reqwest;

This is my Cargo.toml file:

[package]
name = "my-script"
version = "0.1.0"
edition = "2018"

[[bin]]
path = "build.rs"
name = "builder"

[dependencies]
reqwest = { version = "0.10", features = ["blocking", "json"] }

When I do cargo run, it gives me this error:

error[E0463]: can't find crate for `reqwest`
 --> build.rs:1:1
  |
1 | extern crate reqwest;
  | ^^^^^^^^^^^^^^^^^^^^^ can't find crate

How do I make it able to find the reqwest crate?

rust-cargo rust
2 Answers

build.rs is the default name for a Cargo build script, which is ran at build time to generate code, link in C libraries, etc.

Since cargo sees that you have a build.rs in your project directory, it assumes its a build script and tries to build it. However build scripts don't use the normal dependencies and instead use dependencies from the [build-dependencies] section of Cargo.toml. Since you don't have one, the reqwest crate isn't available to the build script.

Renaming the file is an obvious fix. However the convention is to put executables into the bin/ directory of your project (cargo will even automatically find files in there for you).

user_6466190

The build.rs script needs a different name. Rename build.rs to builder.rs and update Cargo.toml:

path = "builder.rs"

You can also remove extern crate reqwest statement because it's inferred by Cargo.

user_110416130
Related