Cannot build actix-web 0.7.8 using Rust 1.25 on the Windows Subsystem for Linux

Question

I'm trying to play around with the "actix-web" crate using Cargo. I'm using the WSL version of Ubuntu on Windows 10.

Steps I ran:

• Install Cargo (and Rust with it) using sudo apt install cargo
• Created a project using cargo new hello
• Added actix-web = "0.7.8" under the [dependencies] in the Cargo.toml file
• Ran cargo run and got the following compile error:

error[E0658]: non-reference pattern used to match a reference (see issue #42640)
--> /home/ash/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.13.2/build.rs:375:9
    |
375 |     let (_, _, perlasm_format) = ASM_TARGETS.iter().find(|entry| {
    |         ^^^^^^^^^^^^^^^^^^^^^^ help: consider using a reference: `&(_, _, perlasm_format)`

error[E0658]: non-reference pattern used to match a reference (see issue #42640)
--> /home/ash/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.13.2/build.rs:674:9
    |
674 |     for (src, dst) in src_dst {
    |         ^^^^^^^^^^ help: consider using a reference: `&(src, dst)`

error[E0658]: non-reference pattern used to match a reference (see issue #42640)
--> /home/ash/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.13.2/build.rs:737:35
    |
737 |             RING_SRCS.iter().any(|(_, f)| cmp(f)) ||
    |                                   ^^^^^^ help: consider using a reference: `&(_, f)`

error[E0658]: non-reference pattern used to match a reference (see issue #42640)
--> /home/ash/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.13.2/build.rs:741:35
    |
741 |             RING_SRCS.iter().any(|(_, f)| cmp(f)) ||
    |                                   ^^^^^^ help: consider using a reference: `&(_, f)`

I tried using a wildcard dependency but I could not get it to work.

rustc is version 1.25.0
cargo is version 0.26.0

Answer 1

According to Actix-web's crate page, the latest version (0.7.8) requires Rust version 1.26.0 or higher. Based on your error message, it appears to be because they are taking advantage of some improvements made to pattern matching ergonomics in Rust 1.26.0.

You could roll back to an older version of actix-web — version 0.6.15 appears to be the latest which works in Rust 1.25.0. However, you're likely to run into similar problems with other libraries and I'd definitely recommend updating Rust instead, so that you can take advantage of the improvements too.

The easiest way to update the Rust toolchain, and keep it updated, is with Rustup.