Here.
Here.
Environment: 1.43.1-alpine3.11
Clap: 3.0.0-beta.1
error: cannot produce proc-macro for 'clap_derive v3.0.0-beta.1' as the target 'x86_64-unknown-linux-musl' does not support these crate types
Build should be successful.
Alpine Linux, official Rust image.
Here.
@mrusme As a general rule, please avoid linking to someone's github.com/<user>/<repo>/master because master (and other tags/branches) are not permalinks. You push a new commit, and the link now points to another piece of code.
Ideally, you should copy-paste the relevant code into the issue. If you think that the code sample is too large, you can use permalinks:

As regards to the issue, this is a bug in rustc. The fix is already merged and will be released in 1.44.0.
The temporary workaround is to use this
RUSTFLAGS="-C target-feature=-crt-static" cargo build
instead of cargo build.
Or if you don't need the derive (and it looks like you don't), you can just switch it off with:
# Cargo.toml
[dependencies]
clap = { git = "...", default-features = false, features = ["std"] }
@CreepySkeleton thank you, Sir!
I'm a Sir, yay!