cargo fmt doesn't respect the passed files

[zimbatm]

cargo fmt parses the Cargo.toml and then generates its own list of files to format.

$ strace -f -e execve -s 4096 cargo fmt -- src/customlog.rs 
execve("/nix/store/lw6s4749i3z2kpg26742ivjcq746jvv2-devshell-dir/bin/cargo", ["cargo", "fmt", "--", "src/customlog.rs"], 0x7ffd5c548050 /* 82 vars */) = 0
execve("/nix/store/lw6s4749i3z2kpg26742ivjcq746jvv2-devshell-dir/bin/cargo-fmt", ["/nix/store/lw6s4749i3z2kpg26742ivjcq746jvv2-devshell-dir/bin/cargo-fmt", "fmt", "--", "src/customlog.rs"], 0x55be3c2d64c0 /* 85 vars */) = 0
strace: Process 3095549 attached
[pid 3095549] execve("/nix/store/fk9vq870hfgwj8w92r4zysvj3a52mzgh-rust/bin/cargo", ["/nix/store/fk9vq870hfgwj8w92r4zysvj3a52mzgh-rust/bin/cargo", "metadata", "--format-version", "1", "--no-deps", "--offline"], 0x7ffecc7ef7e0 /* 85 vars */) = 0
[pid 3095549] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3095549, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
strace: Process 3095550 attached
[pid 3095550] execve("/nix/store/lw6s4749i3z2kpg26742ivjcq746jvv2-devshell-dir/bin/rustfmt", ["rustfmt", "/home/zimbatm/go/src/github.com/numtide/prjfmt/src/lib.rs", "/home/zimbatm/go/src/github.com/numtide/prjfmt/src/main.rs", "--edition", "2018", "src/customlog.rs"], 0x7ffecc7ef7e0 /* 85 vars */) = 0
[pid 3095550] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3095550, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
+++ exited with 0 +++

You can see that 3095550 rustfmt is being invoked with the list of files of the project, plus the one passed as an argument.

[basile-henry]

I think it makes more sense to use rustfmt directly for Rust. cargo fmt is basically prjfmt for Rust (it uses rustfmt under the hood) 😄

[zimbatm]

I think so too. The only missing bit is to keep the --edition flag in sync with the Cargo.toml file.

[zimbatm]

I documented this briefly in docs/formatters.md . Let's add all the formatters and their support status there.

[domenkozar]

Kind of, when you have a mix of packages that use different editions, rustfmt isn't aware which crate uses what edition. See https://git.snix.dev/snix/snix/issues/115

[jfly]

Then it does sound like cargo fmt is useful to us, as it has more than just tree traversal logic in it.

I found this issue discussing this missing feature (the fact that you can't cargo fmt a single file) here: rust-lang/rustfmt#4485 (comment). Based on my reading of the conversation, it seems like they might be open to a change to cargo fmt that does respect the list of files given.

[domenkozar]

See rust-lang/rustfmt#5071