rust-rustfmt-switches from .dir-local.el

[andrewzhurov]

In rust-mode 1.0.6 setting rust-rustfmt-switches in .dir-locals.el has no effect.
E.g., ("--edition" "2024) gets disregarded. (value that's been set globally gets read on save, in my case it was ("--edition" "2018").

It seems possible to configure rust-fmt per-project by setting nil, in which case it reads config from rustfmt.toml, and that's the default now.
Still, may be nice to allow per-project configuration via .dir-locals.el?

[psibi]

(value that's been set globally gets read on save, in my case it was ("--edition" "2018")

Where does it set globally ?

It is intentional that for per project settings, we prefer using rustfmt.toml now. There was a discussion about it in this PR: #571

That being said, if you set rust-rustfmt-switches, rust-mode still respects it and will pass that option. Can you give a small way to reproduce it if that's the case ?

[andrewzhurov]

Where does it set globally ?

In my case it was from rust-rustfmt.el (since I'm using a bit stale version).

(defcustom rust-rustfmt-switches '("--edition" "2018")
  "Arguments to pass when invoking the `rustfmt' executable."
  :type '(repeat string)
  :group 'rust-mode)

I suspect the same effect will be by setting variable manually, e.g., via M-x set-variable, or in init.el.

E.g., here I manually set to 2018, .dir-locals set it to 2024.
describe-variable:

Its value is ("--edition" "2024")
Original value was 
("--edition" "2018")
Local in buffer adapter.rs; global value is 
("--edition" "2018")

Then, e.g., on save in this file an error pops

error: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an operator, found `"android/bluetooth/BluetoothManager"`
  --> adapter.rs:99:61
   |
99 |                     Local::from_raw(env, env.require_class(c"android/bluetooth/BluetoothManager"));
   |                                                             -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                                                             |
   |                                                             expected one of 8 possible tokens
   |                                                             help: missing `,`
   |
   = note: you may be trying to write a c-string literal
   = note: c-string literals require Rust 2021 or later
   = help: pass `--edition 2024` to `rustc`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide

(that option to read from rustfmt.toml is nice, scratches the same itch, feel free to close this issue if that's the intended way to have per-project config)