Only attempt to rustfmt files checked into git

[TheBlueMatt]

This avoids rustfmt failing on Rust files generated by dependent crates in target, eg

+ rustfmt --edition 2021 --check ./target/debug/build/thiserror-8230374e07b5c05a/out/probe.rs
Diff in /home/matt/rust-lightning-3/target/debug/build/thiserror-8230374e07b5c05a/out/probe.rs at line 1:

-    #![feature(provide_any)]
+#![feature(provide_any)]

-    use std::any::{Demand, Provider};
+use std::any::{Demand, Provider};

-    fn _f<'a, P: Provider>(p: &'a P, demand: &mut Demand<'a>) {
-        p.provide(demand);
-    }
+fn _f<'a, P: Provider>(p: &'a P, demand: &mut Demand<'a>) {
+	p.provide(demand);
+}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.64%. Comparing base (cdd1298) to head (930f5fb).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3327      +/-   ##
==========================================
- Coverage   89.64%   89.64%   -0.01%     
==========================================
  Files         126      126              
  Lines      102676   102676              
  Branches   102676   102676              
==========================================
- Hits        92043    92040       -3     
- Misses       7909     7912       +3     
  Partials     2724     2724              

☔ View full report in Codecov by Sentry.
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[vincenzopalazzo]

Probably something is breaking

Checking lightning-invoice v0.32.0 (/home/runner/work/rust-lightning/rust-lightning/lightning-invoice)
    Checking lightning v0.0.124 (/home/runner/work/rust-lightning/rust-lightning/lightning)
error: this function depends on never type fallback being `()`
    --> lightning/src/ln/chan_utils.rs:1405:2
     |
1405 |     fn read<R: io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
     = note: for more information, see issue #1[237](https://github.com/lightningdevkit/rust-lightning/actions/runs/10927675314/job/30334397040?pr=3327#step:5:238)48 <https://github.com/rust-lang/rust/issues/123748>
     = help: specify the types explicitly
note: in edition 2024, the requirement `!: util::ser::Readable` will fail
    --> lightning/src/util/ser_macros.rs:373:17
     |
373  |           $field = Some($crate::util::ser::Readable::read(&mut $reader)?);
     |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
    ::: lightning/src/ln/chan_utils.rs:1406:3
     |
1406 | /         _init_and_read_len_prefixed_tlv_fields!(reader, {
1407 | |             (0, commitment_number, required),
1408 | |             (1, to_broadcaster_delay, option),
1409 | |             (2, to_broadcaster_value_sat, required),
...    |
1416 | |             (15, channel_type_features, option),
1417 | |         });
     | |__________- in this macro invocation
     = note: `-D dependency-on-unit-never-type-fallback` implied by `-D warnings`
     = help: to override `-D warnings` add `#[allow(dependency_on_unit_never_type_fallback)]`
     = note: this error originates in the macro `$crate::_decode_tlv` which comes from the expansion of the macro `_init_and_read_len_prefixed_tlv_fields` (in Nightly builds, run with -Z macro-backtrace for more info)

error: using `map_err` over `inspect_err`
    --> lightning/src/ln/channelmanager.rs:4116:5
     |
4116 |         ).map_err(|e| {
     |           ^^^^^^^
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
     = note: `-D clippy::manual-inspect` implied by `-D warnings`
     = help: to override `-D warnings` add `#[allow(clippy::manual_inspect)]`
help: try
     |
4116 ~         ).inspect_err(|e| {
4117 |             let logger = WithContext::from(&self.logger, Some(path.hops.first().unwrap().pubkey), None, Some(*payment_hash));
4118 ~             log_error!(logger, "Failed to build an onion for path for payment hash {}", payment_hash);
     |

error: using `map_err` over `inspect_err`
   --> lightning/src/ln/outbound_payment.rs:773:5
    |
773 |             .map_err(|e| { self.remove_outbound_if_all_failed(payment_id, &e); e })
    |              ^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
help: try
    |
773 -             .map_err(|e| { self.remove_outbound_if_all_failed(payment_id, &e); e })
773 +             .inspect_err(|e| { self.remove_outbound_if_all_failed(payment_id, e); })
    |

error: could not compile `lightning` (lib) due to 3 previous errors

[TheBlueMatt]

Yes, linting will be broken until #3301 (due to rustc upgrade)

[tnull]

LGTM, but also looking forward to be able to just drop all of this and start using cargo fmt soon :)