Run rustfmt on batches of multiple files

[Alexendoo]

changelog: none

This gives cargo dev fmt a nice speed boost, down from 90s (because old) on my laptop and 120s (because windows) on my desktop to ~5s on both

250 at a time was to give windows a good amount of headroom (failed at ~800, rust-lang/rust#40384)

Also adds rustfmt to the toolchain file and has the clippy_dev workflow test using the pinned version as a follow up to #7963

[rust-highfive]

r? @camsteffen

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[camsteffen]

This was sorely needed, thanks! cargo dev fmt goes from 70s to 3.2s on my machine!

@bors r+

[bors]

📌 Commit 507030f has been approved by camsteffen

[bors]

⌛ Testing commit 507030f with merge cc9d7ff...

[flip1995]

Wait it took so long for you? It was only at 10s on every machine for me, so I didn't bother looking into it. 😄 Thanks so much for this!

[camsteffen]

I was surprised that it was that long. Has it gotten slower??

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: camsteffen
Pushing cc9d7ff to master...

[Alexendoo]

Now that you mention it the before numbers do seem a bit odd, I measured it after a rebase but it never felt like 2 minutes, more like 20-30s

[Alexendoo]

Surprisingly it got slower in 24d561f. Looks like rustup takes ~100ms extra if you don't manually specify the toolchain, which adds up over lots of tests

Benchmark 1: rustfmt --version
  Time (mean ± σ):     130.3 ms ±   2.0 ms    [User: 4.7 ms, System: 5.9 ms]
  Range (min … max):   127.1 ms … 133.7 ms    21 runs

Benchmark 2: rustfmt +nightly-2021-11-04 --version
  Time (mean ± σ):      37.5 ms ±   1.5 ms    [User: 2.7 ms, System: 8.4 ms]
  Range (min … max):    34.5 ms …  41.9 ms    58 runs

[flip1995]

Is this maybe a perf regression of rustfmt since 2021-11-04? Those numbers seem really high and would explain why it took up to 2 minutes.

[Alexendoo]

I believe it's not on rustfmt's end, it happens with rustc as well, here on stable (with no override/rust-toolchain file around)

Benchmark 1: rustc --version
  Time (mean ± σ):     135.8 ms ±   2.8 ms    [User: 4.3 ms, System: 7.7 ms]
  Range (min … max):   131.7 ms … 143.7 ms    19 runs

Benchmark 2: rustc +stable --version
  Time (mean ± σ):      44.0 ms ±   2.3 ms    [User: 5.3 ms, System: 8.6 ms]
  Range (min … max):    40.4 ms …  51.4 ms    55 runs

I plan to take a better look tomorrow

[Alexendoo]

I think it's down to rust-lang/rustup#2626