rubocop --server speedups

[gurgeous]

Can we do more? (see #10706). Here's a simple benchmark script against rubocop-daemon:

#!/bin/bash

# note: brew install hyperfine
pkill -f "rubocop --server"
pkill -f rubocop-daemon
rm -rf $HOME/.cache/rubocop*
touch empty.rb

hyperfine --warmup 3 -i "./rubocop-daemon-wrapper empty.rb"
hyperfine --warmup 3 -i "rubocop --server empty.rb"

and the output on my M1:

Benchmark 1: ./rubocop-daemon-wrapper empty.rb
  Time (mean ± σ):      26.7 ms ±   1.9 ms    [User: 3.4 ms, System: 8.0 ms]
  Range (min … max):    25.2 ms …  44.7 ms    100 runs

Benchmark 1: rubocop --server empty.rb
  Time (mean ± σ):     198.3 ms ±   1.8 ms    [User: 100.5 ms, System: 87.1 ms]
  Range (min … max):   195.7 ms … 201.7 ms    15 runs

[gurgeous]

Example: we can save 10-15ms per run by not requiring rainbow (or only requiring when necessary)

[gurgeous]

I wonder if we can shave some time off of Cache.cache_root_dir_from_config. Only load yaml & erb if CacheRootDirectory is in the file contents? That would save another 20-30ms per client run if that string is not present.

[gurgeous]

Excellent! I love micro-optimizations. This kind of speedup makes a big difference for users IMO