Refactor method to remove extra tap requires

[apainintheneck]

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We were selectively requiring the tap.rb file in a few places for performance reasons. The main method we were referencing was the Tap.cmd_directories method which uses Pathname and the TAP_DIRECTORY constant internally. Tap.cmd_directories is mostly used in the Commands module and that is loaded very early on in the program so it made sense to move that command to that module. To facilitate that I moved the TAP_DIRECTORY constant to the top-level and renamed it to HOMEBREW_TAP_DIRECTORY. It now lies in the tap_constants.rb file.

A nice bonus of this refactor is that it speeds up loading external commands since the tap.rb file is no longer required by default in those cases.

$ hyperfine --parameter-list branch master,refactor-method-to-remove-extra-tap-requires --war
mup 5 --setup 'git switch {branch}' 'brew branch-compare -h'
Benchmark 1: brew branch-compare -h (branch = master)
  Time (mean ± σ):     869.5 ms ±   5.1 ms    [User: 506.0 ms, System: 333.7 ms]
  Range (min … max):   858.3 ms … 876.7 ms    10 runs
 
Benchmark 2: brew branch-compare -h (branch = refactor-method-to-remove-extra-tap-requires)
  Time (mean ± σ):     723.3 ms ±   5.7 ms    [User: 418.1 ms, System: 275.5 ms]
  Range (min … max):   713.6 ms … 733.1 ms    10 runs
 
Summary
  brew branch-compare -h (branch = refactor-method-to-remove-extra-tap-requires) ran
    1.20 ± 0.01 times faster than brew branch-compare -h (branch = master)

brew commands also gets a speed boost since Commands.commands no longer requires tap.rb.

$ hyperfine --parameter-list branch master,refactor-method-to-remove-extra-tap-requires --war
mup 5 --setup 'git switch {branch}' 'brew commands'
Benchmark 1: brew commands (branch = master)
  Time (mean ± σ):     875.6 ms ±   8.0 ms    [User: 512.5 ms, System: 332.6 ms]
  Range (min … max):   864.7 ms … 889.5 ms    10 runs
 
Benchmark 2: brew commands (branch = refactor-method-to-remove-extra-tap-requires)
  Time (mean ± σ):     723.4 ms ±   5.5 ms    [User: 420.1 ms, System: 274.2 ms]
  Range (min … max):   718.4 ms … 733.8 ms    10 runs
 
Summary
  brew commands (branch = refactor-method-to-remove-extra-tap-requires) ran
    1.21 ± 0.01 times faster than brew commands (branch = master)

Note: All benchmarks are on an old iMac so may not be as noticeable on newer machines.

Risks: It's possible that another file was counting on the inclusion of tap.rb somewhere else in the codebase and this causes a missing require error. We have no easy way to test for that that I'm aware of.

[apainintheneck]

To recap the main changes here are now:

• Tap::TAP_DIRECTORY -> HOMEBREW_TAP_DIRECTORY
• Tap.cmd_directories -> Commands.tap_cmd_directories

I checked that the old names aren't referenced in any of the core taps I have installed locally.

$ pwd
/usr/local/Homebrew/Library/Taps
$ git grep --no-index TAP_DIRECTORY
$ git grep --no-index cmd_directories
$ brew tap
apainintheneck/dev-utils
homebrew/aliases
homebrew/autoupdate
homebrew/bundle
homebrew/cask
homebrew/cask-versions
homebrew/command-not-found
homebrew/core
homebrew/services
homebrew/test-bot
lifepillar/appleii

[MikeMcQuaid]

This is great, wonderful work @apainintheneck 👏🏻.

Given how often these require changes sadly go 💥: let's hold off until after the next tag (which will be later today UK time, merge Tuesday UK time?)