Separate the Ruby backend from internal Homebrew dependencies

[rolandwalker]

Background

Homebrew-cask is implemented as a Homebrew external command, in the form of
brew-cask.rb, which is required by the brew command. This means that
Homebrew-cask has full access to, and is constrained by, the Ruby runtime
provided by Homebrew.

Initially it was thought that Homebrew-cask would re-use much of Homebrew's
code internally. That turned out not to be the case in practice, largely
because Homebrew's code is organized around the Formula.

Proposal

brew-cask.rb should be re-implemented as an executable brew-cask, which
would be invoked by Homebrew rather than required. brew-cask would
then execute completely independently of Homebrew's Ruby environment.

This would be an internal-only change. The user interface would stay the
same. Commands would still be invoked via brew cask <verb>, and we would
still piggyback on brew update to get new Casks.

Advantages

• Stability. Homebrew does not guarantee any internal APIs.
  Homebrew-cask frequently breaks due to changes within Homebrew
  (force UTF-8 encodings #4732, Adjust to Homebrew's test environment changes #4982, Defend against unusual Homebrew setups #4229, many others).
• Clarity. Where we do re-use Homebrew's classes (such as for
  downloading), we do so only partially, with some methods overridden.
  This needlessly obscures what the code is doing, making it more difficult
  to diagnose bugs or develop new functionality.
• Error Reporting. Both Homebrew and Homebrew-cask attempt to
  rescue exceptions and direct users to the relevant issues URL. @voanhduy1512
  did some good work on this problem, but it still crops up as in Update error #5108. Every
  misdirected report is a drain on maintainers (in both projects).
• Cleanup. Currently brew cask cleanup works in a roundabout
  way (using tracking symlinks) because we share a download location
  with Homebrew. It would be more robust to maintain our own download
  cache.
• Ruby 2.0. We would have the choice to be more aggressive about
  switching to Ruby 2.0 (say, 6 months after Yosemite is released). We
  could require Mountain Lion and earlier to install Ruby 2.0 as a
  prerequisite. This would not only gain us access to new language
  features, but reduce the currently-imposed burden of maintaining
  compatibility across Ruby 1.8 and 2.0.
• Freedom. Currently we are constrained by Homebrew's decisions with
  regard to character encodings, interpreter version, monkeypatching -- all
  things that, once inherited, we cannot easily undo.

Disadvantages

• Tap Migration. We have sometimes used internal interfaces to Homebrew
  which are not available externally, as with the tap migration code (automatically transition to new Tap name/location #4169).
  However, this also could have been accomplished by copying the relevant
  logic from Homebrew.
• Integration for files in /usr/local. Some Casks install files into /usr/local,
  which causes brew doctor to complain as in Installing truecrypt makes 'brew doctor' unhappy #2350 and others. Currently
  we have a caveats warning for this, which is not really a fix. As mentioned
  in Cleanup after Truecrypt installation #3693, we could fully resolve the problem by installing files to a Homebrew
  Cellar, and then symlinking into the Cellar as with any other Homebrew
  installation. Such a technique would become more difficult if we could not
  call directly into Homebrew.
  • However, it also seems that nobody is working on that implementation.
  • There are other possible approaches, such as generating an ad hoc Formula.

Places where we currently re-use Homebrew's code (incomplete)

• global methods such as onoe (example install.rb)
  • these are mostly trivial
  • relevant code would have to be forked from Homebrew
  • in some cases, we can simplify and/or get more desirable behavior
• monkeypatched methods on Pathname ?
  • preferable to remove these where they may exist
  • we at least use our own variant monkeypatch cabv (fork abv method with better odd-filename defense #2991)
• implicit tapping (handle fully-qualified cask names, fixes #2235 #2303)
  • can be replaced by invoking brew tap <Tapname>
• downloading, eg Cask::CurlDownloadStrategy (see comments in download_strategy.rb)
  • relevant code would have to be forked from Homebrew
• calculation of checksums
  • would be simplified, as our project only uses one checksum type
• depends_on_formula (add dependencies for Homebrew formulae #2305)
  • can be replaced by invoking brew install <formula>
• automatic tap migration (automatically transition to new Tap name/location #4169)
  • this code was meant to be temporary in any case
• test suite
  • we have also been discussing rearchitecting the test suite to use RSpec

Tracker

• Wait until Tap migration code can be safely removed (minimum of 90 days,
  roughly 3 August.)
• Convert brew-cask.rb to a bash-script executable shim brew-cask (Separate the Ruby backend from Homebrew + Require Ruby 2.x #8089)
• Update Formula brew-cask.rb (a different file) to support the new setup (Separate the Ruby backend from Homebrew + Require Ruby 2.x #8089)
• Fork and check in all Homebrew code needed for tests to pass (Separate the Ruby backend from Homebrew + Require Ruby 2.x #8089)
• Refactor: integrate all needed classes & methods organically in our codebase
  • remove Homebrew internal method in Cask::CLI::Update #8155
  • strip from homebrew-fork: dependencies and reqs #8158
  • remove from homebrew-fork all code related to bottles #8188
  • port PrettyListing class from Homebrew-fork #8189
  • remove homebrew-fork file tap_migrations.rb #8194
  • remove patch.rb from homebrew-fork #8195
  • remove install_renamed.rb from homebrew-fork #8196
  • remove debrew.rb from homebrew-fork #8197
  • remove several homebrew-fork files #8218
  • Adjust brew cask doctor for homebrew-fork #8221
  • remove homebrew-fork software_spec.rb #8225
  • remove cxxstdlib.rb from homebrew-fork #8226
  • remove homebrew-fork compat.rb and compat dir #8227
  • remove linux compat from homebrew-fork #8228
  • remove inreplace.rb from homebrew-fork #8229
  • remove tap_constants.rb from homebrew-fork #8230
  • remove several more Homebrew-fork files #8247
  • strip various exception classes from homebrew-fork #8261
  • remove ENV/super.rb from homebrew-fork #8263
  • Homebrew strip test env #8264
  • remove metafiles.rb from homebrew-fork #8265
  • remove compilers.rb from homebrew-fork #8266
  • remove homebrew-fork extend/ENV.rb #8268
  • remove Ruby 2.0 forward-ports from homebrew-fork #8295
  • remove methods from homebrew-cask extend/string.rb #8296
  • remove extend/module from homebrew-fork #8297
  • strip methods from homebrew-fork extend/ARGV.rb #8298
  • remove xcode.rb from homebrew-fork #8308
  • strip classes from homebrew-fork download_strategy.rb #8310
  • remove os.rb from homebrew-fork #8312
  • Strip compiler methods from homebrew-fork OS::Mac #8314
  • adopt lib/vendor structure #8328
  • remove mach.rb from homebrew-fork #8329
  • delete homebrew-fork code specific to old Rubies #8330
  • remove homebrew-fork module ObserverPathnameExtension #8331
  • remove numerous unused methods from homebrew-fork #8332
  • pare back homebrew-fork global.rb #8333
  • adopt okjson.rb from homebrew-fork #8334
  • move mktemp method into homebrew-fork resource.rb #8335
  • remove String monkeypatches: start_with? and undent_…_72 #8336
  • remove homebrew-fork extend/fileutils.rb #8337
  • remove homebrew-fork chuzzle method #8338
  • remove homebrew-fork staging logic #8339
  • remove homebrew-fork with_system_path method #8340
  • fully remove homebrew-fork mach.rb #8341
  • delete ~75% of homebrew-fork extend/pathname.rb #8342
  • Remove rogue include of homebrew-fork FileUtils #8361
  • remove Homebrew namespaces in homebrew-fork #8369
  • Remove homebrew-fork Checksum class and refactor #8388
  • add requires removed during homebrew-fork cleanups #8389
  • remove homebrew-fork class Tty #8390
  • strip more unused methods from homebrew-fork extend/pathname.rb #8391
  • remove homebrew-fork extend/string.rb #8392
  • remove some unused methods from homebrew-fork os/mac.rb #8393
  • Refactor Homebrew's Tty class #8402
  • Strip homebrew-fork extend/pathname.rb #8403
  • strip homebrew-fork utils.rb #8425
  • remove homebrew-fork extend Pathname#version #8426
  • rm homebrew-fork extend Pathname#rmdir_if_possible #8427
  • remove homebrew-fork Pathname#/ monkeypatch #8428
  • remove homebrew-fork ARGV monkeypatch #8433
  • remove unused homebrew-fork method popen_write #8434
  • remove unused constants/methods from hardware.rb #8435
  • remove 3 unused methods from download_strategy.rb #8436
  • remove namespace workaround from homebrew-fork #8437
  • remove homebrew-fork Version class #8446
  • remove homebrew-fork GitHub class #8447
  • remove JSON support from homebrew-fork #8448
  • move Hash monkeypatch to separate file #8458
  • move cabv method out of Pathname monkeypatch #8460
  • don't monkeypatch MacOS#release #8461
  • remove homebrew-fork os/mac/hardware.rb #8464
  • Strip instruction set detection methods from homebrew-fork #8466
  • don't redirect tput STDERR #8522
  • incorporate a modified homebrew-fork OS::Mac into our codebase as Cask::MacOS #8539
  • remove homebrew-fork xquartz.rb #8552
  • flatten homebrew-fork and move it under vendor/lib #8556
  • incorporate hardware.rb from homebrew-fork #8557
  • migrate puts_columns from homebrew-fork into our codebase. #8559
  • Rewrite homebrew-fork which method #8561
  • remove homebrew-fork resource.rb #8595
  • replace homebrew-fork method exec_editor #8611
  • strip homebrew-fork download_strategy.rb #8612
  • partial merge of homebrew-fork download_strategy #8721
  • incorporate homebrew-fork ignore_interrupts utility method #8724
  • remove homebrew-fork MACOS_RELEASE constants #8870
  • make Hbc::SystemCommand safe for commands with large writes to STDERR as performed by curl
  • execute curl via Hbc::SystemCommand, migrating it out of homebrew-fork
  • migrate Hbc::HbCurlDownloadStrategy from homebrew-fork
  • Hbc::HbSubversionDownloadStrategy cleanups
    • remove shell_quote method
    • use Hbc::SystemCommand instead of quiet_system
    • use Hbc::SystemCommand instead of backticks
  • migrate Hbc::HbSubversionDownloadStrategy from homebrew-fork
  • migrate Hbc::HbVCSDownloadStrategy from homebrew-fork
  • revise download caching
    • create our own cache at /Library/Caches/Homebrew-cask, setting value in Hbc::Locations
    • remove HOMEBREW_CACHE constant from global.rb
    • remove HOMEBREW_CACHE constant from testing_env.rb, and inject a test value for both rspec and minitest
    • transitional code: at startup, automatically purge all old files tracked by /Library/Caches/Homebrew/Casks, if seen
    • simplify brew cask cleanup (no longer needs to use subdirectory and tracking symlinks)
  • delete homebrew-fork download_strategy.rb
  • delete homebrew-fork exceptions.rb
  • delete homebrew-fork global.rb
  • delete homebrew-fork monkeypatch_pathname.rb
  • delete homebrew-fork testing_env.rb
  • delete homebrew-fork utils.rb
• delete directory lib/vendor/homebrew-fork

Edits:

• added Disadvantage / Integration for files in /usr/local
• added Tracker
• added Error Reporting
• renamed Plan to Tracker; filled out Tracker details

[muescha]

and add:

Advantages:
standalone: just install cask without the need to install brew

[vitorgalvao]

just install cask without the need to install brew

Not exactly. From the post:

we would still piggyback on brew update to get new Casks.

[muescha]

if brew is in stalled then piggyback on brew update and for without brew add a cask update

[rolandwalker]

cc @phinze

[vitorgalvao]

@jawshooah Since we now want to go in the opposite direction, should we close this, or is it still useful in some way?

[jawshooah]

No use in leaving it open.