api_hashable: Make API path subs generic

This turns the ability to replace common paths with placeholders
into a mixin that can be used with both Casks and Formulae.

The idea here is to make formula hash generation more consistent.

Library/Homebrew/cask/cask.rb

@@ -6,6 +6,7 @@ require "cask/config"
 require "cask/dsl"
 require "cask/metadata"
 require "utils/bottles"
+require "extend/api_hashable"
 
 module Cask
   # An instance of a cask.
@@ -16,11 +17,9 @@ module Cask
 
     extend Forwardable
     extend Predicable
+    extend APIHashable
     include Metadata
 
-    # Needs a leading slash to avoid `File.expand.path` complaining about non-absolute home.
-    HOME_PLACEHOLDER = "/$HOME"
-    HOMEBREW_PREFIX_PLACEHOLDER = "$HOMEBREW_PREFIX"
     APPDIR_PLACEHOLDER = "$APPDIR"
 
     # TODO: can be removed when API JSON is regenerated with HOMEBREW_PREFIX_PLACEHOLDER.
@@ -31,37 +30,6 @@ module Cask
 
     attr_predicate :loaded_from_api?
 
-    class << self
-      def generating_hash!
-        return if generating_hash?
-
-        # Apply monkeypatches for API generation
-        @old_homebrew_prefix = HOMEBREW_PREFIX
-        @old_home = Dir.home
-        Object.send(:remove_const, :HOMEBREW_PREFIX)
-        Object.const_set(:HOMEBREW_PREFIX, Pathname(HOMEBREW_PREFIX_PLACEHOLDER))
-        ENV["HOME"] = HOME_PLACEHOLDER
-
-        @generating_hash = true
-      end
-
-      def generated_hash!
-        return unless generating_hash?
-
-        # Revert monkeypatches for API generation
-        Object.send(:remove_const, :HOMEBREW_PREFIX)
-        Object.const_set(:HOMEBREW_PREFIX, @old_homebrew_prefix)
-        ENV["HOME"] = @old_home
-
-        @generating_hash = false
-      end
-
-      def generating_hash?
-        @generating_hash ||= false
-        @generating_hash == true
-      end
-    end
-
     def self.all
       # TODO: ideally avoid using ARGV by moving to e.g. CLI::Parser
       if ARGV.exclude?("--eval-all") && !Homebrew::EnvConfig.eval_all?

Library/Homebrew/cask/cask_loader.rb

@@ -329,8 +329,8 @@ module Cask
         # TODO: HOMEBREW_OLD_PREFIX_PLACEHOLDER can be removed when API JSON is
         #       regenerated with HOMEBREW_PREFIX_PLACEHOLDER.
         string.to_s
-              .gsub(Cask::HOME_PLACEHOLDER, Dir.home)
-              .gsub(Cask::HOMEBREW_PREFIX_PLACEHOLDER, HOMEBREW_PREFIX)
+              .gsub(HOMEBREW_HOME_PLACEHOLDER, Dir.home)
+              .gsub(HOMEBREW_PREFIX_PLACEHOLDER, HOMEBREW_PREFIX)
               .gsub(Cask::APPDIR_PLACEHOLDER, appdir)
               .gsub(Cask::HOMEBREW_OLD_PREFIX_PLACEHOLDER, HOMEBREW_PREFIX)
       end

Library/Homebrew/dev-cmd/generate-formula-api.rb

@@ -50,6 +50,7 @@ module Homebrew
     FileUtils.mkdir_p directories
 
     Formulary.enable_factory_cache!
+    Formula.generating_hash!
 
     tap.formula_names.each do |name|
       formula = Formulary.factory(name)

Library/Homebrew/extend/api_hashable.rb

@@ -0,0 +1,34 @@
+# typed: true
+# frozen_string_literal: true
+
+# Used to substitute common paths with generic placeholders when generating JSON for the API.
+module APIHashable
+  def generating_hash!
+    return if generating_hash?
+
+    # Apply monkeypatches for API generation
+    @old_homebrew_prefix = HOMEBREW_PREFIX
+    @old_home = Dir.home
+    Object.send(:remove_const, :HOMEBREW_PREFIX)
+    Object.const_set(:HOMEBREW_PREFIX, Pathname.new(HOMEBREW_PREFIX_PLACEHOLDER))
+    ENV["HOME"] = HOMEBREW_HOME_PLACEHOLDER
+
+    @generating_hash = true
+  end
+
+  def generated_hash!
+    return unless generating_hash?
+
+    # Revert monkeypatches for API generation
+    Object.send(:remove_const, :HOMEBREW_PREFIX)
+    Object.const_set(:HOMEBREW_PREFIX, @old_homebrew_prefix)
+    ENV["HOME"] = @old_home
+
+    @generating_hash = false
+  end
+
+  def generating_hash?
+    @generating_hash ||= false
+    @generating_hash == true
+  end
+end

Library/Homebrew/formula.rb

@@ -30,6 +30,7 @@ require "find"
 require "utils/spdx"
 require "extend/on_system"
 require "api"
+require "extend/api_hashable"
 
 # A formula provides instructions and metadata for Homebrew to install a piece
 # of software. Every Homebrew formula is a {Formula}.
@@ -69,6 +70,7 @@ class Formula
   extend Forwardable
   extend Cachable
   extend Predicable
+  extend APIHashable
 
   # The name of this {Formula}.
   # e.g. `this-formula`

Library/Homebrew/global.rb

@@ -58,6 +58,8 @@ HOMEBREW_MACOS_ARM_DEFAULT_REPOSITORY = ENV.fetch("HOMEBREW_MACOS_ARM_DEFAULT_RE
 HOMEBREW_LINUX_DEFAULT_PREFIX = ENV.fetch("HOMEBREW_LINUX_DEFAULT_PREFIX").freeze
 HOMEBREW_LINUX_DEFAULT_REPOSITORY = ENV.fetch("HOMEBREW_LINUX_DEFAULT_REPOSITORY").freeze
 HOMEBREW_PREFIX_PLACEHOLDER = "$HOMEBREW_PREFIX"
+# Needs a leading slash to avoid `File.expand.path` complaining about non-absolute home.
+HOMEBREW_HOME_PLACEHOLDER = "/$HOME"
 
 HOMEBREW_MACOS_NEWEST_UNSUPPORTED = ENV.fetch("HOMEBREW_MACOS_NEWEST_UNSUPPORTED").freeze
 HOMEBREW_MACOS_OLDEST_SUPPORTED = ENV.fetch("HOMEBREW_MACOS_OLDEST_SUPPORTED").freeze

Library/Homebrew/test/cask/cask_spec.rb

@@ -337,6 +337,8 @@ describe Cask::Cask, :cask do
       expect(JSON.pretty_generate(h["variations"])).to eq expected_sha256_variations.strip
     end
 
+    # @note The calls to `APIHashable.generating_hash!` and `APIHashable.generated_hash!`
+    #   are not idempotent so they can only be used in one test.
     it "returns the correct hash placeholders" do
       described_class.generating_hash!
       expect(described_class).to be_generating_hash