Load cask from API with fullname

This allows homebrew/cask/caskname
to work with the FromAPILoader.

Also, creates new constant to hold the
regex to validate main tap casks.

Library/Homebrew/api/cask-source.rb

@@ -10,8 +10,6 @@ module Homebrew
       class << self
         extend T::Sig
 
-        CASK_TOKEN_REGEX = %r{^(homebrew/cask/)?[a-z0-9\-_]+$}.freeze
-
         sig { params(token: String).returns(Hash) }
         def fetch(token)
           token = token.delete_prefix("homebrew/cask/")
@@ -21,7 +19,7 @@ module Homebrew
         sig { params(token: String).returns(T::Boolean) }
         def available?(token)
           # Sanity check before hitting the API
-          return false unless token.match?(CASK_TOKEN_REGEX)
+          return false unless token.match?(HOMEBREW_MAIN_TAP_CASK_REGEX)
 
           begin
             fetch token

Library/Homebrew/cask/cask_loader.rb

@@ -193,11 +193,16 @@ module Cask
       FLIGHT_STANZAS = [:preflight, :postflight, :uninstall_preflight, :uninstall_postflight].freeze
 
       def self.can_load?(ref)
-        Homebrew::API::Cask.all_casks.key? ref
+        return false unless Homebrew::EnvConfig.install_from_api?
+        return false unless ref.is_a?(String)
+        return false unless ref.match?(HOMEBREW_MAIN_TAP_CASK_REGEX)
+
+        token = ref.delete_prefix("homebrew/cask/")
+        Homebrew::API::Cask.all_casks.key?(token)
       end
 
       def initialize(token)
-        @token = token
+        @token = token.delete_prefix("homebrew/cask/")
         @path = CaskLoader.default_path(token)
       end
 
@@ -356,18 +361,12 @@ module Cask
         FromInstanceLoader,
         FromContentLoader,
         FromURILoader,
+        FromAPILoader,
         FromTapLoader,
         FromTapPathLoader,
         FromPathLoader,
       ].each do |loader_class|
-        next unless loader_class.can_load?(ref)
-
-        if loader_class == FromTapLoader && Homebrew::EnvConfig.install_from_api? &&
-           ref.start_with?("homebrew/cask/") && FromAPILoader.can_load?(ref)
-          return FromAPILoader.new(ref)
-        end
-
-        return loader_class.new(ref)
+        return loader_class.new(ref) if loader_class.can_load?(ref)
       end
 
       if Homebrew::EnvConfig.install_from_api? && !need_path && Homebrew::API::CaskSource.available?(ref)

Library/Homebrew/tap_constants.rb

@@ -5,6 +5,8 @@
 HOMEBREW_TAP_FORMULA_REGEX = %r{^([\w-]+)/([\w-]+)/([\w+-.@]+)$}.freeze
 # Match taps' casks, e.g. `someuser/sometap/somecask`
 HOMEBREW_TAP_CASK_REGEX = %r{^([\w-]+)/([\w-]+)/([a-z0-9\-_]+)$}.freeze
+# Match main cask taps' casks, e.g. `homebrew/cask/somecask` or `somecask`
+HOMEBREW_MAIN_TAP_CASK_REGEX = %r{^(homebrew/cask/)?[a-z0-9\-_]+$}.freeze
 # Match taps' directory paths, e.g. `HOMEBREW_LIBRARY/Taps/someuser/sometap`
 HOMEBREW_TAP_DIR_REGEX = %r{#{Regexp.escape(HOMEBREW_LIBRARY.to_s)}/Taps/(?<user>[\w-]+)/(?<repo>[\w-]+)}.freeze
 # Match taps' formula paths, e.g. `HOMEBREW_LIBRARY/Taps/someuser/sometap/someformula`