Adding livecheck Formula DSL

Library/Homebrew/.rubocop.yml

@@ -46,6 +46,8 @@ Metrics/AbcSize:
 Metrics/BlockLength:
   Enabled: true
   Max: 1100
+  Exclude:
+    - 'test/formula_spec.rb'
 Metrics/BlockNesting:
   Enabled: true
   Max: 5

Library/Homebrew/formula.rb

@@ -12,6 +12,7 @@ require "build_environment"
 require "build_options"
 require "formulary"
 require "software_spec"
+require "livecheck"
 require "install_renamed"
 require "pkg_version"
 require "keg"
@@ -353,6 +354,16 @@ class Formula
   # @see .homepage=
   delegate homepage: :"self.class"
 
+  # The livecheck specification for the software.
+  # @method livecheck
+  # @see .livecheck=
+  delegate livecheck: :"self.class"
+
+  # Is a livecheck specification defined for the software?
+  # @method livecheckable?
+  # @see .livecheckable?
+  delegate livecheckable?: :"self.class"
+
   # The version for the currently active {SoftwareSpec}.
   # The version is autodetected from the URL and/or tag so only needs to be
   # declared if it cannot be autodetected correctly.
@@ -2186,6 +2197,13 @@ class Formula
     # <pre>homepage "https://www.example.com"</pre>
     attr_rw :homepage
 
+    # Whether a livecheck specification is defined or not.
+    # It returns true when a livecheck block is present in the {Formula} and
+    # false otherwise, and is used by livecheck.
+    def livecheckable?
+      @livecheckable == true
+    end
+
     # The `:startup` attribute set by {.plist_options}.
     # @private
     attr_reader :plist_startup
@@ -2628,6 +2646,26 @@ class Formula
       define_method(:test, &block)
     end
 
+    # @!attribute [w] livecheck
+    # Livecheck can be used to check for newer versions of the software.
+    # This method evaluates the DSL specified in the livecheck block of the
+    # {Formula} (if it exists) and sets the instance variables of a Livecheck
+    # object accordingly. This is used by brew livecheck to check for newer
+    # versions of the software.
+    #
+    # <pre>livecheck do
+    #   skip "Not maintained"
+    #   url "https://example.com/foo/releases"
+    #   regex /foo-(\d+(?:\.\d+)+)\.tar/
+    # end</pre>
+    def livecheck(&block)
+      @livecheck ||= Livecheck.new
+      return @livecheck unless block_given?
+
+      @livecheckable = true
+      @livecheck.instance_eval(&block)
+    end
+
     # Defines whether the {Formula}'s bottle can be used on the given Homebrew
     # installation.
     #

Library/Homebrew/livecheck.rb

@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+# Livecheck can be used to check for newer versions of the software.
+# The livecheck DSL specified in the formula is evaluated the methods
+# of this class, which set the instance variables accordingly. The
+# information is used by brew livecheck when checking for newer versions
+# of the software.
+class Livecheck
+  # The reason for skipping livecheck for the formula.
+  # e.g. `Not maintained`
+  attr_reader :skip_msg
+
+  def initialize
+    @regex = nil
+    @skip = false
+    @skip_msg = nil
+    @url = nil
+  end
+
+  # Sets the regex instance variable to the argument given, returns the
+  # regex instance variable when no argument is given.
+  def regex(pattern = nil)
+    return @regex if pattern.nil?
+
+    @regex = pattern
+  end
+
+  # Sets the skip instance variable to true, indicating that livecheck
+  # must be skipped for the formula. If an argument is given and present,
+  # its value is assigned to the skip_msg instance variable, else nil is
+  # assigned.
+  def skip(skip_msg = nil)
+    @skip = true
+    @skip_msg = skip_msg.presence
+  end
+
+  # Should livecheck be skipped for the formula?
+  def skip?
+    @skip
+  end
+
+  # Sets the url instance variable to the argument given, returns the url
+  # instance variable when no argument is given.
+  def url(val = nil)
+    return @url if val.nil?
+
+    @url = val
+  end
+
+  # Returns a Hash of all instance variable values.
+  def to_hash
+    {
+      "regex"    => @regex,
+      "skip"     => @skip,
+      "skip_msg" => @skip_msg,
+      "url"      => @url,
+    }
+  end
+end

Library/Homebrew/test/formula_spec.rb

@@ -698,6 +698,43 @@ describe Formula do
     expect(f1.test_fixtures("foo")).to eq(Pathname.new("#{HOMEBREW_LIBRARY_PATH}/test/support/fixtures/foo"))
   end
 
+  specify "#livecheck" do
+    f = formula do
+      url "https://brew.sh/test-1.0.tbz"
+      livecheck do
+        skip "foo"
+        url "https://brew.sh/test/releases"
+        regex(/test-(\d+(?:\.\d+)+)\.tbz/)
+      end
+    end
+
+    expect(f.livecheck.skip?).to be true
+    expect(f.livecheck.skip_msg).to eq("foo")
+    expect(f.livecheck.url).to eq("https://brew.sh/test/releases")
+    expect(f.livecheck.regex).to eq(/test-(\d+(?:\.\d+)+)\.tbz/)
+  end
+
+  describe "#livecheckable?" do
+    specify "no livecheck block defined" do
+      f = formula do
+        url "https://brew.sh/test-1.0.tbz"
+      end
+
+      expect(f.livecheckable?).to be false
+    end
+
+    specify "livecheck block defined" do
+      f = formula do
+        url "https://brew.sh/test-1.0.tbz"
+        livecheck do
+          regex(/test-(\d+(?:.\d+)+).tbz/)
+        end
+      end
+
+      expect(f.livecheckable?).to be true
+    end
+  end
+
   specify "dependencies" do
     f1 = formula "f1" do
       url "f1-1.0"

Library/Homebrew/test/livecheck_spec.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+require "livecheck"
+
+describe Livecheck do
+  subject(:livecheckable) { described_class.new }
+
+  describe "#regex" do
+    it "returns nil if unset" do
+      expect(livecheckable.regex).to be nil
+    end
+
+    it "returns the Regex if set" do
+      livecheckable.regex(/foo/)
+      expect(livecheckable.regex).to eq(/foo/)
+    end
+  end
+
+  describe "#skip" do
+    it "sets the instance variable skip to true and skip_msg to nil when the argument is not present" do
+      livecheckable.skip
+      expect(livecheckable.instance_variable_get(:@skip)).to be true
+      expect(livecheckable.instance_variable_get(:@skip_msg)).to be nil
+    end
+
+    it "sets the instance variable skip to true and skip_msg to the argument when present" do
+      livecheckable.skip("foo")
+      expect(livecheckable.instance_variable_get(:@skip)).to be true
+      expect(livecheckable.instance_variable_get(:@skip_msg)).to eq("foo")
+    end
+  end
+
+  describe "#skip?" do
+    it "returns the value of the instance variable skip" do
+      expect(livecheckable.skip?).to be false
+      livecheckable.skip
+      expect(livecheckable.skip?).to be true
+    end
+  end
+
+  describe "#url" do
+    it "returns nil if unset" do
+      expect(livecheckable.url).to be nil
+    end
+
+    it "returns the URL if set" do
+      livecheckable.url("foo")
+      expect(livecheckable.url).to eq("foo")
+    end
+  end
+
+  describe "#to_hash" do
+    it "returns a Hash of all instance variables" do
+      expect(livecheckable.to_hash).to eq({ "regex"=>nil, "skip"=>false, "skip_msg"=>nil, "url"=>nil })
+    end
+  end
+end