livecheck: add GithubLatest strategy

Library/Homebrew/livecheck/strategy.rb

@@ -78,6 +78,7 @@ end
 require_relative "strategy/apache"
 require_relative "strategy/bitbucket"
 require_relative "strategy/git"
+require_relative "strategy/github_latest"
 require_relative "strategy/gnome"
 require_relative "strategy/gnu"
 require_relative "strategy/hackage"

Library/Homebrew/livecheck/strategy/github_latest.rb

@@ -0,0 +1,59 @@
+# typed: false
+# frozen_string_literal: true
+
+module Homebrew
+  module Livecheck
+    module Strategy
+      # The {GithubLatest} strategy identifies versions of software at
+      # github.com by checking a repository's latest release page.
+      #
+      # GitHub URLs take a few differemt formats:
+      #
+      # * `https://github.com/example/example/releases/download/1.2.3/example-1.2.3.zip`
+      # * `https://github.com/example/example/archive/v1.2.3.tar.gz`
+      #
+      # This strategy is used when latest releases are marked for software hosted
+      # on GitHub. It is necessary to use `strategy :github_latest` in a `livecheck`
+      # block for Livecheck to use this strategy.
+      #
+      # The default regex identifies versions from `href` attributes containing the
+      # tag name.
+      #
+      # @api public
+      class GithubLatest
+        NICE_NAME = "GitHub Latest"
+
+        # The `Regexp` used to determine if the strategy applies to the URL.
+        URL_MATCH_REGEX = /github.com/i.freeze
+
+        # Whether the strategy can be applied to the provided URL.
+        #
+        # @param url [String] the URL to match against
+        # @return [Boolean]
+        def self.match?(url)
+          URL_MATCH_REGEX.match?(url)
+        end
+
+        # Generates a URL and regex (if one isn't provided) and passes them
+        # to {PageMatch.find_versions} to identify versions in the content.
+        #
+        # @param url [String] the URL of the content to check
+        # @param regex [Regexp] a regex used for matching versions in content
+        # @return [Hash]
+        def self.find_versions(url, regex = nil)
+          %r{github\.com/(?<username>[\da-z\-]+)/(?<repository>[\da-z_\-]+)}i =~ url
+
+          # The page containing the latest release
+          page_url = "https://github.com/#{username}/#{repository}/releases/latest"
+
+          # The default regex applies to most repositories, but may have to be
+          # replaced with a specific regex when the tag names contain the package
+          # name or other characters apart from the version.
+          regex ||= %r{href=.*?/tag/v?(\d+(?:\.\d+)+)["' >]}i
+
+          Homebrew::Livecheck::Strategy::PageMatch.find_versions(page_url, regex)
+        end
+      end
+    end
+  end
+end

Library/Homebrew/test/livecheck/strategy/github_latest_spec.rb

@@ -0,0 +1,26 @@
+# typed: false
+# frozen_string_literal: true
+
+require "livecheck/strategy/github_latest"
+
+describe Homebrew::Livecheck::Strategy::GithubLatest do
+  subject(:github_latest) { described_class }
+
+  let(:github_download_url) { "https://github.com/example/example/releases/download/1.2.3/example-1.2.3.zip" }
+  let(:github_archive_url) { "https://github.com/example/example/archive/v1.2.3.tar.gz" }
+  let(:non_github_url) { "https://brew.sh/test" }
+
+  describe "::match?" do
+    it "returns true if the argument provided is a GitHub Download URL" do
+      expect(github_latest.match?(github_download_url)).to be true
+    end
+
+    it "returns true if the argument provided is a GitHub Archive URL" do
+      expect(github_latest.match?(github_archive_url)).to be true
+    end
+
+    it "returns false if the argument provided is not a GitHub URL" do
+      expect(github_latest.match?(non_github_url)).to be false
+    end
+  end
+end