unversioned_cask_checker: check installer artifacts

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

@@ -106,4 +106,12 @@ describe Homebrew::Livecheck::Strategy::ExtractPlist do
         .to raise_error(TypeError, Homebrew::Livecheck::Strategy::INVALID_BLOCK_RETURN_VALUE_MSG)
     end
   end
+
+  describe "::find_versions" do
+    it "can be used with an installer artifact" do
+      cask = Cask::CaskLoader.load(cask_path("livecheck/installer-manual-livecheck"))
+
+      expect(extract_plist.find_versions(cask: cask)[:matches].values).to eq(["1.2.3"])
+    end
+  end
 end

Library/Homebrew/test/support/fixtures/cask/Casks/livecheck/installer-manual-livecheck.rb

@@ -0,0 +1,16 @@
+cask "installer-manual-livecheck" do
+  version "1.2.3"
+  sha256 "67cdb8a02803ef37fdbf7e0be205863172e41a561ca446cd84f0d7ab35a99d94"
+
+  url "file://#{TEST_FIXTURE_DIR}/cask/caffeine.zip"
+  name "With Installer Manual"
+  desc "Cask with a manual installer"
+  homepage "https://brew.sh/"
+
+  livecheck do
+    url :url
+    strategy :extract_plist
+  end
+
+  installer manual: "Caffeine.app"
+end

Library/Homebrew/unversioned_cask_checker.rb

@@ -36,6 +36,11 @@ module Homebrew
       @qlplugins ||= @cask.artifacts.select { |a| a.is_a?(Cask::Artifact::Qlplugin) }
     end
 
+    sig { returns(T::Array[Cask::Artifact::Installer]) }
+    def installers
+      @installers ||= @cask.artifacts.select { |a| a.is_a?(Cask::Artifact::Installer) }
+    end
+
     sig { returns(T::Array[Cask::Artifact::Pkg]) }
     def pkgs
       @pkgs ||= @cask.artifacts.select { |a| a.is_a?(Cask::Artifact::Pkg) }
@@ -88,8 +93,9 @@ module Homebrew
 
         installer.extract_primary_container(to: dir)
 
-        info_plist_paths = apps.concat(qlplugins).flat_map do |artifact|
+        info_plist_paths = apps.concat(qlplugins, installers).flat_map do |artifact|
-          top_level_info_plists(Pathname.glob(dir/"**"/artifact.source.basename/"Contents"/"Info.plist")).sort
+          source = artifact.is_a?(Cask::Artifact::Installer) ? artifact.path : artifact.source.basename
+          top_level_info_plists(Pathname.glob(dir/"**"/source/"Contents"/"Info.plist")).sort
         end
 
         info_plist_paths.each(&parse_info_plist)