livecheck: refactor HEAD-only formula handling

Library/Homebrew/cask/dsl.rb

@@ -287,6 +287,7 @@ def container(**kwargs)
     #
     # @see DSL::Version
     # @api public
+    sig { params(arg: T.nilable(T.any(String, Symbol))).returns(T.nilable(DSL::Version)) }
     def version(arg = nil)
       set_unique_stanza(:version, arg.nil?) do
         if !arg.is_a?(String) && arg != :latest

Library/Homebrew/formula.rb

@@ -2403,6 +2403,7 @@ def any_installed_prefix
 
   # Returns the {PkgVersion} for this formula if it is installed.
   # If not, return `nil`.
+  sig { returns(T.nilable(PkgVersion)) }
   def any_installed_version
     any_installed_keg&.version
   end

Library/Homebrew/keg.rb

@@ -388,6 +388,7 @@ def elisp_installed?
     (path/"share/emacs/site-lisp"/name).children.any? { |f| ELISP_EXTENSIONS.include? f.extname }
   end
 
+  sig { returns(PkgVersion) }
   def version
     require "pkg_version"
     PkgVersion.parse(path.basename.to_s)

Library/Homebrew/livecheck/livecheck.rb

@@ -13,6 +13,9 @@
   # command. These methods print the requested livecheck information
   # for formulae.
   module Livecheck
+    NO_CURRENT_VERSION_MSG = "Unable to identify current version"
+    NO_VERSIONS_MSG = "Unable to get versions"
+
     UNSTABLE_VERSION_KEYWORDS = T.let(%w[
       alpha
       beta
@@ -249,13 +252,20 @@
         # comparison.
         current = if formula
           if formula.head_only?
-            Version.new(formula.any_installed_version.version.commit)
-          else
-            T.must(formula.stable).version
+            formula_commit = formula.any_installed_version&.version&.commit
+            Version.new(formula_commit) if formula_commit
+          elsif (stable = formula.stable)
+            stable.version
           end
         else
           Version.new(formula_or_cask.version)
         end
+        unless current
+          raise Livecheck::Error, NO_CURRENT_VERSION_MSG unless json
+          next if quiet
+
+          next status_hash(formula_or_cask, "error", [NO_CURRENT_VERSION_MSG], full_name: use_full_name, verbose:)
+        end
 
         current_str = current.to_s
         current = LivecheckVersion.create(formula_or_cask, current)
@@ -289,7 +299,7 @@
                 verbose:,
               )
               if res_version_info.empty?
-                status_hash(resource, "error", ["Unable to get versions"], verbose:)
+                status_hash(resource, "error", [NO_VERSIONS_MSG], verbose:)
               else
                 res_version_info
               end
@@ -299,13 +309,12 @@
         end
 
         if latest.blank?
-          no_versions_msg = "Unable to get versions"
-          raise Livecheck::Error, no_versions_msg unless json
+          raise Livecheck::Error, NO_VERSIONS_MSG unless json
           next if quiet
 
           next version_info if version_info.is_a?(Hash) && version_info[:status] && version_info[:messages]
 
-          latest_info = status_hash(formula_or_cask, "error", [no_versions_msg], full_name: use_full_name,
+          latest_info = status_hash(formula_or_cask, "error", [NO_VERSIONS_MSG], full_name: use_full_name,
                                                                                  verbose:)
           if check_for_resources
             unless verbose
@@ -986,7 +995,7 @@
         res_current = T.must(resource.version)
         res_latest = Version.new(match_version_map.values.max_by { |v| LivecheckVersion.create(resource, v) })
 
-        return status_hash(resource, "error", ["Unable to get versions"], verbose:) if res_latest.blank?
+        return status_hash(resource, "error", [NO_VERSIONS_MSG], verbose:) if res_latest.blank?
 
         is_outdated = res_current < res_latest
         is_newer_than_upstream = res_current > res_latest