Pass section to the constructor

Library/Homebrew/cask/artifact/manpage.rb

@@ -5,26 +5,26 @@ require "cask/artifact/symlinked"
 module Cask
   module Artifact
     class Manpage < Symlinked
+      attr_reader :section
+
       def self.from_args(cask, source)
-        section = source.split(".").last
+        section = source.to_s[/\.([1-8]|n|l)$/, 1]
 
-        raise CaskInvalidError, "section should be a positive number" unless section.to_i.positive?
+        raise CaskInvalidError, "'#{source}' is not a valid man page name" unless section
 
-        new(cask, source)
+        new(cask, source, section)
       end
 
-      def initialize(cask, source)
-        super
+      def initialize(cask, source, section)
+        @section = section
+
+        super(cask, source)
       end
 
       def resolve_target(_target)
         config.manpagedir.join("man#{section}", target_name)
       end
 
-      def section
-        @source.extname.downcase[1..-1].to_s.to_i
-      end
-
       def target_name
         "#{@source.basename(@source.extname)}.#{section}"
       end

Library/Homebrew/test/cask/artifact/manpage_spec.rb

@@ -8,7 +8,7 @@ describe Cask::Artifact::Manpage, :cask do
     let(:cask_token) { "invalid/invalid-manpage-no-section" }
 
     it "fails to load a cask without section" do
-      expect { cask }.to raise_error(Cask::CaskInvalidError, /section should be a positive number/)
+      expect { cask }.to raise_error(Cask::CaskInvalidError, /is not a valid man page name/)
     end
   end