Add an included_files method to base hook

In the minitest pre-push hook, we don't want to use `applicable_files`
but run the whole suite instead. However, we do want to allow
expliciting an `include` pattern in the configuration. Extracting an
`included_files` method so it can be reused in the hook seemed the
easiest solution.

This commit includes some minor refactorings.

Author: David Rodríguez

lib/overcommit/hook/base.rb

@@ -17,7 +17,7 @@ def to_s
   class Base # rubocop:disable Metrics/ClassLength
     extend Forwardable
 
-    def_delegators :@context, :modified_files
+    def_delegators :@context, :all_files, :modified_files
     attr_reader :config
 
     # @param config [Overcommit::Configuration]
@@ -155,11 +155,21 @@ def flags
     # Gets a list of staged files that apply to this hook based on its
     # configured `include` and `exclude` lists.
     def applicable_files
-      @applicable_files ||= modified_files.select { |file| applicable_file?(file) }.sort
+      @applicable_files ||= select_applicable(modified_files)
+    end
+
+    # Gets a list of all files that apply to this hook based on its
+    # configured `include` and `exclude` lists.
+    def included_files
+      @included_files ||= select_applicable(all_files)
     end
 
     private
 
+    def select_applicable(list)
+      list.select { |file| applicable_file?(file) }.sort
+    end
+
     def applicable_file?(file)
       includes = Array(@config['include']).flatten.map do |glob|
         Overcommit::Utils.convert_glob_to_absolute(glob)

lib/overcommit/hook_context/base.rb

@@ -79,6 +79,13 @@ def modified_files
       []
     end
 
+    # Returns the full list of files tracked by git
+    #
+    # @return [Array<String>]
+    def all_files
+      Overcommit::GitRepo.all_files
+    end
+
     # Returns the contents of the entire standard input stream that were passed
     # to the hook.
     #

lib/overcommit/hook_context/run_all.rb

@@ -7,7 +7,7 @@ module Overcommit::HookContext
   # which is useful for automated CI scripts.
   class RunAll < Base
     def modified_files
-      @modified_files ||= Overcommit::GitRepo.all_files
+      @modified_files ||= all_files
     end
 
     # Returns all lines in the file since in this context the entire repo is