Sort remaining completion candidates in RegexpCompletor (#1230)

#379 sorted local variables and string method candidates, but
receiver.method completion (the most common case), symbols, global
variables and absolute constants were still returned in method table
order, which looks random in the completion dialog. Sort them too.
Candidates starting with an underscore go last, so that completing
`u.` does not begin with __id__, __send__ and other internals.

Author: kryzhovnik

lib/irb/completion.rb

@@ -302,7 +302,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
           rescue EncodingError
             # ignore
           end
-          candidates.grep(/^#{Regexp.quote(sym)}/)
+          candidates.grep(/^#{Regexp.quote(sym)}/).sort
         end
       when /^::([A-Z][^:\.\(\)]*)$/
         # Absolute Constant or class methods
@@ -313,7 +313,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
         if doc_namespace
           candidates.find { |i| i == receiver }
         else
-          candidates.grep(/^#{Regexp.quote(receiver)}/).collect{|e| "::" + e}
+          candidates.grep(/^#{Regexp.quote(receiver)}/).sort.collect{|e| "::" + e}
         end
 
       when /^([A-Z].*)::([^:.]*)$/
@@ -331,7 +331,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
             candidates = []
           end
 
-          select_message(receiver, message, candidates.sort, "::")
+          select_message(receiver, message, candidates, "::")
         end
 
       when /^(:[^:.]+)(\.|::)([^.]*)$/
@@ -400,7 +400,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
         if doc_namespace
           all_gvars.find{ |i| i == gvar }
         else
-          all_gvars.grep(Regexp.new(Regexp.quote(gvar)))
+          all_gvars.grep(Regexp.new(Regexp.quote(gvar))).sort
         end
 
       when /^([^.:"].*)(\.|::)([^.]*)$/
@@ -452,7 +452,7 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
         if doc_namespace
           "String.#{candidates.find{ |i| i == message }}"
         else
-          select_message(receiver, message, candidates.sort)
+          select_message(receiver, message, candidates)
         end
       when /^\s*$/
         # empty input
@@ -491,7 +491,11 @@ def retrieve_completion_data(input, bind:, doc_namespace:)
     Operators = %w[% & * ** + - / < << <= <=> == === =~ > >= >> [] []= ^ ! != !~]
 
     def select_message(receiver, message, candidates, sep = ".")
-      candidates.grep(/^#{Regexp.quote(message)}/).collect do |e|
+      sorted_candidates = candidates.grep(/^#{Regexp.quote(message)}/).sort_by do |e|
+        # Alphabetical order, but internal methods (leading underscore) last
+        [e.start_with?('_') ? 1 : 0, e]
+      end
+      sorted_candidates.collect do |e|
         case e
         when /^[a-zA-Z_]/
           receiver + sep + e

test/irb/test_completion.rb

@@ -95,6 +95,17 @@ def test_complete_class
         assert_include(completion_candidates("String.ne", binding), "String.new")
         assert_equal("String.new", doc_namespace("String.new", binding))
       end
+
+      def test_complete_methods_are_sorted
+        u = ''
+        u.clear
+
+        candidates = completion_candidates("u.", binding)
+        assert_include(candidates, "u.__id__")
+        underscore, regular = candidates.partition { |c| c.start_with?("u._") }
+        # Alphabetical order, internal methods (leading underscore) last
+        assert_equal(regular.sort + underscore.sort, candidates)
+      end
     end
 
     class RequireComepletionTest < CompletionTest
@@ -215,6 +226,11 @@ def test_complete_sort_variables
         candidates = completion_candidates("xz", binding)
         assert_equal(%w[xzy xzy2 xzy_1], candidates)
       end
+
+      def test_complete_sort_global_variables
+        candidates = completion_candidates("$std", binding)
+        assert_equal(%w[$stderr $stdin $stdout], candidates)
+      end
     end
 
     class ConstantCompletionTest < CompletionTest
@@ -255,6 +271,18 @@ def test_complete_symbol
       assert_empty(completion_candidates(":", binding))
     end
 
+    def test_complete_symbols_are_sorted
+      candidates = completion_candidates(":a", binding)
+      refute_empty(candidates)
+      assert_equal(candidates.sort, candidates)
+    end
+
+    def test_complete_absolute_constants_are_sorted
+      candidates = completion_candidates("::S", binding)
+      refute_empty(candidates)
+      assert_equal(candidates.sort, candidates)
+    end
+
     def test_complete_invalid_three_colons
       assert_empty(completion_candidates(":::A", binding))
       assert_empty(completion_candidates(":::", binding))