Support shortening lambda notation

Author: aycabta

lib/irb/ruby-lex.rb

@@ -398,7 +398,7 @@ def check_newline_depth_difference
         next
       end
       case t[1]
-      when :on_lbracket, :on_lbrace, :on_lparen
+      when :on_lbracket, :on_lbrace, :on_lparen, :on_tlambeg
         depth_difference += 1
         open_brace_on_line += 1
       when :on_rbracket, :on_rbrace, :on_rparen
@@ -481,7 +481,7 @@ def check_corresponding_token_depth
         next
       end
       case t[1]
-      when :on_lbracket, :on_lbrace, :on_lparen
+      when :on_lbracket, :on_lbrace, :on_lparen, :on_tlambeg
         spaces_of_nest.push(spaces_at_line_head + open_brace_on_line * 2)
         open_brace_on_line += 1
       when :on_rbracket, :on_rbrace, :on_rparen

test/irb/test_ruby_lex.rb

@@ -234,5 +234,21 @@ def test_oneliner_method_definition
         assert_indenting(lines, row.new_line_spaces, true)
       end
     end
+
+    def test_tlambda
+      input_with_correct_indents = [
+        Row.new(%q(if true), nil, 2),
+        Row.new(%q(  -> {), nil, 4),
+        Row.new(%q(  }), 2, 2),
+        Row.new(%q(end), 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+      end
+    end
   end
 end