Add spec for a complex Regexp with comments

* See #2412

Author: eregon

spec/ruby/language/regexp/grouping_spec.rb

@@ -32,4 +32,32 @@
      b   # there is no capture group on this line (not even here)
      $/x.match("ab").to_a.should == [ "ab", "a" ]
   end
+
+  it "does not consider # inside a character class as a comment" do
+    # From https://github.com/rubocop/rubocop/blob/39fcf1c568/lib/rubocop/cop/utils/format_string.rb#L18
+    regexp = /
+        % (?<type>%) # line comment
+      | % (?<flags>(?-mix:[ #0+-]|(?-mix:(\d+)\$))*) (?#group comment)
+        (?:
+          (?: (?-mix:(?<width>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:\.(?<precision>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:<(?<name>\w+)>)?
+            | (?-mix:(?<width>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:<(?<name>\w+)>) (?-mix:\.(?<precision>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))?
+            | (?-mix:<(?<name>\w+)>) (?<more_flags>(?-mix:[ #0+-]|(?-mix:(\d+)\$))*) (?-mix:(?<width>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:\.(?<precision>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))?
+          ) (?-mix:(?<type>[bBdiouxXeEfgGaAcps]))
+          | (?-mix:(?<width>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:\.(?<precision>(?-mix:\d+|(?-mix:\*(?-mix:(\d+)\$)?))))? (?-mix:\{(?<name>\w+)\})
+        )
+    /x
+    regexp.named_captures.should == {
+      "type" => [1, 13],
+      "flags" => [2],
+      "width" => [3, 6, 11, 14],
+      "precision" => [4, 8, 12, 15],
+      "name" => [5, 7, 9, 16],
+      "more_flags" => [10]
+    }
+    match = regexp.match("%6.3f")
+    match[:width].should == '6'
+    match[:precision].should == '3'
+    match[:type].should == 'f'
+    match.to_a.should == [ "%6.3f", nil, "", "6", "3"] + [nil] * 8 + ["f"] + [nil] * 3
+  end
 end