Performance issues with 1.31.0 (Layout/FirstHashElementIndentation and Layout/FirstArrayElementIndentation)

[seandilda]

After updating to 1.31.0, my editor started complaining about rubocop timeouts. Some testing has narrowed the issue to the recent changes in Layout/FirstHashElementIndentation and Layout/FirstArrayElementIndentation.

Here are some timings from running time rubocop --cache false testfile.rb on a file I'm currently working on.

rubocop version	Layout/FirstHashElementIndentation enabled	Layout/FirstArrayElementIndentation enabled	time
1.30.1	true	true	3.5s
1.31.0	true	true	9.3s
1.31.0	true	false	5.3s
1.31.0	false	true	7.8s
1.31.0	false	false	3.4s

---

Expected behavior

RuboCop 1.31.0 should run at the same speed as 1.30.1

Actual behavior

Version 1.31.0 is several times slower when Layout/FirstHashElementIndentation and/or Layout/FirstArrayElementIndentation is enabled

Steps to reproduce the problem

Run rubocop --cache false on a file using a large number of hashes and arrays.

RuboCop version

1.31.0 (using Parser 3.1.2.0, rubocop-ast 1.18.0, running on ruby 2.7.6 x86_64-linux)
  - rubocop-rails 2.15.1

[dvandersluis]

I'm curious if you get the same results now that 1.31.1 was released? Did #10750 help?

[seandilda]

Thanks for the heads up! I just checked with 1.31.1 and I'm still seeing 9 second runs on that file. :(

[dvandersluis]

Are you able to share the file or an anonymized version of it?

[seandilda]

I've created a test file to reproduce this issue at https://gist.github.com/seandilda/a5872778c19fd82624809d856f0b7435

With 1.31.1, and both cops enabled, it takes 4.5s
With 1.31.1 and both cops disabled, it takes 2.1s
With 1.30.1 and both cops enabled, it takes 2.1s

[j-miyake]

I guess a part of the logic for searching an offensive node is expensive. For a small file, that may not be a big deal, but for a large file.

rubocop/lib/rubocop/cop/mixin/multiline_element_indentation.rb

Lines 70 to 76 in 023e0ea

	def node_beginning_with(left_brace)
	processed_source.ast.each_descendant do |node|
	if node.loc.is_a?(Parser::Source::Map::Collection) && (node.loc.begin == left_brace)
	break node
	end
	end
	end