[Fix #1260] Fix performance regression caused by Rails/UnknownEnv
on rails 7.1
#1262
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After upgrading to Rails 7.1 we noticed a significant slowdown of RuboCop (52s -> 3m 52s).
We found that the cache file path for certain files was changing throughout the RuboCop execution, resulting in cache misses. One of the components of the cache file path is the cop config.
When diffing the cop config throughout RuboCops execution we find that "Rails/UnknownEnv"."Environments" is changing:
When Rails/UnknownEnv runs as part of the warm_cache step in RuboCop it mutates the config, which subsequently modifies the file checksums. When RuboCop runs inspect_files it results in cache misses because the cop config is no longer the same.
The code causing the issue:
In this case
cop_config['Environments']
is mutated whenenvironments << 'local'
runs.Before submitting the PR make sure the following are checked:
[Fix #issue-number]
(if the related issue exists).master
(if not - rebase it).bundle exec rake default
. It executes all tests and runs RuboCop on its own code.{change_type}_{change_description}.md
if the new code introduces user-observable changes. See changelog entry format for details.