We hit this case as well, it seems like for us --use-alternative-excluding fixes it, but our case isn't very complex, we just try to exclude some potential nested derived data directories

included: [Modules, tools]
excluded:
  - tools/*/.build
  - tools/*/DerivedData
  - tools/ibmodulelint/tests/fixtures
  - tools/illustrationstrip/tests/fixtures
  - tools/new_feature

Interestingly based on inspecting file opens it looks like what's happening is that when we pass a file list like @/tmp/abc.txt with just ~200 files, for every file it appears that swiftlint is re-resolving all files under the matching globs, which in the case where I noticed it is ~10k files, so I guess swiftlint is attempting ~2 million file stats before even starting to lint. Maybe that isn't the only cause of the slowdown but in my case it results in ~7 minutes to lint these ~200 files, which with --use-alternative-excluding lint in ~1 second.

You can see most of the time is spent in NSFileManager

Our exclusion list is as follows, and we saw a 3s->150s increase in execution time

included: # paths to include during linting.
  - '*/Sources'
  - '*/Tests'
excluded: # paths to ignore during linting. Takes precedence over `included`.
  - '.build'
  - '.swiftpm'
  - 'Sources/GraphQLQueries'
  - '**/*.graphql.swift'

There doesn't seem to be a way to actually use the --use-alertnative-excluding flag when using SwiftLint as a SwiftPM plugin?

Could this "easily" be added to the configuration file?

With further testing, this performance impact is only seen when using globstar exclusion patterns.

If I instead list out the directories directly, SwiftLint execution drops down to the expected sub-second timing

I'm having same issue, so you solution is to change this

included: # paths to include during linting.
  - '*/Sources'
  - '*/Tests'
excluded: # paths to ignore during linting. Takes precedence over `included`.
  - '.build'
  - '.swiftpm'
  - 'Sources/GraphQLQueries'
  - 'folder/graphql.swift'

removing the ** from the path.
asking because I added few more folders to exclude and swift link plugin went from 1.6s to 23.7 seconds

In my case I've been avoiding the problem by making sure that these `.build' folders don't get generated (via some settings in the Swift VSCode extension), but that's not ideal.

As a general rule one should avoid having the include and exclude patterns match too many files. They should be rather specific to avoid performance issues. I hope this restriction can be mitigated by #5157.