### Summary `rules:changes` seem to be impacted by [built-in limits for merge requests and diffs](https://docs.gitlab.com/ee/administration/diff_limits.html). For example consider a CI/CD config with two jobs, each defining `rules:changes` using a wildcard path for different directories. When the number of file changes for a merge request exceeds the defined diffs limit changes for the second directory are not visible in the changes tab. The job which defines `rules:changes` targeting the missing directory for the merge request changes does not run for the merge request pipeline.. This is unexpected, no documentation. ### Steps to reproduce 1. Create a project on GitLab.com 2. Clone the project 3. Run the below script to create approx 3000 files in folders `1` and `2` ``` #!/bin/bash for n in {1..2}; do mkdir $n for i in {1..3001}; do echo 'test' >> $n/$i.txt done done ``` 4. Add, commit and push the files to Gitlab.com 5. Add the CI/CD config below to the project ``` changes_in_1: extends: - .changes_in_1:build_rules script: - echo "changes_in_1" changes_in_2: extends: - .changes_in_2:build_rules script: - echo "changes_in_2" .changes_in_1:build_rules: rules: - if: changes: - 'config/**/*' - '1/**/*' .changes_in_2:build_rules: rules: - if: changes: - 'config/**/*' - '2/**/*' ``` 6. Create and switch new feature branch 7. Run the bash script again to modify all in folders `1` and `2` 8. Add, commit and push the branch to Gitlab.com 9. Create the merge request on GitLab.com 10. Inspect the created merge request pipeline and note that only one job runs ### Proposal The [FindChangedPaths](https://gitlab.com/gitlab-org/gitaly/-/blob/686929072dce472eb062521cf63f0e1bda4d310f/internal/gitaly/service/diff/find_changed_paths.go#L40) Gitaly RPC can be used to get tree-level changes between a set of revisions in a repository and is not affected by diff limits. From what we can tell, this should fit the needed use-case for detecting changes and shouldn't require too much performance overhead. It sounds like the current approach uses the `CommitDiff` RPC, so using `FindChangedPaths` instead might improve performance. As there remains some uncertainty about the performance impact of this change, we should put it behind a feature flag to allow for a gradual rollout. ### Example Project ### What is the current _bug_ behavior? A job where the `rules:changes` keyword targets a directory that contains changed files is not running for the merge request pipeline. ### What is the expected _correct_ behavior? A job where the `rules:changes` keyword targets a directory that contains changed files should run for the merge request pipeline. ### Output of checks This bug happens on GitLab.com ### Possible fixes and implementation details. Use `FindChangesPaths` for `rules:changes`, more information in [this thread](https://gitlab.com/gitlab-org/gitlab/-/issues/433257#note_1722430360)