The CODEOWNERS file in a GitHub repository is used to define individuals or teams that are responsible for specific parts of the codebase. When changes are made to files or directories that match the patterns specified in the CODEOWNERS file, GitHub automatically requests reviews from the listed code owners.

Setting Reviewers Automatically:

Option D is correct because the primary purpose of a CODEOWNERS file is to automatically set reviewers for pull requests that affect the specified files or directories. This ensures that the appropriate team members are notified and review the changes before they are merged.

Incorrect Options:

Option A is incorrect because the CODEOWNERS file does not restrict who can edit specific files; it only influences who is required to review changes.

Option B is partially related but not fully accurate because while CODEOWNERS does require certain reviews, it does not mandate peer review for all code changes.

Option C is incorrect because the CODEOWNERS file does not define access permissions for the repository; it deals with code review processes.