This change adds the preserve_mtime attribute to the copy_to_directory and copy_directory rules. When set the copied files will have their modified time set to the same value as the original source.

The motivation for adding this feature is that I was building a third party library from source using rules_foreign_cc and tried to use copy_to_directory to merge in a configuration header with the upstream source. Without this feature all of the modify times were reset and this caused the build to erroneously determine that generated files packaged with the source were out of date. With this preserve_mtime feature I was successfully able to build the third party library using the released version of these files.

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

The copy_directory and copy_to_directory rules now support preserving the original modification time of their sources.

Test plan

• Temporarily updated the two rules to use the version of the tools form the repository by uncommenting the development only tool sections.
• A a new test_preserve_mtime under e2e/smoke test was added that verifies that the modified times are the same in the destination as the source.
• The preserve_mtime = True attribute was temporally removed from the targets that are used by the test. It was verified the old behavior still occurred and the test failed with an appropriate error message.
• All existing tests under e2e were executed.