cpg314 / mtime-rewind

Rewind the mtime of files whose mtime advanced since the last execution without a content change.

mtime-rewind

Rewind the mtime attribute of files whose modification advanced since the last execution without a content change.

This is useful to avoid unnecessary cache invalidations in systems using mtime to detect changes, for example Rust's cargo (see this issue).

More generally, see the mtime comparison considered harmful blog post.

Usage

$ mtime-rewind
Rewind the mtime of files whose mtime advanced since the last execution without a content change

Usage: mtime-rewind [OPTIONS] <ROOT>

Arguments:
  <ROOT>

Options:
      --dry   Do not edit only mtime, only list the changes that would be made
  -h, --help  Print help

• The first execution will store hashes and modification times of files in a .hashprint file at the root. Hidden files and cache directories are ignored.
• Subsequent executions will rewind files that have not changed to the previous modification time, and update the modification times of other files if necessary.

Typically, mtime-rewind can be executed as the first step of a CI build.

Example

$ mtime-rewind ~/project
[INFO mtime_rewind] Computing hashes...
[INFO mtime_rewind] Computed hashes for 9 files
[INFO mtime_rewind] Writing hashes for the first time...
[INFO mtime_rewind] Wrote "/root/project/.hashprint"
[INFO mtime_rewind] Done
$ touch src/main.rs
[INFO mtime_rewind] Computing hashes...
[INFO mtime_rewind] Computed hashes for 9 files
[INFO mtime_rewind] Restoring modification times for unchanged files...
[INFO mtime_rewind] Loading cached state...
[INFO mtime_rewind] Loaded hashes for 9 files
[INFO mtime_rewind] Rewinding "/root/project/src/main.rs" from SystemTime { tv_sec: 1693727396, tv_nsec: 146042169 } to SystemTime { tv_sec: 1693727019, tv_nsec: 668108072 } as its contents did not change
[INFO mtime_rewind] 1 files rewinded
[INFO mtime_rewind] Saving the new state...
[INFO mtime_rewind] Wrote "/root/project/.hashprint"
[INFO mtime_rewind] Done