hashdir

A CLI to calculate a single hash for the contents of a directory.

It uses the xxh3 algorithm to calculate the hash of each file and it respects .gitignore files, thanks to the ignore crate.

hashdir dir

Is roughly equivalent to this bash one-liner, minus the .gitignore support:

find dir -type f -print0 | sort -z | xargs -0 sha1sum | sha1sum

Why would you want to do this?

It can be useful to cache expensive operations when code hasn't changed. For example, you could use this to cache test runs in a monorepo when other parts of the codebase change.

Imagine you have a situation like the following:

gitGraph
    commit
    commit
    branch feat/a
    branch feat/b
    checkout feat/a
    commit
    checkout feat/b
    commit
    checkout main
    merge feat/a
    checkout feat/b
    merge main
    checkout main
    merge feat/b
    commit
    commit

You have a main branch and two feature branches feat/a and feat/b. feat/a and feat/b operate on different parts of the codebase, so they can't possibly generate conflicts.

You merge feat/a into main and then rebase or merge feat/b on top of main. At this point your CI will run again, even though the code in feat/b hasn't changed.

If you had a test report that matches the hash of the code in feat/b you could skip running the tests again if the hash hasn't changed.

In a rudimentary way, this is similar to what nx and turbo do in the JavaScript ecosystem.

TommasoAmici/hashdir

hashdir

Why would you want to do this?