[RFC PATCH 0/6][GSoC] iterate dirs before or after their contents

Hello. Some time ago I worked on converting opendir/readdir calls to use dir-iterator [1], however this cleanup required to iterate directory paths after their contents. Matheus pointed me out to a previous patch series[2] that attempted to implement such functionality in dir-iterator. From it, I mainly used Michael's feedback and feature requests and tried to include it in my work.

My fork: https://github.com/kioplato/git/tree/dir-iterator
CI: https://github.com/kioplato/git/actions/runs/2141288008
There are some memleaks, I'll track them down in v2.

I aim to implement more functionality in dir-iterator, my goal being to simplify
the codebase by introducing an abstraction layer for iterating directories.
I would like to eventually simplify read_directory_recursive(). I wanted to
check in with you to make sure I'm heading in the right direction with what I've
implemented.
  * Are my tests overly exhaustive?
  * As of now we can't thoroughly test dir-iterator on directories with complex
  structure since readdir produce dirents with undefined order in a directory.
  I thought about introducing a tool for generating permutations with stable
  parts in test-lib. Is there a need to something like this for other tests?
  Or maybe should I sort each level iterated by dir-iterator inside
  test-dir-iterator before printing to stdout? In these patches I did enumerate
  the path permutations for some tests by hand, but that's not viable really.
  * We also don't test for deleted entries between dir_iterator_advance() calls.
  * Are my comments too much? Throughout git, .c files don't have many comments,
  should I remove mine as well? I think they provide better context when reading
  through the source code.

I do understand that it probably is too early to worry about most of these. However I wanted to communicate my thoughts and setup for the following versions.

While I wait for review, I'll implement/fix:
  * DIR_ITERATOR_RECURSE proposed here[3], but with finer control. Instead of a
  flag I'll introduce a new integer parameter in dir_iterator_begin(), which
  will specify the maximum iteration depth.
    * Supplying 0 will have the same behavior as DIR_ITERATOR_RECURSE i.e. it
    will iterate over the entries of the root directory.
    * Supplying -1 will iterate to maximum depth. This is the default right now.
  * DIR_ITERATOR_DIRS_ONLY proposed here[4]. Enabling this, dir-iterator will
  show only directories. Failing to enable DIR_ITERATOR_DIRS_BEFORE and/or
  DIR_ITERATOR_DIRS_AFTER will result in dir_iterator_begin() returning NULL.
  Is this a good way to encode "show only directories" in the flags?

I'll include them along with feedback and suggestions from this version in the next one.

I didn't refactor entry.c to use dir-iterator. It's a good first issue for someone else to become introduced to the community. I applied my patch[1] and it does not pass t/, as it used to, because of 15th test in t1092. Should I work on entry.c in my next version or leave it alone for a newcomer?

This serves as my microproject for GSoC. Could my future work on dir-iterator and cleanup of read_directory_recursive() and other customers of dir-iterator become a seperate GSoC project I could undertake?

[1]: https://public-inbox.org/git/20191208180439.19018-1-otalpster@gmail.com/ [2]: https://public-inbox.org/git/1493226219-33423-1-git-send-email-bnmvco@gmail.com/ [3]: https://public-inbox.org/git/CACsJy8DBa-oH3i+5P=iVr9NhJwsicZ43DO89WmvpYEQu90RrMw@mail.gmail.com/ [4]: https://public-inbox.org/git/xmqqmvc265hk.fsf@gitster.mtv.corp.google.com/

Plato Kiorpelidis (6):
  t0066: improve readablity of dir-iterator tests
  t0066: better test coverage for dir-iterator
  dir-iterator: refactor dir_iterator_advance()
  dir-iterator: iterate dirs before or after their contents
  t0066: remove redundant tests
  test-dir-iterator: handle EACCES errno by dir-iterator

 builtin/clone.c              |    4 +-
 dir-iterator.c               |  302 ++++++---
 dir-iterator.h               |   34 +-
 refs/files-backend.c         |    2 +-
 t/helper/test-dir-iterator.c |   23 +-
 t/t0066-dir-iterator.sh      | 1202 +++++++++++++++++++++++++++++++---
 6 files changed, 1371 insertions(+), 196 deletions(-)