SoC-2019-Ideas.md

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This is the idea page for Summer of Code 2019 for Git.

About applying for SoC with the Git project

Please read this section completely before reading the idea list below.

It is required that students who want to apply to the Git project for the Summer of Code 2019 complete a tiny, code-related "microproject" as part of their application. Please refer to our guidelines and suggestions for microprojects for more information. Completing a microproject is not only an important way for us to get experience with applicants, but it will also help applicants become familiar with Git's development and submission process.

A complete GSoC application should include a presentation of yourself (include any argument that may convince mentors that you are able to complete the project) and detailed explanations about your project. Ideas below are just ... ideas! The list is not exhaustive, and more importantly each idea only includes a summary of what is to be done. An application must include detailed plans on the design, timeline ... A typical application takes several pages. You should already have read the GSoC Student Guide by now, but re-read it if needed.

Also, working in Git project is not only about writing your own patches. Constructively critiquing design and implementation of patches by other people is also an important skill you need to learn in order to effectively collaborate with others. So, if you have time and inclination, it would be beneficial to read and understand other applicants' patches (or any other patch submitted to the mailing-list), think if you agree that the problem they are trying to solve is worth solving, the approach they are taking is the best way (or if you think of a better way to solve it), etc., and respond to their patches with the result of your thinking as a review.

Please, include link(s) to the mailing-list discussion(s) related to your microproject in your application (e.g. linking to public-inbox). If you participate in the review of other patches, then you may also include links to discussions that would support your application.

Students must send drafts of their proposal on the mailing-list before submitting it officially to GSoC to get feedback from the community. They are strongly encouraged to publish a draft on the official GSoC website and post it to the mailing list for discussion.

Getting your proposal right can follow the same process as usual patch submission for Git, as described in the microprojects page and in Documentation/SubmittingPatches in Git's source code. It is also expected that you will send several versions of your draft, responding to comments on the list. Please plan to send the first draft early enough so that a number of reviews and improvements cycles can happen.

If you are not sure about your proposal, you can discuss that in the same email where you introduce yourself or in separate emails. Please use "[GSoC]" at the beginning of such emails.

In summary, all applicants must (not necessarily in this order):

• Complete a microproject.

• Write a detailed application explaining their project.

• Discuss their project by posting drafts of their application on the mailing-list long before the deadline.

In your application, and in the discussions related to projects you are interested in, it is a good idea to:

• Include link(s) to the mailing-list discussion(s) related to the project you chose in your application or you are interested in, for example previous discussions or patch series about the topic. There might be interesting discussions about the topics that are several year old. It is also a good idea to summarize them.

• Include link(s) to the mailing-list discussion(s) related to the previous drafts of your application itself.

• Include link(s) to the mailing-list discussion(s) related to your microproject. If your microproject patches have been merged, please give the merge commits. Otherwise give their branch names and current status in the last "What's cooking in git.git" email from Junio.

• Include what is suggested in the GSoC Student Guide

(public-inbox can be used for searching the mailing list and linking to previous discussions.)

Note about the number of slots

In 2019, the Git organization has very limited mentoring capacity. These days we usually accept between 0 and 3 students per year.

Summer of code main project ideas

Students: Please consider these ideas as starting points for generating proposals. We are also more than happy to receive proposals for other ideas related to Git. Read the note below about refactoring projects versus projects that implement new features though.

Unify ref-filter formats with other --pretty formats

• Language: C, shell (bash)
• Difficulty: medium
• Possible mentors: Christian Couder, Olga Telezhnaya, Thomas Gummerer

Git has an old problem of duplicated implementations of some logic. For example, Git had at least 4 different implementations to format command output for different commands. Our previous GSoC students and Outreachy interns unified some of the formatting logic into ref-filter and got rid of similar logic in some command specific files. Current task is to continue this work and reuse ref-filter formatting logic in pretty.

See discussion in:

https://public-inbox.org/git/[email protected]/T/#u

git log --oneline improvements

• Language: C, shell (bash)
• Difficulty: medium
• Possible mentors: Christian Couder, Thomas Gummerer

A number of Git commands, like git log, can show commit information in a configurable way using "pretty" formats. Such formats though don't yet support some features that users would like, for example to display a log like the following:

  b9df16a4c (HEAD -> master)
            pathspec: don't error out on all-exclusionary pathspec patterns
  91a491f05 pathspec magic: add '^' as alias for '!'
  c8e05fd6d ls-remote: add "--diff" option to show only refs that differ
  20769079d (tag: v2.12.0-rc2, origin/master, origin/HEAD)
            Git 2.12-rc2
  076c05393 Hopefully the final batch of mini-topics before the final

See discussions in:

https://public-inbox.org/git/[email protected]/T/#t http://public-inbox.org/git/CA+55aFwT2HUBzZO8Gpt9tHoJtdRxv9oe3TDoSH5jcEOixRNBXg@mail.gmail.com/

Convert scripts to builtins

• Language: C, shell (bash), possibly Perl
• Difficulty: medium
• Possible mentors: Christian Couder, Thomas Gummerer

A few components of Git are still in the form of shell and sometimes Perl scripts. This causes problems in production code – in particular on multiple platforms, e.g. Windows (think: POSIX-to-Windows path conversion issues).

The idea of this project is to dive into the Git source code and convert a couple of shell and/or Perl scripts into portable and performant C code, making it a so-called "built-in".

(Un)fortunately, the important and easy to port scripts like git-pull.sh are already ported by now. It should still be possible to start with something small by porting portions of existing shell-scripts to C using a C helper inside the existing shell-script.

It will be an important part of the project to discuss and find the most interesting scripts or parts of scripts to be ported.

Improve consistency of sequencer commands

• Language: C, shell (bash)
• Difficulty: medium
• Possible mentors: Elijah Newren, Christian Couder, Thomas Gummerer

This would consist in taking care of the following issues:

• The suggestion to fix an interrupted rebase-i or cherry-pick due to a commit that became empty via git reset HEAD (in builtin/commit.c) instead of git rebase --skip or git cherry-pick --skip ranges from annoying to confusing. (Especially since other interrupted am's and rebases both point to am/rebase --skip.). Note that git cherry-pick --skip is not yet implemented, so that would have to be added first.

• There are a handful of flags that am-based rebases support that are not available to interactive/merge-based rebases; it'd be nice to implement them for the interactive machinery. (There are also numerous flags that only the interactive machinery supports that are unavailable to am-based rebases, but we don't care; we want to deprecate am-based rebases.)

  • --ignore-whitespace (transliterate to -Xignore-space-change?)
  • --whitespace=...
  • --committer-date-is-author-date/--ignore-date
  • -C4

• [There's also some empty handling (from "Behavioral Differences" in Documentation/git-rebase.txt) that would be nice to address, though that might be contentious and we might try to tackle that piece before GSoC gets rolling...]

• Bonus: Make a flag to allow rebase to rewrite commit messages that refer to older commits that were also rebased. (i.e. if rebasing commits A and B, and commit B says This reverts commit <sha-of-A>, then rewritten B's commit message should say This reverts commit <sha-of-rewritten-A>.) Do this for both sha1sums and sha1sum abbreviations in commit messages.

git revert --drop and git commit --reword

• Language: C, shell (bash)
• Difficulty: medium
• Possible mentors: Thomas Gummerer

The interactive rebase already supports the special oneline prefixes fixup! and squash! in the --autosquash mode; these commits will be reordered in the todo list and their pick commands adjusted accordingly.

These commits can be crafted conveniently via the --fixup and --squash options of git commit.

The idea of this project is to add two more actions, drop! and reword!:

• The drop! action (for convenience, git revert --drop <commit>) would not only revert the commit, but a subsequent git rebase -i --autosquash would reorder the drop! commit directly after the matching commit, then change the matching commit's pick to drop and comment out the drop! one.

• The reword! action (for convenience, git commit --reword <commit>) would let the user edit the commit message of the referenced commit, and add an "empty" commit (i.e. a commit that does not modify any files) with that commit message, prefixed with the reword! oneline. The next git rebase -i --autosquash would then not only reorder that commit after verifying that it is indeed an empty commit, it would then also replace the pick command with an appropriate new command (say, by extending the squash command to accept a --reword option).

This project will need to begin by implementing test cases to define the expected outcome, and then implement the actual functionality.

Teach git stash to handle unmerged index entries

• Language: C, shell (bash)
• Difficulty: medium
• Possible mentors: Thomas Gummerer

When the index is unmerged, git stash refuses to do anything. That is unnecessary, though, as it could easily craft e.g. an octopus merge of the various stages. A subsequent git stash apply can detect that octopus and re-generate the unmerged index.

See also the discussion in this Git mailing list thread.

Note about refactoring projects versus projects that implement new features

Over the years we have been favoring refactoring projects over possibly more interesting projects that implement new features. Refactoring projects are usually easier to do step by step, and to get code merged step by step which is encouraging.

In general refactoring projects are worthwhile to do even if the project is not finished at the end of the GSoC and even if the student stops contributing after that. In those cases it is often a good idea to later finish the refactoring either by ourselves or by proposing it to another GSoC student or Outreachy intern. This way the work of both students and mentors is not likely to be wasted.

With a project that implements a feature, there is a risk, if it's too complex or too difficult, that the feature will not be finished and that nothing, or nearly nothing, will have been merged during the GSoC. There is also the risk that another way to implement the feature will appear later in the GSoC and all, or nearly all, the work of the student and mentors will have been mostly wasted. It could also appear that the use cases the feature was envisioned to be used in, are better addressed by other improvements or a different workflow.

Another potential issue is that a new feature might be prone to naming or user interface discussions which could last for a long time or could not result in clear decisions.

Therefore we think that we should be very careful before proposing to a student, or accepting, a project that implements a new feature. People suggesting such a project should at least carefully consider the above potential issues and see if they can be mitigated before the project is submitted.

As suggested by Google we emphasize that a student proposing something original must engage with the community strongly before and during the application period to get feedback and guidance to improve the proposal and avoid the above potential issues.