GSoC Student Guidance and Project Ideas for 2019

Please see also our SummerOfCode/2019 page, which contains additional information for GSoC for this year.

1. About Mercurial

• What is Mercurial? Mercurial is a free, distributed source control management tool. It efficiently handles projects of any size and offers an easy and intuitive interface.

• Why is it interesting? Besides the extremely good reasons just above, Mercurial is also interesting for many other reasons, including: a great extension system, excellent backwards compatibility, excellent documentation, ... Specifically for students, it's interesting because it offers a range of topics to work on from low-level speed optimizations all the way up to a web interface.

• Who uses it? Mercurial is used by individuals, organizations and companies all over the world. The same goes for contributors: in the open source community, a well-known organization using Mercurial is the Mozilla project, but companies like Facebook, Google and many others also contribute to Mercurial.

• What language is it written in? Mercurial is mostly written in Python. We rewrite some parts that are very performance-sensitive in C and Rust.

2. Contacting the Mercurial developers

The following channels are used by default for communication. Please use them to introduce yourself!

• IRC: many developers chat and discuss planned changes to Mercurial here. Keep in mind that most developers are in US timezones, so it might take quite a bit of time (hours) to get a response outside of those timezones!

• The developer mailing list: this list is mostly used to submit patches and discuss them.

If you don't have a persistent internet connection, it is advised to email the developer list instead of IRC because it may take time to get a reply.

3. Getting started/Candidate checklist

All candidates should do the following before completing their application:

1. Check the SummerOfCode/Ideas2019 page

2. Subscribe to this page to get email when it changes

3. Introduce yourself on IRC

4. Introduce yourself on the mailing list

5. Read the ContributingChanges pages.

6. Look at the easy bugs list and contribute a patch. Feel free to ask questions on IRC or the mailing list while getting started!

7. Follow the steps to apply: check the application checklist and submit your application.

4. Things we look for in a candidate

• Demonstrates understanding of our tools, procedures, and source code by successfully submitting patches (see last step above)
• Participates in the community, especially via IRC
• Makes a commitment to work on GSoC full-time
• Gives an indication that she or he enjoys working with Mercurial enough to become a long-term contributor, after GSoC is over.

5. GSoC ideas

Here are some ideas of possible 2019 summer project ideas for Mercurial. Your own ideas are welcome. You may decide to work on these ideas or use them as a starting point for your own.

5.1. Example Project

• Project description: This is an example project. Please add a clear description with some details about the idea.

• Skills: Specific programming languages, domain-specific knowledge... For example: Python, network programming

• Difficulty level: Easy/Intermediate/Difficult

• Related reading/Links: Useful links to wiki pages, specific relevant mailing list discussions or patches, ...

• Further details: Additional detail about the idea

• Point of Contact: Who wrote this proposal and could answer question about it.

• Potential mentors: mentors likely to be involved with this project

5.3. Add functionality to store an unresolved merge-state

5.3.1. Project description

Merge conflicts are painful. How about having a functionality where we can store an unresolved merge state? This will help us in doing other tasks if required at the moment in the same repository and also get back to the same merge state and resume resolving conflicts.

This project involves developing a functionality where an unresolved state can be stored in some way and can be restored in future. The commands which perform merge between two revisions like merge, graft, rebase, histedit, shelve can result in merge conflicts. For commands like rebase, histedit, we might need to store their state files too.

Also, pijul version control already does that. It let's you commit conflicts as conflicts and then you can solve them later or have someone else do that.

To get to this stage, following are the tasks which needs to be done in order:

• develop a plan with breaking the whole task into smaller sub-tasks. This may also involve investigating how pijul does that
• think of an UI which can be used to store and restore merge-states
• Analyze what are the things which need to be stored and develop storage layer for that

• Implement the support for hg merge command

• Implement support for multi-step commands like rebase, histedit
• think about support for exchanging such data
• Add documentation and tests for every code you write!

Although this will take good amount of time but in-case this turns out be easier, other small tasks related to merge state and related things can be added.

5.3.2. Project properties

• Skills: Python

• Difficulty level: Intermediate

• Point of Contact: pulkitg on IRC

• Potential mentors: Pulkit Goyal, Sushil Khanchi, Sangeet Kumar Mishra

5.4. Implement continue and abort command

5.4.1. Project description

Commands like rebase, histedit, shelve etc. can lead to a conflicted state and requires user intervention. The user need to remember the original operation to continue or abort the operation. This project is about implementing generic hg continue and hg abort commands.

The implementation should have functionality for extensions to plug in their logic. For example, commands introduced by out of core extensions can use hg continue and hg abort functionality.

To get to this stage, following are the tasks which needs to be done in order:

• understand how existing --continue and --abort flags work

• plan how we can implement hg continue and hg abort

• implement the commands supporting basic commands like graft
• implement support for commands provided by in-core extension like rebase, histedit, shelve
• make sure implementation can be used in extensions and if possible implement support in evolve extension

Although this will take good amount of time but in-case this turns out be easier, other tasks like implementing hg update --abort and hg stop should we worked on.

5.4.2. Project properties

• Skills: Python

• Difficulty level: Intermediate

• Point of Contact: pulkitg on IRC

• Potential mentors: Pulkit Goyal, Sangeet Kumar Mishra, Sushil Khanchi

6. Other ideas?

There are more things on WeShouldDoThat which we will like someone to work on. You can pick an idea from there too.

Come talk to us on IRC.

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