GSoC Student Guidance and Project Ideas for 2019

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

Contents

About Mercurial
Contacting the Mercurial developers
Getting started/Candidate checklist
Things we look for in a candidate
GSoC ideas
Other ideas?

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.

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:

Check the SummerOfCode/Ideas2018 page
Subscribe to this page to get email when it changes
Introduce yourself on IRC
Introduce yourself on the mailing list
Read the ContributingChanges pages.
Look at the easy bugs list and contribute a patch. Feel free to ask questions on IRC or the mailing list while getting started!
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

5.2. Improve commit graph in hgweb

5.2.1. Project description

Used Github, Gitlab, Bitbucket or other code hosting platforms and got interested how things are working there. Well this project is for you then!

hgweb is the web UI that comes together with Mercurial and so is readily available to every user, it somewhat lags behind in presentation. You can see an example of the current hgweb interface at the Mercurial's main repo. One can run their own hgweb server using hg serve command. As you can see, in the today's world where we nice styled components using react, hgweb looks like a 2010 website.

This project focuses on improving graph rendering in hgweb, because seeing the DAG can be very useful and because there's plenty of ideas on how to improve it. We could make it faster and smarter, show more things, and look nicer. Here are some ideas, but not all of them are required, and more ideas can be added in the process if everyone agrees on them.

Think up a good (extensible, self-descriptive) format for new graph data to put into JSON and implement it server-side
Display special edges, such as source-destination of a graft and obsolescence relations. More info about obsolescence relations can be found here
Make graph more space-efficient (visually) and easier to understand by using different colors (there is color variation for different branches, but the algorithm can be improved and color variation can potentially be added to nodes too)
Show faded-out edge(s) on screen top and bottom when there are more changesets available, to imply that the current view doesn't include all of the changesets
Solve issue4020 either by splitting graph into multiple visual elements (<canvas> or <svg>), by sliding viewport or by other means
Maybe use SVG instead of <canvas>, and add tooltips to some elements (e.g. graph nodes of unstable commits)
Discussing new ideas on how source control information can be displayed on a web page

We can borrow more ideas from existing code hosting platforms such as Github, Gitlab, Bitbucket, Kiln, RhodeCode etc.

5.2.2. Project properties

Skills: Python (server-side), JavaScript (client-side)
Difficulty level: Intermediate (but can become more difficult if you can take up some of the more complicated subtasks)
Related reading/Links: https://bz.mercurial-scm.org/show_bug.cgi?id=4020 https://bz.mercurial-scm.org/show_bug.cgi?id=2570 (not limited to these)
Point of Contact: TBD
Potential mentors: TBD

5.3. Curses UI for annotate and other commands

5.3.1. Project description

How cool are the programs which interact with you, right?

In mercurial, we have an interactive curses interface which uses python curses module. Right now curses UI can be to select chunks to commit, revert, shelve and also do a histedit. This project is about using curses UI in more places like annotate.

Annotate is a command which shows history of each line in a file. Think of an UI, where you go to a line, hit back button, and go back to old version of that line. Select a commit and go back to the state of the file at that commit. Sounds very interesting right?

To get to this stage, we need to do the following:

understand how python curses module works and how that is used in existing commands
design a UI for annotate command which can be implemented using curses
implement required API's in core mercurial to which curses API's can talk
implement the curses interface for the command and add tests!

Although this will take good amount of time but in-case this turns out be easier, the project will involve implementing curses UI for other commands.

5.3.2. Project properties

Skills: Python
Difficulty level: Intermediate
Related reading/Links: Python curses API
Point of Contact: pulkitg on IRC
Potential mentors: TBD

5.4. Add functionality to store an unresolved merge-state

5.4.1. 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.