This page is primarily intended for developers of Mercurial.

Good Ideas for Enhancements

Ideas that the community has discussed and largely approved of, but no one has yet implemented. This is somewhat distinct from Plan pages, although the two lists may overlap.

Projects listed here may be a good starting point for new contributors wanting to take on a more significant contribution than fixing "easy" bugs, without having to take on an up-front design discussion.

1. hg shellprompt

hg shellprompt bash "{branch} {node|shortest}": emits string for eval in bash to efficiently produce the specified template. Opens the door to first-part native prompt helpers that don’t have to start a Python. Prior art in docker’s command line tools?

Notes from the 4.4sprint on this topic: is also worth looking into.

2. Make -S/--subrepos flags unnecessary

It has always been the intention to make commands like hg status, hg add, hg remove, etc. handle subrepos transparently. The way to go about that is outlined here; status of this work was being tracked on SubrepoWork.

3. Sensible merge diffs

Mercurial shows diffs against the first parent for all changesets, including merges, unless explicitly instructed to show the diff against the second parent. It would be better if we could show only the changes which were made to resolve conflicts. Unified diff by definition can only show the differences between a parent and a child revision, but both Git's merge diff and the now-unmaintained MergediffExtension extend this by adding a second column of +/- annotations on each line.

It's possible we could even do better, by showing only the changes that were made to resolve conflicts (something like a diff between the mechanical merge output and the actual committed code). This would save users from needing to learn to read an even more complicated format than unified diff.

4. .mailmap support

Git supports a .mailmap file that can be used to map author names and email addresses to new values. For more info, see

Mercurial could likely support mailmap files relatively easily. Implementing it at the templating layer to rewrite author fields would be relatively easy. Implementing it in revsets is also pretty reasonable. Wiring it in to the changeset level is a bit more complicated since that could influence e.g. history rewriting. It probably lives in the revset and templating layer.

Update April 5 2018: mailmap is available as a template function, see

(Note: This mapping is similar to 'hg churn' aliases file functionality.)

5. `hg bundle` remote server support

It should be possible to use hg bundle against a remote server. This would convert the arguments into a getbundle wire protocol call and stream the emitted bundle to a local file.

6. curses merge tool

We have a curses interface for interactive commit. We should add a curses interfaces for merge conflict resolution.

7. Interactive revset prompt

Allow users to type a revset and see the results in real time via a curses interface. Also warn them about unexpectedly slow revsets (like date(...)).

8. Dry-run everywhere

Add -n dry-run functionality to many commands. Ex: rebase and histedit could print the smartlog that would result if it ran.

Update May 18, 2018: Sushil Khanchi is working on this as part of his Google Summer of Code project.

9. Side-by-side diff/log rendering

Allow rendering side-by-side comparisons. I.e. vertical split diff views; side by side smartlog comparisons

10. Interactive blame explorer

Curses UI that allows exploring the blame of a file (i.e. going to a line, hitting left and going to the previous version of that line)

11. Move our wiki to better place or improve the current wiki style

mpm was in favor of having of better styled wikis and we should do that for various purposes.

12. Source Transforming Module Importer for Python 2.7

We use a custom Python module importer on Python 3 to ease porting efforts. See also

We should consider doing something similar for Python 2.7. We would build a custom module importer that recognizes the Python 3 token stream and normalizes it to a Python 2.7 compatible token stream. This would be similar to except the transformation would be performed at import time instead of require a pre-execution source code compilation step.

Having a module importer that recognizes the Python 3 token stream would allow our source code to use Python 3 features. Notable features include type annotations and yield from. We could also rewrite items() to iteritems(), perform other transformations that make sense to ease porting efforts.

This would likely require vendoring copies of Python 3's and from the standard library, as we'd need to use Python 3's tokenizer on Python 2.

A proof of concept for this exists at

13. Add support for writing hgrc files from command line

In Mercurial we uses a set of configuration files to control aspects of its behavior. It depends on the path of a config file how it would behave for e.g. Local configuration which is inside a particular repository <repo>/.hg/hgrc will apply config options in current repository only or Global configuration $HOME/.hgrc which apply it's config option in every hg commands in any repository. To get detailed information about all the Mercurial configuration files and their syntax run hg help config.

At present, if you want to update a config file you would have to edit the hgrc file manually. We should have such functionality where one can update/insert a config option in a particular config file just by running a command.

14. Scriptable Interactive Commit Interface

IDEs and other GUI tools should be buildable on top of such an interface. Ideally users could do any of:

Naturally, this should also work for other --interactive diff-selection commands (revert, shelve, amend, etc).

15. Co-author and helped by functionality for commits

Git has this nice way of having multiple authors for a commit or specify Helped by.

16. See Also

CategoryDeveloper CategoryNewFeatures

WeShouldDoThat (last edited 2020-09-25 04:26:54 by MattHarbison)