Contributing to development

We welcome contributions to the code base and development of new features for the MESSAGEix framework. This page contains guidelines for making such contributions. Each section requires some of the listed prerequisite knowledge and skills; use the links there to external resources about git, GitHub, Python, etc. to ensure you are able to understand and complete the steps.

This page uses RFC 2119 keywords to distinguish mandatory and optional actions. Sentences written in the imperative mood with a bold-face verb like “Do X, Y, and Z” imply the must / required keyword.

On this page:

On separate pages:

On GitHub:

File issues for bugs and enhancements

We use Github issues for several purposes:

  • Ask and answer questions about intended behaviour or issues running the framework or related models.

  • Report bugs, i.e. unintended or undocumented behaviour.

  • Request changes to exiting behaviour.

  • Request specific enhancements and new features, both urgent and long-term/low-priority.

  • Discuss and design of other improvements.

Please search through open and closed issues for both the message_ix and ixmp repositories. Review any related issues. Then, if your issue is not found, open a new one.

Contribute code via pull requests

1. Choose a repository

Decide which part of the MESSAGEix software stack is the appropriate location for your code:

ixmp

Contributions not specific to MESSAGEix model framework, e.g. that could be used for other, non-MESSAGE models.

Also: - genno —for core features underlying Postprocessing and reporting. - ixmp_source (closed source) —Java / JDBC backend for ixmp.

message_ix

Contributions not specific to any particular MESSAGEix model instance. Additions to this package should be usable in any MESSAGE-scheme model.

message_ix_models

Contributions to the MESSAGE-GLOBIOM family of models, including the global model, and its documentation.

Register a GitHub account, if you do not already have one.

Choose either a fork of the given repository (under your own GitHub account), or repository itself.

  • IIASA staff and core contributors with ‘Write’ permissions on may use branches within the main repositories. In some cases, these simplify testing and continuous integration checks.

  • All others, and core contributors in all other cases, should use forks.

2. Create a branch and add commits

Create a branch with an appropriate name:

  • Use ‘kebab case’ all-lower-case-with-hyphens. Underscores (_) and capital letters are slower to type; don’t use them.

  • Use prefixes as appropriate:

    • If you are addressing or closing a specific issue: issue/1234.

    • If you are adding an entirely new feature: enh/do-something or feature/do-something.

    • If you are developing for a particular message_ix_models project: project/abc. For projects that have many PRs and branches over time, use a suffix as well, for instance with the year, month, or week: project/abc/2025-w14.

  • Do not use the main branch in your fork for a PR. This makes it difficult for others to check out, use, and contribute to your code.

Push the branch to the main repository or your fork.

3. Open a pull request

  • Open a pull request (e.g. on message_ix) to merge your code into the main branch or other target branch.

  • Assign yourself and/or anyone else who will actually commit changes to the PR branch, or be actively involved in discussing/designing the code.

  • Choose the ‘draft’ status if the code on the branch is not yet complete and ready for review. (Developing code in draft PRs is good development practice: it ensures the automatic checks pass as you add to the code on your branch.)

  • Apply any appropriate labels. If a PR is to close or address an issue, these labels should match the ones on the issue.

3a. Use the template to write the PR description

The repository contains a template for the pull request description that is designed to help you write a clear one. You should write at least a tentative description at the moment you open a PR: it is useful even before code is started/finished as an expression of the intended scope of the PR. Failing this, write “TBA” (“To Be Added”) or a similar placeholder where needed. In any case, complete the description before requesting review or taking the PR out of draft state (step (5) below).

The template contains in-line comments (<!-- like this -->) with instructions that should be removed as you complete them. The “PR checklist” section and its individual items must not be removed. If an item is not relevant for your PR, strike it out partly or fully and append text to explain. For example:

- [ ] ~Add or expand tests;~ coverage checks both ✅

This indicates that there were no tests added or changed—perhaps because no code was changed—but the coverage checks still pass.

- ~Add, expand, or update documentation.~ N/A, bug fix
- [x] Update release notes.

This indicates that the documentation was not changed, because a bug fix changed the code to match the documented behaviour. However, the bugfix PR itself was added to the release notes.

Revise the description if the scope or goals of the PR change, so that it remains up-to-date and useful for understanding the branch contents.

4. Ensure checks pass

MESSAGEix has several kinds of automatic, or continuous integration, checks. Other repositories may have fewer or more checks.

  • The CLA Assistant ensures you have signed the Contributor License Agreement (follow link for text). All contributors are required to sign the CLA before any pull request can be reviewed. This ensures that all future users can benefit from your contribution, and that your contributions do not infringe on anyone else’s rights.

  • GitHub Actions is used to run several workflows. These are defined by YAML files in .github/workflows/:

    pytest

    This workflow runs all Python and R tests; on Linux, macOS, and Windows; and for multiple versions of Python. It also checks that the code style is applied.

    publish

    This workflow checks that the Python package (for upload to PyPI) can be built cleanly and without errors. The package is not actually uploaded, unless this workflow is started from a release candidate tag or on the creation of a new release on GitHub.

    nightly

    These tests run daily at 05:00 UTC. They download a particular package of full-scale, MESSAGEix-GLOBIOM global model scenarios from IIASA servers. Each scenario’s outputs are compared to an expected value listed in message_ix/tests/data/scenarios.yaml. PRs that touch the GAMS code may cause the objective function values to change; the values must be updated as part of such PRs. See the comments in the file for how to temporarily enable these checks for every commit on a PR branch.

    anaconda, miniconda

    These workflows check that the package can be installed from conda-forge using Anaconda and Miniconda, respectively, on Windows only.

  • Two checks from Codecov ensure that coverage of the ‘patch’ (changed lines in the PR) is above a given threshold (the average of all other code in the package), and that coverage of the overall package does not decrease.

  • ReadTheDocs automatically builds a preview version of the documentation, including any changes on the PR branch. You may also build and view the HTML documentation on your machine to confirm that the generated HTML is as intended and conforms to the Documentation style.

Resolve any non-passing checks.

Ask for help if needed.

5. Review

Using the GitHub sidebar on your PR, request review from another MESSAGEix contributor. GitHub suggests reviewers; optionally, contact the IIASA ECE Program to ask who should review your code.

  • If you want them to follow along with progress, tag them in the PR description, like “FYI @Alice @Bob”.

  • Per (3a) above, complete the “How to review” section of the PR template so that reviewers can understand what they should look at, tasks they should perform, etc.

  • Do not request review until the code is ready to review. Doing this sends e-mail and other notifications (e.g. in Slack, the “Pull Reminders” bot sends notices every day). If the code is not yet complete and ready for review, these notifications are noise, and the colleague may be confused as to what they should do.

Address any comments raised by the reviewer(s).

6. Merge

GitHub provides three ways to incorporate a pull request: merge, rebase, and squash. Current practice for the ixmp, message_ix, and message_data repositories is:

  • Use squash and merge…

    • if the commit history for the PR is “messy”, e.g. there are many merge commits from other branches, or the author did not write well-formatted commit messages (see “Code style”, below).

    • if the PR is very old, i.e. it starts at an old commit on main. However, it is better to rebase the PR branch on the HEAD of main and then use a merge commit (below).

  • Use rebase and merge…

    • if the PR is only one or a few commits that are obviously related.

    • if the PR does not involve user-facing changes, i.e. does not need to be linked from the release notes.

  • Use merge pull request (also written “create a merge commit”) in all other cases.

    PR branches must be rebased on the HEAD of main before merging. This is because some git-based tools will display commits from main and the PR branch interleaved if their dates and times are mixed, which makes it harder to read the commit history. Rebasing avoids this problem by ensuring each PR’s commits are displayed in sequence.

Code style

  • For both commit messages and pull request (PR) titles, follow the “7 rules of a great Git commit message”.

  • For Python code:

    • Follow the PEP 8 naming conventions.

    • Use ruff to check code formatting (ruff format, which applies the “black” format) and quality (ruff check). In particular, through pyproject.toml, message_ix uses the following rule sets to ensure:

      • “F”: code is free of basic errors, equivalent to Pyflakes or flake8.

      • “E”, “W”: code conforms to PEP 8, equivalent to using pycodestyle.

      • “I”: import statements are sorted in a consistent way, equivalent to isort.

      • “C90”: the McCabe complexity of code is below a fixed threshold, equivalent to using mccabe via flake8.

    • Add type hints to new or changed functions, methods, and global variables. Check these using the mypy static type checker.

    To simplify the use of ruff and mypy, it is recommended to:

    • Configure these to run automatically within your code editor using an extension, plugin, or script. See their respective documentation for links and details. These extensions help apply the code style every time a file is saved, or even as you type.

    • Configure pre-commit to invoke these and other checks every time you do a git commit. To use this tool, install pre-commit and then install its git hooks in your local checkout of the source repository:

      uv tool install --with=pre-commit-uv pre-commit
pre-commit install -f

# Run the tools on all files to confirm they are working
pre-commit run --all-files

    • The “Code quality” job in the “pytest” workflow described above applies exactly the same checks for PR branches. PRs that fail the checks must be corrected before they can be merged.

  • For GAMS code:

    • Wrap lines at 121 characters, except for inline documentation (see below).

  • For R code: follow the style of the existing code base.

  • Jupyter notebooks (.ipynb): see Developing tutorials.

  • Other (file names, CLI, etc.): follow the style of the existing code base, e.g.:

    • Use lower-case file names and extensions.

    • Except for Python source files, prefer hyphens to underscores.

Documentation

  • Write documentation in reStructuredText (reST) format for:

    1. Python docstrings. Wrap these at the same 88 characters as ruff enforces for code.

    2. Documentation pages, doc/*.rst.

    3. Inline documentation in message_ix/model/*.gms files.

    For (2) and (3), use semantic line breaks.

  • Ensure Sphinx does not give warnings about reST syntax for new or modified documentation.

  • Use sphinx.ext.intersphinx (click for docs) to create cross-links within one project’s documentation, or across projects.

    • Understand the use of the ~ and . characters to resolve references across the project. See Syntax in the Sphinx docs.

    • See example usage in existing code.

    • Check that intersphinx links are correctly resolved, by building the docs and attempting to click new or modified links.

  • Write docstrings in the numpydoc style. This implies also PEP 257; see in particular the format for multi-line docstrings.

    Use single backticks to refer to function arguments, and asterisks for italics:

    def func(foo: str, bar: str) -> float:
    """Perform some action.

    If `foo` and `bar` have the same value, ``42.1`` is returned. *Nice!*
    """

References:

Manage issues and pull requests

  • Assign an issue or PRs to the person(s) who must take the next action towards completing it. For example:

    • Comment on the issue to provide information/decisions needed to move forward.

    • Implement the requested changes in code.

    This might be different from the person who opened the issue/PR.

  • Use the GitHub auto-linking feature to make clear the connection between related issues and PRs.

  • Look at the labels, milestones, and projects in the right sidebar. Associate the issue with the correct one(s).

  • Follow-up on old issues (ones with no activity for a month or more):

    • Ask (in a new comment, on Slack, in person) the assignee or last commenter what the status is.

    • Close or re-assign, with a comment that describes your reasoning.