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Contributing

We appreciate all kinds of help, so thank you!

Contributing to Qiskit Terra

You can contribute in many ways to this project.

Issue reporting

This is a good point to start, when you find a problem please add it to the issue tracker. The ideal report should include the steps to reproduce it.

Doubts solving

To help less advanced users is another wonderful way to start. You can help us close some opened issues. This kind of tickets should be labeled as question.

Improvement proposal

If you have an idea for a new feature please open a ticket labeled as enhancement. If you could also add a piece of code with the idea or a partial implementation it would be awesome.

Contributor License Agreement

We'd love to accept your code! Before we can, we have to get a few legal requirements sorted out. By signing a contributor license agreement (CLA), we ensure that the community is free to use your contributions.

When you contribute to the Qiskit Terra project with a new pull request, a bot will evaluate whether you have signed the CLA. If required, the bot will comment on the pull request, including a link to accept the agreement. The individual CLA document is available for review as a PDF.

Note

If you work for a company that wants to allow you to contribute your work, then you'll need to sign a corporate CLA and email it to us at qiskit@us.ibm.com.

Good first contributions

You are welcome to contribute wherever in the code you want to, of course, but we recommend taking a look at the "Good first contribution" label into the issues and pick one. We would love to mentor you!

Doc

Review the parts of the documentation regarding the new changes and update it if it's needed.

Pull requests

We use GitHub pull requests to accept the contributions.

A friendly reminder! We'd love to have a previous discussion about the best way to implement the feature/bug you are contributing with. This is a good way to improve code quality in our beloved Qiskit!, so remember to file a new Issue before starting to code for a solution.

So after having discussed the best way to land your changes into the codebase, you are ready to start coding (yay!). We have two options here:

  1. You think your implementation doesn't introduce a lot of code, right?. Ok, no problem, you are all set to create the PR once you have finished coding. We are waiting for it!
  2. Your implementation does introduce many things in the codebase. That sounds great! Thanks!. In this case you can start coding and create a PR with the word: [WIP] as a prefix of the description. This means "Work In Progress", and allow reviewers to make micro reviews from time to time without waiting for the big and final solution... otherwise, it would make reviewing and coming changes pretty difficult to accomplish. The reviewer will remove the [WIP] prefix from the description once the PR is ready to merge.
Pull request checklist

When submitting a pull request and you feel it is ready for review, please double check that:

  • the code follows the code style of the project. For convenience, you can execute make style and make lint locally, which will print potential style warnings and fixes.
  • the documentation has been updated accordingly. In particular, if a function or class has been modified during the PR, please update the docstring accordingly.
  • your contribution passes the existing tests, and if developing a new feature, that you have added new tests that cover those changes.
  • you add a new line to the CHANGELOG.rst file, in the UNRELEASED section, with the title of your pull request and its identifier (for example, "Replace OldComponent with FluxCapacitor (#123)".
Commit messages

Please follow the next rules for the commit messages:

  • It should include a reference to the issue ID in the first line of the commit, and a brief description of the issue, so everybody knows what this ID actually refers to without wasting to much time on following the link to the issue.
  • It should provide enough information for a reviewer to understand the changes and their relation to the rest of the code.

A good example:

Issue #190: Short summary of the issue
* One of the important changes
* Another important change

Installing Qiskit Terra from source

Please see the Installing Qiskit Terra from Source section of the Qiskit documentation.

Test

New features often imply changes in the existent tests or new ones are needed. Once they're updated/added run this be sure they keep passing.

For executing the tests, a make test target is available. The execution of the tests (both via the make target and during manual invocation) takes into account the LOG_LEVEL environment variable. If present, a .log file will be created on the test directory with the output of the log calls, which will also be printed to stdout. You can adjust the verbosity via the content of that variable, for example:

Linux and Mac:

$ cd out
out$ LOG_LEVEL="DEBUG" ARGS="-V" make test

Windows:

$ cd out
C:\..\out> set LOG_LEVEL="DEBUG"
C:\..\out> set ARGS="-V"
C:\..\out> make test

For executing a simple python test manually, we don't need to change the directory to out, just run this command:

Linux and Mac:

$ LOG_LEVEL=INFO python -m unittest test/python/circuit/test_circuit_operations.py

Windows:

C:\..\> set LOG_LEVEL="INFO"
C:\..\> python -m unittest test/python/circuit/test_circuit_operations.py

Note many of the tests will not be executed unless you have setup an IBMQ account. To set this up please go to this page and register an account.

By default, and if there is no user credentials available, the tests that require online access are run with recorded (mocked) information. This is, the remote requests are replayed from a test/cassettes and not real HTTP requests is generated. If user credentials are found, in that cases it use them to make the network requests.

How and which tests are executed is controlled by a environment variable QISKIT_TESTS. The options are (where uc_available = True if the user credentials are available, and False otherwise):

Option Description Default If True, forces
skip_online Skips tests that require remote requests (also, no mocked information is used). Does not require user credentials. False rec = False
mock_online It runs the online tests using mocked information. Does not require user credentials. not uc_available skip_online = False
run_slow It runs tests tagged as slow. False  
rec It records the remote requests. It requires user credentials. False skip_online = False run_slow = False

It is possible to provide more than one option separated with commas. The order of precedence in the options is right to left. For example, QISKIT_TESTS=skip_online,rec will set the options as skip_online == False and rec == True.

Alternatively, the make test_ci target can be used instead of make test in order to run in a setup that replicates the configuration we used in our CI systems more closely.

Style guide

Please submit clean code and please make effort to follow existing conventions in order to keep it as readable as possible. We use Pylint and PEP 8 style guide: to ensure your changes respect the style guidelines, run the next commands:

All platforms:

$> cd out
out$> make lint
out$> make style

Documentation

The documentation for Qiskit Terra is in the docs directory of Qiskit repository. See this repository for more information, however, the reference documentation is auto-generated from the python docstrings throughout the code using Sphinx. Please follow Google's Python Style Guide for docstrings. A good example of the style can also be found with sphinx's napolean converter documentation.

Development cycle

Our development cycle is straightforward, use the project boards in Github for project management and use milestones for releases. The features that we want to include in these releases will be tagged and discussed in the project boards. Whenever a new release is close to be launched, we'll announce it and detail what has changed since the latest version in our Release Notes and Changelog. The channels we'll use to announce new releases are still being discussed, but for now, you can follow us on Twitter!

Branch model

There are two main branches in the repository:

  • master
    • This is the development branch.
    • Next release is going to be developed here. For example, if the current latest release version is r1.0.3, the master branch version will point to r1.1.0 (or r2.0.0).
    • You should expect this branch to be updated very frequently.
    • Even though we are always doing our best to not push code that breaks things, is more likely to eventually push code that breaks something... we will fix it ASAP, promise :).
    • This should not be considered as a stable branch to use in production environments.
    • The API of Qiskit could change without prior notice.
  • stable
    • This is our stable release branch.
    • It's always synchronized with the latest distributed package, as for now, the package you can download from pip.
    • The code in this branch is well tested and should be free of errors (unfortunately sometimes it's not).
    • This is a stable branch (as the name suggest), meaning that you can expect stable software ready for production environments.
    • All the tags from the release versions are created from this branch.

Release cycle

From time to time, we will release brand new versions of Qiskit Terra. These are well-tested versions of the software.

When the time for a new release has come, we will:

  1. Merge the master branch with the stable branch.
  2. Create a new tag with the version number in the stable branch.
  3. Crate and distribute the pip package.
  4. Change the master version to the next release version.
  5. Announce the new version to the world!

The stable branch should only receive changes in the form of bug fixes, so the third version number (the maintenance number: [major].[minor].[maintenance]) will increase on every new change.

Stable Branch Policy

The stable branch is intended to be a safe source of fixes for high impact bugs and security issues which have been fixed on master since a release. When reviewing a stable branch PR we need to balance the risk of any given patch with the value that it will provide to users of the stable branch. Only a limited class of changes are appropriate for inclusion on the stable branch. A large, risky patch for a major issue might make sense. As might a trivial fix for a fairly obscure error handling case. A number of factors must be weighed when considering a change:

  • The risk of regression: even the tiniest changes carry some risk of breaking something and we really want to avoid regressions on the stable branch
  • The user visible benefit: are we fixing something that users might actually notice and, if so, how important is it?
  • How self-contained the fix is: if it fixes a significant issue but also refactors a lot of code, it’s probably worth thinking about what a less risky fix might look like
  • Whether the fix is already on master: a change must be a backport of a change already merged onto master, unless the change simply does not make sense on master.

Backporting procedure:

When backporting a patch from master to stable we want to keep a reference to the change on master. When you create the branch for the stable PR you can use:

$ git cherry-pick -x $master_commit_id

However, this only works for small self contained patches from master. If you need to backport a subset of a larger commit (from a squashed PR for example) from master this just need be done manually. This should be handled by adding:

Backported from: #master pr number

in these cases, so we can track the source of the change subset even if a strict cherry pick doesn't make sense.

If the patch you’re proposing will not cherry-pick cleanly, you can help by resolving the conflicts yourself and proposing the resulting patch. Please keep Conflicts lines in the commit message to help review of the stable patch.

Backport Tags

Bugs or PRs tagged with stable backport potential are bugs which apply to the stable release too and may be suitable for backporting once a fix lands in master. Once the backport has been proposed, the tag should be removed.

The PR against the stable branch should include [stable] in the title, as a sign that setting the target branch as stable was not a mistake. Also, reference to the PR number in master that you are porting.