Maintainers Guide

This document defines a maintainer as a contributor with merge privileges. The information detailed here is mostly related to Qiskit releases and other internal processes.

Stable Branch Policy

The stable branch is intended to be a safe source of fixes for high-impact bugs and security issues that have been fixed on master since a release. When reviewing a stable branch PR, we must 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 visibility 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, 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, do this manually. In these cases, add:

Backported from: #master pr number

so that 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 labels

Bugs or PRs tagged with stable backport potential are bugs that 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.

Include [Stable] in the title of the PR against the stable branch, 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.

Qiskit Versioning

The Qiskit project is made up of several elements each performing different functionality. Each is independently useful and can be used on their own, but for convenience we provide this repository and meta-package to provide a single entrypoint to install all the elements at once. This is to simplify the install process and provide a unified interface to end users. However, because each Qiskit element has its own releases and versions, some care is needed when dealing with versions between the different repositories. This document outlines the guidelines for dealing with versions and releases of both Qiskit elements and the meta-package.

For the rest of this guide the standard Semantic Versioning nomenclature will be used of: Major.Minor.Patch to refer to the different components of a version number. For example, if the version number was 0.7.1, then the major version is 0, the minor version 7, and the patch version 1.

Meta-package Version

The Qiskit meta-package version is an independent value that is determined by the releases of each of the elements being tracked. Each time we push a release to a tracked component (or add an element) the meta-package requirements, and version will need to be updated and a new release published. The timing should be coordinated with the release of elements to ensure that the meta-package releases track with element releases.

Adding New Tracked Elements

When a new Qiskit element is being added to the meta-package requirements, we need to increase the Minor version of the meta-package.

For example, if the meta-package is tracking 2 elements qiskit-aer and qiskit-terra and its version is 0.7.4. Then we release a new element qiskit-new that we intend to also have included in the meta-package. When we add the new element to the meta-package we increase the version to 0.8.0.

Patch Version Increases

When any Qiskit element that is being already tracked by the meta-package releases a patch version to fix bugs in a release, we need also bump the requirement in the setup.py and then increase the patch version of the meta-package.

For example, if the meta-package is tracking 2 elements qiskit-terra==0.8.1 and qiskit-aer==0.2.1, with the current version 0.9.6. When qiskit-terra release a new patch version to fix a bug 0.8.2 the meta-package will also need to increase its patch version and release, becoming 0.9.7.

Additionally, there are occasionally packaging or other bugs in the meta-package itself that need to be fixed by pushing new releases. When those are encountered we should increase the patch version to differentiate it from the broken release. Do not delete the broken or any old releases from pypi in any situation, instead just increase the patch version and upload a new release.

Minor Version Increases

Besides when adding a new element to the meta-package, the minor version of the meta-package should also be increased anytime a minor version is increased in a tracked element.

For example, if the meta-package is tracking 2 elements qiskit-terra==0.7.0 and qiskit-aer==0.1.1 and the current version is 0.7.5. When the qiskit-aer element releases 0.2.0 then we need to increase the meta-package version to be 0.8.0 to correspond to the new release.

Major Version Increases

The major version is different from the other version number components. Unlike the other version number components, which are updated in lock step with each tracked element, the major version is only increased when all tracked versions are bumped (at least before 1.0.0). Right now, all the elements still have a major version number component of 0, and until each tracked element in the meta-repository is marked as stable by bumping the major version to be >=1, then the meta-package version should not increase the major version.

The behavior of the major version number component tracking after when all the elements are at >=1.0.0 has not been decided yet.

Optional Extras

In addition to the tracked elements, there are additional packages built on top of Qiskit which are developed in tandem with Qiskit, for example, the application repositories like qiskit-optimization. For convienence these packages are tracked by the Qiskit metapackage as optional extras that can be installed with Qiskit. Releases of these optional downstream projects do not trigger a metapackage release as they are unpinned and do not affect the metapackage version. If there is a compatibility issue between Qiskit and these downstream optional dependencies and the minimum version needs to be adjusted in a standalone release, this will only be done as a patch version release as it’s a packaging bugfix.

Qiskit Element Requirement Tracking

While not strictly related to the meta-package and Qiskit versioning, how we track the element versions in the meta-package’s requirements list is important. Each element listed in the setup.py should be pinned to a single version. This means that each version of Qiskit should only install a single version for each tracked element. For example, the requirements list at any given point should look something like:

requirements = [
    "qiskit_terra==0.7.0",
    "qiskit-aer==0.1.1",
]

This is to aid in debugging, but also make tracking the versions across multiple elements more transparent.

Documentation Structure

The way documentation is structured in Qiskit is to push as much of the actual documentation into the docstrings as possible. This makes it easier for additions and corrections to be made during development, because the majority of the documentation lives near the code being changed. There are three levels in the normal documentation structure in Terra:

The .rst files in the docs/apidocs

These files are used to tell Sphinx which modules to include in the rendered documentation. This contains two pieces of information: an internal reference or cross reference to the module, which can be used for internal links inside the documentation, and an automodule directive used to parse the module docstrings from a specified import path. For example, the dagcircuit.rst file contains:

.. _qiskit-dagcircuit:


.. automodule:: qiskit.dagcircuit
   :no-members:
   :no-inherited-members:
   :no-special-members:

The only .rst file outside of this is qiskit.rst, which contains the table of contents. If you’re adding a new .rst file for a new module’s documentation, make sure to add it to the toctree in that file.

The module-level docstring

This docstring is at the module level for the module specified in the automodule directive in the rst file. If the module specified is a directory/namespace, the docstring should be specified in the __init__.py file for that directory. This module-level docstring contains more details about the module being documented. The normal structure to this docstring is to outline all the classes and functions of the public API that are contained in that module. This is typically done using the autosummary directive (or autodoc directives directly if the module is simple, such as in the case of qiskit.execute). The autosummary directive is used to autodoc a list of different Python elements (classes, functions, etc.) directly without having to manually call out the autodoc directives for each one. The module-level docstring is where to provide a high-level overview of what functionality the module provides. This is normally done by grouping the different components of the public API together into multiple subsections.

For example, as in the previous dagcircuit module example, the contents of the module docstring for qiskit/dagcircuit/__init__.py would be:

"""
=======================================
DAG Circuits (:mod:`qiskit.dagcircuit`)
=======================================
.. currentmodule:: qiskit.dagcircuit
DAG Circuits
============
.. autosummary::
   :toctree: ../stubs/
   DAGCircuit
   DAGNode
Exceptions
==========
.. autosummary::
   :toctree: ../stubs/
   DAGCircuitError
"""

Note

This is just an example and the actual module docstring for the dagcircuit module might diverge from this.

The actual docstring for the elements listed in the module docstring

You should strive to document thoroughly all the public interfaces exposed using examples when necessary. For docstrings, Google Python Style Docstrings are used. This is parsed using the napoleon sphinx extension. The napoleon documentation contains a good example of how docstrings should be formatted.

Note

You can use any Sphinx directive or rst formatting in a docstring as it makes sense. For example, one common extension used is the jupyter-execute directive, which is used to execute a code block in Jupyter and display both the code and output. This is particularly useful for visualizations.

Documentation Integration

The hosted documentation at https://qiskit.org/documentation/ covers the entire Qiskit project; Terra is just one component of that. As such, the documentation builds for the hosted version are built by the Qiskit meta-package repository https://github.com/Qiskit/qiskit. When commits are merged to that repo, the output of Sphinx builds are uploaded to the qiskit.org website. Those Sphinx builds are configured to pull in the documentation from the version of the Qiskit elements installed by the meta-package at that point. For example, if the meta-package version is currently 0.13.0, then that will copy the documentation from Terra’s 0.10.0 release. When the meta-package’s requirements are bumped, then it will start pulling documentation from the new version. This means that fixes for incorrect API documentation will need to be included in a new release. Documentation fixes are valid backports for a stable patch release per the stable branch policy (see Stable Branch Policy).

During the build process, the contents of each element’s docs/apidocs/ are recursively copied into a shared copy of doc/apidocs/ in the meta-package repository along with all the other elements. This means that what is in the root of docs/apidocs on each element at a release will end up on the root of https://qiskit.org/documentation/apidoc/.