Contributing to Qiskit Metal¶

Qiskit Metal is an open-source project committed to bringing quantum hardware design to people of all backgrounds. This page describes how you can join the Qiskit Metal community in this goal.

Where Things Are¶

The code for Qiskit Metal is located in the Qiskit GitHub organization, as part of the larger umbrella of Qiskit projects.

Reporting Bugs and Requesting Enhancements¶

When you encounter a problem, please open an issue in the issue tracker: https://github.com/Qiskit/qiskit-metal/issues

When reporting an issue, please follow this template:

<!--- Provide a general summary of the issue in the Title above -->

## Expected Behavior
<!--- Tell us what should happen -->

## Current Behavior
<!--- Tell us what happens instead of the expected behavior -->

## System Settings
<!--- Post the results of `metal.about()` here. --->

## Steps to Reproduce
<!--- Provide a link to a live example, or an unambiguous set of steps to -->
<!--- reproduce this bug. Include code to reproduce, if relevant -->
1.
2.
3.

## Detailed Description
<!--- Provide a detailed description of the change or addition you are proposing -->

## Possible Implementation
<!--- Not obligatory, but suggest an idea for implementing addition or change -->

If you have an idea for a new feature, please open an Enhancement issue in the repository issue tracker. Opening an issue starts a discussion with the team about your idea, how it fits in with the project, how it can be implemented, etc.

Contributing Code¶

Style Guide¶

To enforce a consistent code style in the project, we use customized Pylint for linting and YAPF`<https://github.com/google/yapf>__ with the `Google style for auto formatting. The custom .pylintrc and .style.yapf files is located in the root of the repository. Our CI pipeline will enforce these styles when you make the pull request.

Contributor License Agreement¶

Before you can submit any code, all contributors must sign a contributor license agreement (CLA). By signing a CLA, you’re attesting that you are the author of the contribution, and that you’re freely contributing it under the terms of the Apache-2.0 license.

When you contribute to the Qiskit 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 your contribution is part of your employment or your contribution is the property of your employer, then you will more than likely need to sign a corporate CLA too and email it to us at <qiskit@us.ibm.com>.

Pull Requests¶

We use GitHub pull requests to accept contributions.

While not required, opening a new issue about the bug you’re fixing or the feature you’re working on before you open a pull request is an important step in starting a discussion with the community about your work. The issue gives us a place to talk about the idea and how we can work together to implement it in the code. It also lets the community know what you’re working on, and if you need help, you can reference the issue when discussing it with other community and team members.

If you’ve written some code but need help finishing it, want to get initial feedback on it prior to finishing it, or want to share it and discuss prior to finishing the implementation, you can open a Work in Progress pull request. This will indicate to reviewers that the code in the PR isn’t in its final state and will change. It also means that we will not merge the commit until it is finished. You or a reviewer can remove the WIP status when the code is ready to be fully reviewed for merging.

Code Review¶

Code review is done in the open and is open to anyone. While only maintainers have access to merge commits, community feedback on pull requests is extremely valuable. It is also a good mechanism to learn about the code base. You can view a list of all open pull requests at https://github.com/Qiskit/qiskit-metal/pulls

Commit Messages¶

The content of the commit message describing a change is just as important as the change itself. The commit message provides the context for not only code review but also the change history in the git log. A detailed commit message will make it easier for your code to be reviewed, and will also provide context to the change when someone looks at it in the future. When writing a commit message, remember these important details:

Do not assume the reviewer understands what the original problem was.

When reading an issue, after a number of back & forth comments, it is often clear what the root cause problem is. The commit message should have a clear statement as to what the original problem is. The bug is merely interesting historical background on how the problem was identified. It should be possible to review a proposed patch for correctness from the commit message, without needing to read the bug ticket.

Do not assume the code is self-evident/self-documenting.

What is self-evident to one person, might not be clear to another person. Always document what the original problem was and how it is being fixed, for any change except the most obvious typos, or whitespace-only commits.

Describe why a change is being made.

A common mistake is only to document how the code has been written, without describing why the developer chose to do it that way. Certainly, you should describe the overall code structure, particularly for large changes, but more importantly, be sure to describe the intent/motivation behind the changes.

Read the commit message to see if it hints at improved code structure.

Often when describing a large commit message, it becomes obvious that a commit should have been split into two or more parts. Don’t be afraid to go back and rebase the change to split it up into separate pull requests.

Ensure sufficient information to decide whether to review.

When GitHub sends out email alerts for new pull request submissions, there is minimal information included - usually just the commit message and the list of files changes. Because of the high volume of patches, a commit message must contain sufficient information for potential reviewers to find the patch that they need to review.

The first commit line is the most important.

In Git commits, the first line of the commit message has special significance. It is used as the default pull request title, email notification subject line, git annotate messages, gitk viewer annotations, merge commit messages, and many more places where space is at a premium. As well as summarizing the change itself, it should take care to detail what part of the code is affected.

In addition, the first line of the commit message becomes an entry in the generated changelog if the PR is tagged as being included in the changelog. It is critically important that you write clear and succinct summary lines.

Describe any limitations of the current code.

If the code being changed still has future scope for improvements, or any known limitations, mention these in the commit message. This demonstrates to the reviewer that the broader picture has been considered, and what tradeoffs have been done in terms of short-term goals versus long-term wishes.

Include references to issues.

If the commit fixes are related to an issue, make sure you annotate that in the commit message. Use the syntax:

Fixes #1234

if it fixes the issue (GitHub will close the issue when the PR merges).

The main rule to follow is:

The commit message must contain all the information required to fully understand and review the patch for correctness. Less is not more.

Documenting Your Code¶

If you make a change to an element, make sure you update the associated docstrings and parts of the documentation under docs/apidocs in the corresponding repo. To locally build the element-specific documentation, run tox -edocs to compile and build the documentation locally and save the output to docs/_build/html. Additionally, the Docs CI job on azure pipelines will run this and host a zip file of the output that you can download and view locally.

You can open a documentation issue if you see doc bugs, have a new feature that needs to be documented, or think that material could be added to the existing docs.

Good First Contributions¶

If you would like to contribute to Qiskit Metal, but aren’t sure where to get started, the good first issue label on issues for a project highlights items appropriate for people new to the project. These are all issues that have been reviewed and tagged by contributors as something a new contributor should be able to work on. In other words, intimate familiarity with Qiskit Metal is not a requirement to develop a fix for the issue.

Deprecation Policy¶

Qiskit users need to know if a feature or an API they rely upon will continue to be supported by the software tomorrow. Knowing under which conditions the project can remove (or change in a backwards-incompatible manner) a feature or API is important to the user. To manage expectations, the following policy is how API and feature deprecation/removal is handled by Qiskit:

1. Features, APIs, or configuration options are marked deprecated in the code. Appropriate DeprecationWarning class warnings will be sent to the user. The deprecated code will be frozen and receive only minimal maintenance (just so that it continues to work as-is).

2. A migration path will be documented for current users of the feature. This will be outlined in the both the release notes adding the deprecation, and the release notes removing the feature at the completion of the deprecation cycle. If feasible, the warning message will also include the migration path. A migration path might be “stop using that feature”, but in such cases it is necessary to first judge how widely used and/or important the feature is to users, in order to determine a reasonable obsolescence date.

3. An obsolescence date for the feature will be set. The feature must remain intact and working (although with the proper warning being emitted) in all releases pushed until after that obsolescence date. At the very minimum, the feature (or API, or configuration option) should be marked as deprecated (and continue to be supported) for at least three months of linear time from the release date of the first release to include the deprecation warning.

Note that this delay is a minimum. For significant features, it is recommended that the deprecated feature appears for at least double that time. Also, per the stable branch policy, deprecation removals can only occur during minor version releases; they are not appropriate for backporting.

Deprecation Warnings¶

The proper way to raise a deprecation warning is to use the warn function from the warnings module in the Python standard library. The warning category class should be a DeprecationWarning. An example would be:

import warnings

def foo(input):
    warnings.warn('The qiskit.foo() function is deprecated as of 0.9.0, and '
                  'will be removed no earlier than 3 months after that '
                  'release date. You should use the qiskit.bar() function '
                  'instead.', DeprecationWarning, stacklevel=2)

One thing to note here is the stack_level kwarg on the warn() call. This argument is used to specify which level in the call stack will be used as the line initiating the warning. Typically, stack_level should be set to 2, as this will show the line calling the context where the warning was raised. In the above example, it would be the caller of foo(). If you did not set this, the warning would show that it was caused by the line in the foo() function, which is not helpful for users trying to determine the origin of a deprecated call. However, this value may be adjusted, depending on the call stack and where warn() gets called from. For example, if the warning is always raised by a private method that only has one caller, stack_level=3 might be appropriate.

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.

Custom Names and Images for QComponents¶

When adding new qcomponents, new images for these components go in the following directory:

qiskit-metal/qiskit_metal/_gui/_imgs/components

In the qcomponent file itself, the following attribute somewhere in the comments will tell the application which image corresponds to this file:

.. image::
    myqcomponent.png

The meta attribute can used to add a custom display name to the file:

.. meta::
    MyQComponent

If you had a file with the previous two attributes, the user is telling the qiskit metal application that the image for the qcomponent is named myqcomponent.png and is located in:

qiskit-metal/qiskit_metal/_gui/_imgs/components/myqcomponent.png

and that they want the display name of this file to be MyQComponent.

Contributing to Documentation¶

Qiskit Metal documentation is shaped by the docs as code philosophy, primarily drawn from Qiskit Metal code comments in the style of API documentation.

The documentation is built using Sphinx. The majority of documentation, under API Reference, is drawn from code comments in the repositories listed in Where Things Are.

Documentation Structure¶

The way documentation is structured in Qiskit Metal 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 Metal:

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 analyses.rst file contains

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/analyses/__init__.py would be

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.

Rebuilding Documentation¶

As you make changes to your local RST files, you can update your HTML files by navigating to /docs/ and running the following in a terminal window:

make html

This will build a styled, HTML version of your local documentation repository in the subdirectory /docs/_build/html/.

Tutorials¶

Jupyter notebook tutorials showing off features of Qiskit Metal are located in the _tutorials_ folder. If you add a new feature, please add a demonstration of its use to a notebook or start a new notebook.