| Reviewing Patches in the Git Project |
| ==================================== |
| |
| Introduction |
| ------------ |
| The Git development community is a widely distributed, diverse, ever-changing |
| group of individuals. Asynchronous communication via the Git mailing list poses |
| unique challenges when reviewing or discussing patches. This document contains |
| some guiding principles and helpful tools you can use to make your reviews both |
| more efficient for yourself and more effective for other contributors. |
| |
| Note that none of the recommendations here are binding or in any way a |
| requirement of participation in the Git community. They are provided as a |
| resource to supplement your skills as a contributor. |
| |
| Principles |
| ---------- |
| |
| Selecting patch(es) to review |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| If you are looking for a patch series in need of review, start by checking |
| latest "What's cooking in git.git" email |
| (https://lore.kernel.org/git/xmqqilm1yp3m.fsf@gitster.g/[example]). The "What's |
| cooking" emails & replies can be found using the query `s:"What's cooking"` on |
| the https://lore.kernel.org/git/[`lore.kernel.org` mailing list archive]; |
| alternatively, you can find the contents of the "What's cooking" email tracked |
| in `whats-cooking.txt` on the `todo` branch of Git. Topics tagged with "Needs |
| review" and those in the "[New Topics]" section are typically those that would |
| benefit the most from additional review. |
| |
| Patches can also be searched manually in the mailing list archive using a query |
| like `s:"PATCH" -s:"Re:"`. You can browse these results for topics relevant to |
| your expertise or interest. |
| |
| If you've already contributed to Git, you may also be CC'd in another |
| contributor's patch series. These are topics where the author feels that your |
| attention is warranted. This may be because their patch changes something you |
| wrote previously (making you a good judge of whether the new approach does or |
| doesn't work), or because you have the expertise to provide an exceptionally |
| helpful review. There is no requirement to review these patches but, in the |
| spirit of open source collaboration, you should strongly consider doing so. |
| |
| Reviewing patches |
| ~~~~~~~~~~~~~~~~~ |
| While every contributor takes their own approach to reviewing patches, here are |
| some general pieces of advice to make your reviews as clear and helpful as |
| possible. The advice is broken into two rough categories: high-level reviewing |
| guidance, and concrete tips for interacting with patches on the mailing list. |
| |
| ==== High-level guidance |
| - Remember to review the content of commit messages for correctness and clarity, |
| in addition to the code change in the patch's diff. The commit message of a |
| patch should accurately and fully explain the code change being made in the |
| diff. |
| |
| - Reviewing test coverage is an important - but easy to overlook - component of |
| reviews. A patch's changes may be covered by existing tests, or new tests may |
| be introduced to exercise new behavior. Checking out a patch or series locally |
| allows you to manually mutate lines of new & existing tests to verify expected |
| pass/fail behavior. You can use this information to verify proper coverage or |
| to suggest additional tests the author could add. |
| |
| - When providing a recommendation, be as clear as possible about whether you |
| consider it "blocking" (the code would be broken or otherwise made worse if an |
| issue isn't fixed) or "non-blocking" (the patch could be made better by taking |
| the recommendation, but acceptance of the series does not require it). |
| Non-blocking recommendations can be particularly ambiguous when they are |
| related to - but outside the scope of - a series ("nice-to-have"s), or when |
| they represent only stylistic differences between the author and reviewer. |
| |
| - When commenting on an issue, try to include suggestions for how the author |
| could fix it. This not only helps the author to understand and fix the issue, |
| it also deepens and improves your understanding of the topic. |
| |
| - Reviews do not need to exclusively point out problems. Feel free to "think out |
| loud" in your review: describe how you read & understood a complex section of |
| a patch, ask a question about something that confused you, point out something |
| you found exceptionally well-written, etc. In particular, uplifting feedback |
| goes a long way towards encouraging contributors to participate more actively |
| in the Git community. |
| |
| ==== Performing your review |
| - Provide your review comments per-patch in a plaintext "Reply-All" email to the |
| relevant patch. Comments should be made inline, immediately below the relevant |
| section(s). |
| |
| - You may find that the limited context provided in the patch diff is sometimes |
| insufficient for a thorough review. In such cases, you can review patches in |
| your local tree by either applying patches with linkgit:git-am[1] or checking |
| out the associated branch from https://github.com/gitster/git once the series |
| is tracked there. |
| |
| - Large, complicated patch diffs are sometimes unavoidable, such as when they |
| refactor existing code. If you find such a patch difficult to parse, try |
| reviewing the diff produced with the `--color-moved` and/or |
| `--ignore-space-change` options. |
| |
| - If a patch is long, you are encouraged to delete parts of it that are |
| unrelated to your review from the email reply. Make sure to leave enough |
| context for readers to understand your comments! |
| |
| - If you cannot complete a full review of a series all at once, consider letting |
| the author know (on- or off-list) if/when you plan to review the rest of the |
| series. |
| |
| Completing a review |
| ~~~~~~~~~~~~~~~~~~~ |
| Once each patch of a series is reviewed, the author (and/or other contributors) |
| may discuss the review(s). This may result in no changes being applied, or the |
| author will send a new version of their patch(es). |
| |
| After a series is rerolled in response to your or others' review, make sure to |
| re-review the updates. If you are happy with the state of the patch series, |
| explicitly indicate your approval (typically with a reply to the latest |
| version's cover letter). Optionally, you can let the author know that they can |
| add a "Reviewed-by: <you>" trailer if they resubmit the reviewed patch verbatim |
| in a later iteration of the series. |
| |
| Finally, subsequent "What's cooking" emails may explicitly ask whether a |
| reviewed topic is ready for merging to the `next` branch (typically phrased |
| "Will merge to \'next\'?"). You can help the maintainer and author by responding |
| with a short description of the state of your (and others', if applicable) |
| review, including the links to the relevant thread(s). |
| |
| Terminology |
| ----------- |
| nit: :: |
| Denotes a small issue that should be fixed, such as a typographical error |
| or mis-alignment of conditions in an `if()` statement. |
| |
| aside: :: |
| optional: :: |
| non-blocking: :: |
| Indicates to the reader that the following comment should not block the |
| acceptance of the patch or series. These are typically recommendations |
| related to code organization & style, or musings about topics related to |
| the patch in question, but beyond its scope. |
| |
| s/<before>/<after>/:: |
| Shorthand for "you wrote <before>, but I think you meant <after>," usually |
| for misspellings or other typographical errors. The syntax is a reference |
| to "substitute" command commonly found in Unix tools such as `ed`, `sed`, |
| `vim`, and `perl`. |
| |
| cover letter:: |
| The "Patch 0" of a multi-patch series. This email describes the |
| high-level intent and structure of the patch series to readers on the |
| Git mailing list. It is also where the changelog notes and range-diff of |
| subsequent versions are provided by the author. |
| + |
| On single-patch submissions, cover letter content is typically not sent as a |
| separate email. Instead, it is inserted between the end of the patch's commit |
| message (after the `---`) and the beginning of the diff. |
| |
| #leftoverbits:: |
| Used by either an author or a reviewer to describe features or suggested |
| changes that are out-of-scope of a given patch or series, but are relevant |
| to the topic for the sake of discussion. |
| |
| See Also |
| -------- |
| link:MyFirstContribution.html[MyFirstContribution] |