Documentation: add ReviewingGuidelines

Add a reviewing guidelines document including advice and common terminology
used in Git mailing list reviews. The document is included in the
'TECH_DOCS' list in order to include it in Git's published documentation.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Helped-by: Derrick Stolee <derrickstolee@github.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -90,6 +90,7 @@ SP_ARTICLES += howto/coordinate-embargoed-releases
 API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technical/api-index.txt, $(wildcard technical/api-*.txt)))
 SP_ARTICLES += $(API_DOCS)
 
+TECH_DOCS += ReviewingGuidelines
 TECH_DOCS += MyFirstContribution
 TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches

Documentation/ReviewingGuidelines.txt

@@ -0,0 +1,162 @@
+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]