[RFC] Add Commit Message Guideline (#88)

* [RFC] Add Commit Message Guideline

This RFC proposes adding a Commmit Message Guideline to Apache TVM
documentation to help guide contributors on how to write good commit
messages when submitting code / Pull Requests.

Co-authored-by: Leandro Nunes <leandro.nunes@arm.com>

* Remove out-of-scope paragraph

As per the reviews, remove this paragraph since multiple commits / changes in a
PR is out-of-scope, best fits in another guideline, and would require
addtional discussions, needing a separate vote.

* Be more explicit about committer and author responsibilities

Be more explicit about committer and author responsibilities when
the PR title and/or body need to get updated to be in sync with the code
changes after a review cycle.

* Clarify about capitalization in tags

Clarify about the preferred capitalization in tags. Also clarify about
multiple tags and acronyms when used as a tag.

* Be more emphatic about no need of a period at the end of the title

Be more emphatic about no need of a period at the end of the title but
don't enforce it.

* Make it clear that tag is enforced but capitalization is not

Original proposal for this RFC had tag presence as an enforced rule.
Later, text on recommendation about tag capitalization was added to the
rule and it became a tad unclear if the enforcement applies to the tag
presence only or also to the tag capitalization text.

This commit moves the "enforced" mark before the tag capitalization text
to make it clearer that it applies to the tag presence only. It also
tweaks a bit the text to avoid the idea that tag presence is optional --
since it's enforced, just like it was in the original proposal.

* Update rfcs/0088-commit-message-guideline.md

Co-authored-by: Siyuan Feng <Hzfengsy@sjtu.edu.cn>

Co-authored-by: Leandro Nunes <leandro.nunes@arm.com>
Co-authored-by: Siyuan Feng <Hzfengsy@sjtu.edu.cn>

rfcs/0088-commit-message-guideline.md

@@ -0,0 +1,186 @@
+- Feature Name: Commit Message Guideline
+- Start Date: 2022-08-12
+- RFC PR: [apache/tvm-rfcs#0088](https://github.com/apache/tvm-rfcs/pull/88)
+
+# Summary
+[summary]: #summary
+
+This RFC proposes adding a Commmit Message Guideline to TVM documentation to
+help guide contributors on how to write good commit messages when submitting
+code / PRs (Pull Requests) to Apache TVM.
+
+# Motivation
+[motivation]: #motivation
+
+Currently TVM commit logs are less than ideal because many commit messages lack
+valuable information and don't follow any format standard.
+
+Valuable information is usually left behind in Github PR conversations or
+discussion threads in the Discuss forum, making it hard to retrieve them when
+inspecting the commit messages -- using `git log`, for instance.
+
+Because commit messages are an indirect but important aspect of code quality,
+and also important for code maintenance, it is essential for a long term open
+source project to ensure that they meet high standards.
+
+The importance of commit messages conveying enough context and information about
+the code being changed will grow as the project grows and bad (poorly written)
+commit messages can affect negatively the code quality of future changes that
+would otherwise benefit from past good commit messages if they existed.
+
+Beyond code itself, poorly written commit messages can also affect the community
+in other ways. For example, by not providing to new contributors a consistent
+and complete history or context for the code changes, it can work as a barrier
+for new contributions because much more time will be necessary trying to
+understand what motivated a past critical but unclear change.
+
+Hence this Commit Message Guideline can help contributors to write good commit
+messages and so improve the current situation regarding the TVM commit logs.
+
+# Guide-level explanation
+[guide-level-explanation]: #guide-level-explanation
+
+Commit Message Guideline
+
+Apache TVM uses the Github (GH) platform for patch submission and code review
+via Pull Requests (PRs). The final commit (title and body) that is merged into
+the Apache TVM main tree is composed of the PR's title and body and must be kept
+updated and reflecting the new changes in the code as per the reviews and
+discussions.
+
+Although these guidelines apply essentially to the PRs’ title and body messages,
+because GH auto-generates the PR’s title and body from the commits on a given
+branch, it’s recommended to follow these guidelines right from the beginning,
+when preparing commits in general to be submitted to the Apache TVM project.
+This will ease the creation of a new PR, avoiding rework, and also will help the
+review.
+
+The rules below will help to achieve uniformity that has several benefits, both
+for review and for the code base maintenance as a whole, helping you to write
+commit messages with a good quality suitable for the Apache TVM project,
+allowing fast log searches, bisecting, and so on.
+
+_PR/commit title_:
+
+* Guarantee a title exists (enforced);
+* Don’t use Github usernames in the title, like @username (enforced);
+* A tag must be present as a hint about what component(s) of the code
+  the PRs / commits “touch” (enforced). For example [BugFix], [CI], [microTVM],
+  and [TVMC]. Tags go between square brackets and appear first in the title. If
+  more than one tag exist, multiple brackets should be used, like [BugFix][CI].
+  The case recommended for tags, in geral, is the upper camel case. For example,
+  prefer the forms [Fix], [BugFix], and [Docker] instead of [fix], [bug_fix],
+  and [docker]. Acronyms should be kept as such so, for example, use [CI] and
+  [TVMC] instead of [ci] and [tvmc]. Tags help reviewers to identify the PRs
+  they can/want to review and also help the release folks when generating the
+  release notes;
+* Use an imperative mood. Avoid titles like “Added operator X” and “Updated
+  image Y in the CI”, instead use the forms “Add feature X” and “Update image Y
+  in the CI” instead;
+* Observe proper use of caps at the beginning (uppercase for the first letter)
+  and for acronyms, like, for instance, TVM, FVP, OpenCL. Hence instead of
+  “fix tvm use of opencl library”, write it as “Fix TVM use of OpenCL library”;
+* Do not put a period at the end of the title.
+
+_PR/commit body_:
+
+* Guarantee a body exists (enforced);
+* Don’t use Github usernames in body text, like @username (enforced);
+* Avoid “bullet” commit message bodies: “bullet” commit message bodies are not
+  bad per se, but “bullet” commit messages without any description or
+  explanation is likely as bad as commits without any description, rationale,
+  or explanation in the body.
+
+For minor deviations from these guidelines, the community will normally favor
+reminding the contributor of this policy over reverting or blocking a commmit /
+PR.
+
+Commits and PRs without a title and/or a body are not considered minor
+deviations from these guidelines and hence must be avoided.
+
+Most importantly, the contents of the commit message, especially the body,
+should be written to convey the intention of the change, so it should avoid
+being vague. For example, commits with a title like “Fix”, “Cleanup”, and
+“Fix flaky test” and without any body text should be avoided. Also, for the
+review, it will leave the reviewer wondering about what exactly was fixed or
+changed and why the change is necessary, slowing the review.
+
+Below is an example that can be used as a model:
+
+> [microTVM] Zephyr: Remove zephyr_board option from build, flash, and open_transport methods
+>
+> Currently it’s necessary to pass the board type via ‘zephyr_board’ option to
+> the Project API build, flash, and open_transport methods.
+>
+> However, since the board type is already configured when the project is
+> created (i.e. when the generate_project method is called), it’s possible to
+> avoid this redundancy by obtaining the board type from the project
+> configuration files.
+>
+> This commit adds code to obtain the board type from the project CMake files,
+> removing this option from build, flash, and open_transport methods, so it’s
+> only necessary to specify the ‘zephyr_board’ option when calling
+> generate_project.
+>
+> This commit also moves the ‘verbose’ and ‘west_cmd’ options from ‘build’
+> method to ‘generate_project’, reducing further the number of required options
+> when building a project, since the ‘build’ method is usually called more often
+> than the ‘generate_project’.
+
+After a new PR is created and the review starts it’s common that reviewers will
+request changes. Usually the author will address the reviewers’ comments and
+push additional commits on top of the initial ones. For these additional commits
+there is no recommendation regarding the commit messages. However if the
+additional commits render the PR title and/or body outdated then it's the
+author's responsibility to keep the PR title and body in sync with new changes
+in the code and updated the PR title and body accordingly (remember that the PR
+title and body will be used to compose the final commit message that will land
+in the main tree).
+
+Committers will seek to fix any issues with the commit message prior to
+committing but they retain the right to inform the author of the rules and
+encourage them to follow them in future. Also, they retain the right to ask to
+the author to update the PR title and/or body when they are not correctly
+updated or fixed.
+
+# Reference-level explanation
+[reference-level-explanation]: #reference-level-explanation
+
+TVM Community must reach a certain concensus about the rules in this guideline,
+hence this RFC will be voted.
+
+Once it's voted and approved the Commit Message Guideline text will be added to
+`./docs/contribute/pull_request.rst` doc, under section 'Submit a Pull Request',
+below subsection 'Guidelines', as a subsection named “Commit Message Guideline”.
+The text in the second-last item in subsection 'Guidelines' that mentions PR
+tags will also be extended (a hyperlink will be added) to refer to this
+guideline, since it also contains guidelines about use of tags.
+
+New contributors can consult the Commit Message Guidelilne before submitting
+PRs. Also, committers and reviewers can use this guideline when reviewing PRs in
+case some clarification or help is necessary about how an author or contributor
+should write or improve the PR's title and body.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+None.
+
+# Rationale and alternatives
+[rationale-and-alternatives]: #rationale-and-alternatives
+
+# Prior art
+[prior-art]: #prior-art
+
+This guideline is similar to other ones already being used succesfully in other
+open source projects, like gcc, Zephyr, LLVM, and Linux.
+
+# Unresolved questions
+[unresolved-questions]: #unresolved-questions
+
+# Future possibilities
+[future-possibilities]: #future-possibilities
+
+A linter can also be used with tvm-bot to enforce some rules or aspects of these
+guidelines, when pertinent. If that is implemented the rules enforced by the bot
+would be those marked with "enforce" in the guideline.