[PATCH v2 0/2] cocci: codify authoring and reviewing practices

Thanks for the input on v1, all :)

I've tried to capture all of the discussion in some form. AFAICT, the result is quite similar to what we are already doing, so it might not be very helpful to folks who have already worked with Coccinelle, but it should hopefully be useful to newcomers.

I suspect that we won't converge on any new practices during this discussion, but as we develop practices in the future, we can just update this doc.

Glen Choo (2):
  cocci: add headings to and reword README
  cocci: codify authoring and reviewing practices

 contrib/coccinelle/README | 40 +++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

base-commit: f285f68a132109c234d93490671c00218066ace9
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1495%2Fchooglen%2Fpush-lsxuouxyokwo-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1495/chooglen/push-lsxuouxyokwo-v2
Pull-Request: https://github.com/git/git/pull/1495

Range-diff vs v1:

 1:  4a8b8a2a674 = 1:  4a8b8a2a674 cocci: add headings to and reword README
 2:  75feb18dfd8 ! 2:  acee642531a cocci: codify authoring and reviewing practices
     @@ Metadata
       ## Commit message ##
          cocci: codify authoring and reviewing practices
      
     -    This isn't set in stone; we expect this to be updated as the project
     -    evolves.
     +    These practices largely reflect what we are already doing on the mailing
     +    list, which should help new Coccinelle authors and reviewers get up to
     +    speed.
      
          Signed-off-by: Glen Choo <chooglen@google.com>
      
     @@ contrib/coccinelle/README: that might be useful to developers.
      +
      +== Authoring and reviewing coccinelle changes
      +
     -+* When introducing and applying a new .cocci file, both the Git changes and
     -+  .cocci file should be reviewed.
     ++* When a .cocci is made, both the Git changes and .cocci file should be
     ++  reviewed. When reviewing such a change, do your best to understand the .cocci
     ++  changes (e.g. by asking the author to explain the change) and be explicit
     ++  about your understanding of the changes. This helps us decide whether input
     ++  from coccinelle experts is needed or not. If you aren't sure of the cocci
     ++  changes, indicate what changes you actively endorse and leave an Acked-by
     ++  (instead of Reviewed-by).
      +
     -+* Reviewers do not need to be coccinelle experts. To give a Reviewed-By, it is
     -+  enough for the reviewer to get a rough understanding of the proposed rules by
     -+  comparing the .cocci and Git changes, then checking that understanding
     -+  with the author.
     -+
     -+* Conversely, authors should consider that reviewers may not be coccinelle
     -+  experts. The primary aim should be to make .cocci files easy to understand,
     -+  e.g. by adding comments or by using rules that are easier to understand even
     -+  if they are less elegant.
     ++* Authors should consider that reviewers may not be coccinelle experts, thus the
     ++  the .cocci changes may not be self-evident. A plain text description of the
     ++  changes is strongly encouraged, especially when using more esoteric features
     ++  of the language.
      +
      +* .cocci rules should target only the problem it is trying to solve; "collateral
     -+  damage" is not allowed.
     ++  damage" is not allowed. Reviewers should look out and flag overly-broad rules.
     ++
     ++* Consider the cost-benefit ratio of .cocci changes. In particular, consider the
     ++  effect on the runtime of "make coccicheck", and how often your .cocci check
     ++  will catch something valuable. As a rule of thumb, rules that can bail early
     ++  if a file doesn't have a particular token will have a small impact on runtime,
     ++  and vice-versa.
      +
      +* .cocci files used for refactoring should be temporarily kept in-tree to aid
     -+  the refactoring of out-of-tree code (e.g. in-flight topics). They should be
     -+  removed when enough time has been given for others to refactor their code,
     -+  i.e. ~1 release cycle.
     ++  the refactoring of out-of-tree code (e.g. in-flight topics). Periodically
     ++  evaluate the cost-benefit ratio to determine when the file should be removed.
     ++  For example, consider how many out-of-tree users are left and how much this
     ++  slows down "make coccicheck".