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Re: New semantic patches vs. in-flight topics [was: Re: [PATCH 00/19] Bring more repository handles into our code base]

From
SZEDER Gábor <szeder.dev@gmail.com>
Date
Oct 25, 2018, 01:59 UTC
Message-ID
<20181025015910.GJ30222@szeder.dev>
In-Reply-To
<CAGZ79kboyakR=dARH60ZJmyN=kT+-X0SSDjgz3aswpkUd+bZmg@mail.gmail.com>
On Mon, Oct 22, 2018 at 11:54:06AM -0700, Stefan Beller wrote:
Show 8 quoted lines
> For the sake of a good history, I would think running 'make coccicheck'
> and applying the resulting patches would be best as part of the (dirty)
> merge of any topic that proposes new semantic patches, but that would
> add load to Junio as it would be an extra step during the merge.
> 
> One could argue that the step of applying such transformations into
> the dirty merge is cheaper than resolving merge conflicts that are
> had when the topic includes the transformation.

Please consider that merge commits' have uglier diffs than regular commits, and that merge commits cause additional complications when 'git bisect' points the finger at them, both of which are exacerbated by additional changes squeezed into evil merges.

Show 13 quoted lines
> >     Consequently, 'make coccicheck' won't run clean and the
> >     static analysis build job will fail until all those topics reach
> >     'master', and the remaining transformations are applied on top.
> >
> >     This was (and still is!) an issue with the hasheq()/oideq() series
> >     as well: that series was added on 2018-08-28, and the static
> >     analysis build job is red on 'pu' ever since.  See the follow-up
> >     patch e43d2dcce1 (more oideq/hasheq conversions, 2018-10-02), and
> >     one more follow-up will be necessary after the builtin stash topic
> >     is merged to 'master'.
> 
> In my understanding this follow up is a feature, as it helps to avoid
> merge conflicts with other topics in flight.
I don't see how such a follow up patch helps to avoid merge conflicts.

There were topics that branched off before the introduction of oideq() into 'master', therefore they couldn't make use of this new function until they were merged to 'master' as well, so they added their own !oidcmp() calls. That follow up patch was necessary to transform these new !oidcmp() calls after those topics reached 'master'. Merge conflicts had nothing to do with it.

So this follow up patch is not a feature, but rather an inherent consequence of the project's branching model, with lots of parallel running topics branching off at different points and progressing at different speeds.

> >     This makes it harder to review other patch series.
> 
> as 'make coccicheck' is an integral part of your review?

Erm, right, "review" was not the right word here. Anyway, as it is, 'make coccicheck' is an integral part of our automated tests, not only on Travis CI but on the upcoming Azure thing as well. I just try to pay attention to its results and the results of a bunch of my additional builds, and complain or even send a fix when something goes reproducibly wrong. This has certainly became more cumbersome with the permanently failing static analysis build job in the last couple of weeks.

Show 48 quoted lines
> > How about introducing the concept of "pending" semantic patches,
> > stored in 'contrib/coccinelle/<name>.pending.cocci' files, modifying
> > 'make coccicheck' to skip them, and adding the new 'make
> > coccicheck-pending' target to make it convenient to apply them, e.g.
> > something like the simple patch at the end.
> >
> > So the process would go something like this:
> >
> >   - A new semantic patch should be added as "pending", e.g. to the
> >     file 'the_repository.pending.cocci', together with the resulting
> >     transformations in the same commit.
> >
> >     This way neither 'make coccicheck' nor the static analysis build
> >     job would complain in the topic branch or in the two integration
> >     branches.  And if they do complain, then we would know right away
> >     that they complain because of a well-established semantic patch.
> >     Yet, anyone interested could run 'make coccicheck-pending' to see
> >     where are we heading.
> >
> >   - The author of the "pending" semanting patch should then keep an
> >     eye on already cooking topics: whether any of them contain new
> >     code that should be transformed, and how they progress to
> >     'master', and sending followup patch(es) with the remaining
> >     transformations when applicable.
> >
> >     Futhermore, the author should also pay attention to any new topics
> >     that branch off after the "pending" semantic patch, and whether
> >     any of them introduce code to be transformed, warning their
> >     authors as necessary.
> >
> >   - Finally, after all the dust settled, the dev should follow up with
> >     a patch to:
> >
> >       - promote the "penging" patch to '<name>.cocci', if its purpose
> >         is to avoid undesirable code patterns in the future, or
> >
> >       - remove the semantic patch, if it was used in a one-off
> >         transformation.
> >
> > Thoughts?
> 
> I like the approach of having separate classes of semantic patches:
> (a) the regular "we need to keep checking these" as they address
>     undesirable code patterns, which is what we currently have,
>     and what 'make coccicheck' would complain about.
> (b) The pending patches as you propose. However I would
>     argue that we'd not want to include the transformation into
>     the same patch as then the patch will have merge conflicts.

Since we have a lot of parallel running topics, merge conflicts are basically unavoidable anyway. If the conflicts from the transformation are really that severe, then perhaps the whole series should be postponed to a calmer, more suitable time.

In the case of 'the_repository.cocci', merging its transformations into 'pu' resulted in only four conflicts, and I found all four on the easy side to resolve. I don't think it's worth waiting with the transformations in this particular case.

>     Ideally we'd have an automated process/bot that would apply
>     all pending semantic patches onto master and then checks for
>     conflicts in HEAD..pu, and only sends off the non-conflicting
>     diffs as a topic.

New semantic patches didn't pop up all that frequently in the past, so I'm not sure it's worth investing in such an automation. Of course they can become more frequent in the future, and in that case we might want to reconsider it. Unfortunately, however, Coccinelle's results can't be completely trusted, either because our semantic patches or because Coccinelle itself are buggy...

Show 7 quoted lines
>     Then after a couple integration cycles we'd have all pending
>     changes in, with no conflicts on Junios side.
> 
> So I think we should add a patch like you post, but we would
> need to discuss the exact approach how to deal with pending
> patches. Is it the original dev who should push forward on their
> own pending patches, or does it become a pooled effort?

Well, it makes sense to me that whoever proposes a change with an accompanying new semantic patch should also deal with the necessary followups. However, it doesn't really matter who deals with them, as long as somebody deals with them. I don't think it's much different from e.g. sending a followup bugfix to someone else's patch series.

Previous: Stefan BellerNext: Stefan Beller
Message 36 of 46 in “Bring more repository handles into our code base”
  1. 00/19 Bring more repository handles into our code baseStefan Beller, Oct 16, 2018
  2. 01/19 sha1_file: allow read_object to read objects in arbitrary repositoriesStefan Beller, Oct 16, 2018
  3. 02/19 packfile: allow has_packed_and_bad to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  4. 03/19 object-store: allow read_object_file_extended to read from arbitrary repositoriesStefan Beller, Oct 16, 2018
  5. 04/19 object-store: prepare read_object_file to deal with arbitrary repositoriesStefan Beller, Oct 16, 2018
  6. 05/19 object-store: prepare has_{sha1, object}_file[_with_flags] to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  7. 06/19 object: parse_object to honor its repository argumentStefan Beller, Oct 16, 2018
  8. 07/19 commit: allow parse_commit* to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  9. 08/19 commit-reach.c: allow paint_down_to_common to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  10. 09/19 commit-reach.c: allow merge_bases_many to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  11. 10/19 commit-reach.c: allow remove_redundant to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  12. 11/19 commit-reach.c: allow get_merge_bases_many_0 to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  13. 12/19 commit-reach: prepare get_merge_bases to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  14. 13/19 commit-reach: prepare in_merge_bases[_many] to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  15. 14/19 commit: prepare get_commit_buffer to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  16. 15/19 commit: prepare repo_unuse_commit_buffer to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  17. 16/19 commit: prepare logmsg_reencode to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  18. 17/19 pretty: prepare format_commit_message to handle arbitrary repositoriesStefan Beller, Oct 16, 2018
  19. 18/19 submodule: use submodule repos for object lookupStefan Beller, Oct 16, 2018
  20. Jonathan TanOct 19, 2018
  21. SZEDER GáborOct 25, 2018
  22. Derrick StoleeOct 31, 2018
  23. Stefan BellerNov 1, 2018
  24. 19/19 submodule: don't add submodule as odb for pushStefan Beller, Oct 16, 2018
  25. Jonathan TanOct 19, 2018
  26. Derrick StoleeOct 17, 2018
  27. Stefan BellerOct 17, 2018
  28. 0/2 Bring the_repository into cmd_fooStefan Beller, Oct 18, 2018
  29. 1/2 repository: have get_the_repository() to remove the_repository dependencyStefan Beller, Oct 18, 2018
  30. 2/2 builtin/merge-base.c: do not rely on the_repository any moreStefan Beller, Oct 18, 2018
  31. Jonathan TanOct 18, 2018
  32. Stefan BellerOct 18, 2018
  33. Junio C HamanoOct 19, 2018
  34. New semantic patches vs. in-flight topics [was: Re: [PATCH 00/19] Bring more repository handles into our code base]SZEDER Gábor, Oct 22, 2018
  35. Stefan BellerOct 22, 2018
  36. SZEDER GáborOct 25, 2018
  37. Stefan BellerOct 25, 2018
  38. Junio C HamanoOct 22, 2018
  39. Stefan BellerOct 23, 2018
  40. Junio C HamanoOct 23, 2018
  41. Junio C HamanoOct 23, 2018
  42. Carlo ArenasOct 23, 2018
  43. Junio C HamanoOct 23, 2018
  44. Stefan BellerOct 23, 2018
  45. Junio C HamanoOct 24, 2018
  46. Jeff KingOct 25, 2018

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