Re: [PATCH] ci: update 'static-analysis' to Ubuntu 22.04

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Fri, Aug 26, 2022 at 09:46:54AM -0700, Junio C Hamano wrote:
> Jeff King <peff@peff.net> writes:
> 
> >> But the fix here isn't to delete unused.cocci, but to hold off on the
> >> UNUSEwork D() patches until we figure out how to make coccinelle jive with
> >> them.
> >
> > Yeah, my general skepticism and disappointment above notwithstanding,
> > this seems like the best path forward from here. I tried a few other
> > tricks (like --macro-file and --iso-file), but if its parser chokes, I
> > don't think there's much we can do about it. Even if we wrote a patch to
> > coccinelle itself (and I have no interest in doing that myself), it
> > would take a while to become available.
> 
> If it is just a single unused.cocci, I would actually think removing
> it would be a much better path forward.  UNUSED() that renames to
> help folks without checking compilers would help noticing bad code
> much earlier than unused.cocci many contributors are not running
> themselves anyway.

Here is another reason for the removal of 'unused.cocci': it's very
costly to apply that semantic patch to the whole code base.

  make SPATCH_BATCH_SIZE=32 contrib/coccinelle/unused.cocci.patch

takes 440s on my machine, whereas the second slowest 'object_id.cocci'
takes only 56s [1].  Applying 'unused.cocci' to some of our source files
individually takes well over a minute:

  $ time spatch --all-includes --sp-file contrib/coccinelle/unused.cocci builtin/log.c
  warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
  warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
  HANDLING: builtin/log.c
  Note: processing took    83.1s: builtin/log.c
  
  real	1m23.083s
  user	1m22.983s
  sys	0m0.033s
  $ time spatch --all-includes --sp-file contrib/coccinelle/unused.cocci builtin/rebase.c 
  warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
  warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
  HANDLING: builtin/rebase.c
  Note: processing took    83.2s: builtin/rebase.c
  
  real	1m23.223s
  user	1m23.156s
  sys	0m0.017s

In my opinion the benefits of having 'unused.cocci' clearly do not
justify the costs.

[1] https://public-inbox.org/git/20220824113901.GD1735@szeder.dev/