4d168e742a
Sometimes we want to suppress a coccinelle transformation
inside a particular function. For example, in finding
conversions of hashcmp() to oidcmp(), we should not convert
the call in oidcmp() itself, since that would cause infinite
recursion. We write that like this:
@@
identifier f != oidcmp;
expression E1, E2;
@@
f(...) {...
- hashcmp(E1->hash, E2->hash)
+ oidcmp(E1, E2)
...}
to match the interior of any function _except_ oidcmp().
Unfortunately, this doesn't catch all cases (e.g., the one
in sequencer.c that this patch fixes). The problem, as
explained by one of the Coccinelle developers in [1], is:
For transformation, A ... B requires that B occur on every
execution path starting with A, unless that execution path
ends up in error handling code. (eg, if (...) { ...
return; }). Here your A is the start of the function. So
you need a call to hashcmp on every path through the
function, which fails when you add ifs.
[...]
Another issue with A ... B is that by default A and B
should not appear in the matched region. So your original
rule matches only the case where every execution path
contains exactly one call to hashcmp, not more than one.
One way to solve this is to put the pattern inside an
angle-bracket pattern like "<... P ...>", which allows zero
or more matches of P. That works (and is what this patch
does), but it has one drawback: it matches more than we care
about, and Coccinelle uses extra CPU. Here are timings for
"make coccicheck" before and after this patch:
[before]
real 1m27.122s
user 7m34.451s
sys 0m37.330s
[after]
real 2m18.040s
user 10m58.310s
sys 0m41.549s
That's not ideal, but it's more important for this to be
correct than to be fast. And coccicheck is already fairly
slow (and people don't run it for every single patch). So
it's an acceptable tradeoff.
There _is_ a better way to do it, which is to record the
position at which we find hashcmp(), and then check it
against the forbidden function list. Like:
@@
position p : script:python() { p[0].current_element != "oidcmp" };
expression E1,E2;
@@
- hashcmp@p(E1->hash, E2->hash)
+ oidcmp(E1, E2)
This is only a little slower than the current code, and does
the right thing in all cases. Unfortunately, not all builds
of Coccinelle include python support (including the ones in
Debian). Requiring it may mean that fewer people can easily
run the tool, which is worse than it simply being a little
slower.
We may want to revisit this decision in the future if:
- builds with python become more common
- we find more uses for python support that tip the
cost-benefit analysis
But for now this patch sticks with the angle-bracket
solution, and converts all existing cocci patches. This
fixes only one missed case in the current code, though it
makes a much better difference for some new rules I'm adding
(converting "!hashcmp()" to "hasheq()" misses over half the
possible conversions using the old form).
[1] https://public-inbox.org/git/alpine.DEB.2.21.1808240652370.2344@hadrien/
Helped-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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| buildsystems | ||
| coccinelle | ||
| completion | ||
| contacts | ||
| credential | ||
| diff-highlight | ||
| emacs | ||
| examples | ||
| fast-import | ||
| git-jump | ||
| git-shell-commands | ||
| hg-to-git | ||
| hooks | ||
| long-running-filter | ||
| mw-to-git | ||
| persistent-https | ||
| remote-helpers | ||
| stats | ||
| subtree | ||
| svn-fe | ||
| thunderbird-patch-inline | ||
| update-unicode | ||
| vscode | ||
| workdir | ||
| git-resurrect.sh | ||
| README | ||
| remotes2config.sh | ||
| rerere-train.sh | ||
Contributed Software Although these pieces are available as part of the official git source tree, they are in somewhat different status. The intention is to keep interesting tools around git here, maybe even experimental ones, to give users an easier access to them, and to give tools wider exposure, so that they can be improved faster. I am not expecting to touch these myself that much. As far as my day-to-day operation is concerned, these subdirectories are owned by their respective primary authors. I am willing to help if users of these components and the contrib/ subtree "owners" have technical/design issues to resolve, but the initiative to fix and/or enhance things _must_ be on the side of the subtree owners. IOW, I won't be actively looking for bugs and rooms for enhancements in them as the git maintainer -- I may only do so just as one of the users when I want to scratch my own itch. If you have patches to things in contrib/ area, the patch should be first sent to the primary author, and then the primary author should ack and forward it to me (git pull request is nicer). This is the same way as how I have been treating gitk, and to a lesser degree various foreign SCM interfaces, so you know the drill. I expect that things that start their life in the contrib/ area to graduate out of contrib/ once they mature, either by becoming projects on their own, or moving to the toplevel directory. On the other hand, I expect I'll be proposing removal of disused and inactive ones from time to time. If you have new things to add to this area, please first propose it on the git mailing list, and after a list discussion proves there are some general interests (it does not have to be a list-wide consensus for a tool targeted to a relatively narrow audience -- for example I do not work with projects whose upstream is svn, so I have no use for git-svn myself, but it is of general interest for people who need to interoperate with SVN repositories in a way git-svn works better than git-svnimport), submit a patch to create a subdirectory of contrib/ and put your stuff there. -jc