Re: [cocci] [PATCH] add usage-strings ci check and amend remaining usage strings

[Julia Lawall <julia.lawall@inria.fr>]

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On Fri, 25 Feb 2022, Johannes Schindelin wrote:

> Hi Julia,
>
> On Tue, 22 Feb 2022, Julia Lawall wrote:
>
> > [I]f there are some cases that are useful to do statically, with only
> > local information, then using Coccinelle could be useful to get the
> > problem out of the way once and for all.  Coccinelle doesn't support
> > much processing of strings directly, but you can always write some
> > python code to test the contents of a string and to create a new one.
> >
> > Let me know if you want to try this.  You can also check, eg the demo
> > demos/pythontococci.cocci to see how to create code in a python script and
> > then use it in a normal SmPL rule.
> >
> > If some context has to be taken into account and the context in the same
> > function, then that can also be done with Coccinelle, eg
> >
> > A
> > ...
> > B
> >
> > matches the case where after an A there is a B on all execution paths
> > (except perhaps those that end in an error exit) and
> >
> > A
> > ... when exists
> > B
> >
> > matches the case where there is a B sometime after executing A, even if
> > that does not always occur.
> >
> > If the context that you are interested in is in a called function or is in
> > the calling context, then Coccinelle might not be the ideal choice.
> > Coccinelle works on one function at a time, so to do anything
> > interprocedural, you have to do some hacks.
>
> Right. The code in question is not actually calling a function, but a
> macro, and passes a literal string to the macro that we would want to
> check statically.

Coccinelle doesn't care about whether a function is called or whether a
macro is called.  It considers everything to be a function.

>
> I did have my doubts that it would be easy with Coccinelle, but since Ævar
> seemed so confident, I tried it, struggled, and decided to follow up with
> you.

Something like this:

@r1@
expression e;
@@

N(e)

@script:python s@
e << r1.e;
replacement;
@@

if string_ok e
then cocci.include_match(False)
else coccinelle.replacement = "\"better string\""

@@
expression r1.e;
expression s.replacement;
@@
- N(e)
+ N(replacement)

------------------

You can fill in the definition of string_ok and better string.  I think
the \" will be necessary, because the value of an expression metavariable
at the python level is a string, so there should be a string inside of it
to make it a string expression.

julia