[Cocci] Replacing one (specific!) type with another

[Nikolaus@rath.org (Nikolaus Rath)]

On Oct 06 2016, Julia Lawall <julia.lawall@lip6.fr> wrote:
>> Somehow I'm having a really hard time grasping the fundamentals. The
>> first two examples make sense - I could adapt them for similar
>> situations. But then, I still have absolutely no idea how I would come
>> up with the third example, or how to adapt it. What does "idexpression"
>> mean? What does "ptr at p1" mean? Is this documented anywhere?
>
> idexpression is an expression that is resricted to be an identifier.  It
> allows you to put a type on an expression that has the form of an
> identifier.  You can also say identifier x;  But that is just a name.  It
> has no type.  It could be an expression, a field name, a parameter name,
> etc.

Hm. Based on your last two sentences I'd conclude that 'idexpression'
matches variable names for variables of a specific type. But that
doesn't seem to be what you describe in your first two sentences. Could
you explain what you meant iwth "expression that has the form of an
identifier"?

To me, an identifier is something that's written literally into the
source code and cannot be meaningfully taken apart, e.g. a function
name, variable name, or the member of a struct. An expression, on the
other hand, is something that can be meaningfully split into
sub-components. Is that also how you use these terms?

> @ connects patterns that match the same term.  So match a term against the
> explicit name ptr and also match it against an identifier expression that
> has a particular type.  This is not exactly a beginner example.

Okay, I'll just ignore that for now.

>> I'd hate to waste your time asking tons of such trivial questions on the
>> mailing list, but I just can't find any helpful documentation at all...
>
> If you look on the web page in the papers and slides section, at the top
> there are several tutorials and overview talks, some with video.

I think I looked at everything that is not a video. But none of it
mentioned that you can put an arbitrary name between the @@ or explained
what the different metavariable types (idexpression, expression, etc)
are.

Anyway, enough whining. Coccinelle seems like a really useful tool, even
if I'm having an impedance mismatch with its documentation.


Best,
-Niko

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