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

[mstefani@redhat.com (Michael Stefaniuc)]

On 10/05/2016 06:09 PM, Nikolaus Rath wrote:
> On Oct 05 2016, Julia Lawall <julia.lawall@lip6.fr> wrote:
>> On Tue, 4 Oct 2016, Nikolaus Rath wrote:
>>
>>> Hello,
>>>
>>> In a set of C files, I would like to replace each instance of one type
>>> (struct fasel_foo) with another type (struct fasel_bar). For instance,
>>>
>>> char* fasel_foo_print(struct fasel_foo *ptr) {
>>>     // ...
>>>    return "this struct fasel_foo string should not change";
>>> }
>>>
>>> should become
>>>
>>> char* fasel_foo_print(struct fasel_bar *ptr) {
>>>     // ...
>>>    return "this struct fasel_foo string should not change";
>>> }
>>>
>>>
>>> Based on the LWN articles that I've read, this seems like the perfect
>>> use-case for coccinelle. However, somehow I'm struggling to write a
>>> patch for this. All the documentation that I could get my hands on seems
>>> to describe more abstract changes that require the use of variables -
>>> but as far as I can tell, I need something much simpler:
>>>
>>> @@
>>> "struct fasel_foo must be a type name!"
>>> @@
>>> - struct fasel_foo
>>> + struct fasel_bar
>>>
>>>
>>> ...if only I knew what to put between the @@.
>>
>> Put nothing :)  From the word struct it should figure out that it is
>> working on a type.
> 
> Oh, great! Thanks!
> 
> 
> This solves my problem, but it makes me wonder how this generalizes to
> other problems. For example, 
> 
> 1. What would I need to do if I don't want to replace a struct but
>    something typedef'd? (my_type *ptr --> new_type *ptr).
Easy

@@
typedef my_type, new_type;
@@
- my_type
+ new_type

> 2. ..and how would I go about if instead of the type, I want to replace
>    a variable name? (my_type *ptr --> my_type *pointer).
Depends on the exact circumstance. But that's easy to figure out. I
recommend the workshop papers and tutorials from
http://coccinelle.lip6.fr/papers.php; I wish I would have had those when
I started with coccinelle.

bye
	michael