[Cocci] Newline escape in preprocessor

[Cocci] Newline escape in preprocessor

[Mansour Moufid]

Hi,

I'd like to add a statement after another within a preprocessor
expression, but spatch adds the line without an escape (backslash).

x.c:

    #define X(a) x(a);

(I know the above is not technically correct but it's super common.)

x.cocci:

    @@
    expression e;
    @@
        x(e);
    +   y(e);

output:

    $ spatch --sp-file x.cocci x.c
    HANDLING: x.c
    diff =
    --- x.c
    +++ /tmp/cocci-output-80658-7f90b1-x.c
    @@ -1 +1,2 @@
     #define X(a) x(a);
    +y(a);

I can think of two solutions, if an expression is inside a
preprocessor statement: add a backslash before every newline, or skip
the newline.
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Re: [Cocci] Newline escape in preprocessor

[Julia Lawall]

On Thu, 22 Oct 2020, Mansour Moufid wrote:

> Hi,
>
> I'd like to add a statement after another within a preprocessor
> expression, but spatch adds the line without an escape (backslash).
>
> x.c:
>
>     #define X(a) x(a);
>
> (I know the above is not technically correct but it's super common.)
>
> x.cocci:
>
>     @@
>     expression e;
>     @@
>         x(e);
>     +   y(e);
>
> output:
>
>     $ spatch --sp-file x.cocci x.c
>     HANDLING: x.c
>     diff =
>     --- x.c
>     +++ /tmp/cocci-output-80658-7f90b1-x.c
>     @@ -1 +1,2 @@
>      #define X(a) x(a);
>     +y(a);
>
> I can think of two solutions, if an expression is inside a
> preprocessor statement: add a backslash before every newline, or skip
> the newline.

Indeed Coccinelle is not aware that the added code is within a #define.
Maybe it is easy to add that.

Thanks for the report.

julia
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Re: [Cocci] Adjusting replacement lists with SmPL?

[Markus Elfring]

> I'd like to add a statement after another within a preprocessor expression,

How do you think about to refer to a “#define directive”?


> but spatch adds the line without an escape (backslash).

I imagine that we stumble on another target conflict here.
https://github.com/coccinelle/coccinelle/issues/139

Do you really want to adjust a bit of text according to a preprocessing definition?


>     #define X(a) x(a);
>
> (I know the above is not technically correct but it's super common.)

I stumble on understanding difficulties for this information.
Would you like to clarify the knowledge about correctness a bit more?


>     @@
>     expression e;
>     @@
>         x(e);
>     +   y(e);

How should the scope be specified that a change should be performed
only for preprocessor code (replacement lists for your transformation approach)?


> I can think of two solutions, if an expression is inside a
> preprocessor statement: add a backslash before every newline, or skip
> the newline.

Would you like to choose the preferred coding style for such an use case?

Regards,
Markus
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Re: [Cocci] Adjusting replacement lists with SmPL?

[Julia Lawall]

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On Fri, 23 Oct 2020, Markus Elfring wrote:

> > I'd like to add a statement after another within a preprocessor expression,
> >
> > How do you think about to refer to a “#define directive”?
> >
> >
> > > but spatch adds the line without an escape (backslash).
> >
> > I imagine that we stumble on another target conflict here.
> > https://github.com/coccinelle/coccinelle/issues/139
> >
> > Do you really want to adjust a bit of text according to a preprocessing
> > definition?
> >
> >
> > >     #define X(a) x(a);
> > >
> > > (I know the above is not technically correct but it's super common.)
> >
> > I stumble on understanding difficulties for this information.
> > Would you like to clarify the knowledge about correctness a bit more?
> >
> >
> > >     @@
> > >     expression e;
> > >     @@
> > >         x(e);
> > >     +   y(e);
> >
> > How should the scope be specified that a change should be performed
> > only for preprocessor code (replacement lists for your transformation
> > approach)?

I don't think he is asking that.  He means, if the call to x happens to be
in a macro definition, how can he ensure that the transformed code treats
newlines in the right way.

julia


> >
> >
> > > I can think of two solutions, if an expression is inside a
> > > preprocessor statement: add a backslash before every newline, or skip
> > > the newline.
> >
> > Would you like to choose the preferred coding style for such an use case?
> >
> > Regards,
> > Markus
> > _______________________________________________
> > Cocci mailing list
> > Cocci@systeme.lip6.fr
> > https://systeme.lip6.fr/mailman/listinfo/cocci
> >

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Re: [Cocci] Adjusting replacement lists with SmPL?

[Mansour Moufid]

On Fri, Oct 23, 2020 at 11:00 AM Markus Elfring <Markus.Elfring@web.de> wrote:
>
> > I'd like to add a statement after another within a preprocessor expression,
>
> How do you think about to refer to a “#define directive”?

I mean, not specifically in the #define, but anywhere.

(I don't try to patch preprocessor directives with spatch, I use sed for that.)

> >     #define X(a) x(a);
> >
> > (I know the above is not technically correct but it's super common.)
>
> I stumble on understanding difficulties for this information.
> Would you like to clarify the knowledge about correctness a bit more?

A trailing colon in a #define leads to code like this:

    {
        X(1)
        X(2)
        ...
    }

... which of course does not parse.  It would be better to use a do {
... } while (0), or better yet an inline function.  But unfortunately
the above style is very common.

On Fri, Oct 23, 2020 at 11:11 AM Julia Lawall <julia.lawall@inria.fr> wrote:

> I don't think he is asking that.  He means, if the call to x happens to be
> in a macro definition, how can he ensure that the transformed code treats
> newlines in the right way.

Yes, exactly. :)
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