Re: [PATCH v2 2/3] docs/misra/rules.rst: add rule 5.5

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 14 Feb 2024, Federico Serafini wrote:
> On 14/02/24 14:15, Jan Beulich wrote:
> > On 14.02.2024 12:27, Federico Serafini wrote:
> > > On 14/02/24 09:28, Jan Beulich wrote:
> > > > On 13.02.2024 23:33, Stefano Stabellini wrote:
> > > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> > > > > ---
> > > > >    docs/misra/rules.rst | 6 ++++++
> > > > >    1 file changed, 6 insertions(+)
> > > > > 
> > > > > diff --git a/docs/misra/rules.rst b/docs/misra/rules.rst
> > > > > index c185366966..931158b354 100644
> > > > > --- a/docs/misra/rules.rst
> > > > > +++ b/docs/misra/rules.rst
> > > > > @@ -181,6 +181,12 @@ maintainers if you want to suggest a change.
> > > > >           headers (xen/include/public/) are allowed to retain longer
> > > > >           identifiers for backward compatibility.
> > > > >    +   * - `Rule 5.5
> > > > > <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_05.c>`_
> > > > > +     - Required
> > > > > +     - Identifiers shall be distinct from macro names
> > > > > +     - Clashes between function-like macros and non-callable entities
> > > > > +       are allowed. The pattern #define x x is also allowed.
> > > > 
> > > > Just for me to know what exactly is covered (hence also a question
> > > > to Roberto as to [to be] implemented Eclair behavior): Even when
> > > > the above would be sufficient (and imo better) people frequently
> > > > write
> > > > 
> > > > #define a(x, y) b(x, y)
> > > > 
> > > > which, transformed to the specific case here, would then be
> > > > 
> > > > #define a(x, y) a(x, y)
> > > > 
> > > > I'd assume such ought to also be covered, but that's not clear
> > > > from the spelling above.
> > > 
> > > I list what happens in some different situations,
> > > then we can find the right words for the documentation and/or
> > > refine the configuration:
> > > 
> > > If you
> > > #define x x
> > > and then use `x' as identifier,
> > > the resulting violation is deviated (allowed pattern).
> > > 
> > > If you
> > > #define a(x, y) a(x, y)
> > > and then use `a' as identifier for a non-callable entity,
> > > the resulting violation is deviated (no clash with non-callable
> > > entities).
> > > If you use identifier `a' for a callable entity, the resulting violation
> > > is reported: the allowed pattern covers only macros expanding to their
> > > own name, in this case the macro name is considered to be
> > > `a' only, not a(x, y).
> > > 
> > > If you
> > > #define a(x, y) b(x, y)
> > > and then use `a' as identifier for a non-callable entity,
> > > the resulting violation is deviated (no clash with non-callable
> > > entities).
> > 
> > I'm afraid I don't see what violation there is in this case, to
> > deviate. As a result I'm also not sure I correctly understand the
> > rest of your reply.
> 
> #define a(x, y) b(x, y)
> 
> int a; // Violation of Rule 5.5.
> 
> The macro name `a' that exist before the preprocessing phase,
> still exists after the preprocessing phase as identifier for the integer
> variable and this is a violation.
> 
> > > If you use `a' as identifier for a callable entity,
> > > this is not a violation because after the preprocessing phase,
> > > identifier `a' no longer exists.
> I correct myself:
> if you use `a' as identifier for a *function*,
> it is not a violation because after the preprocessing phase
> the identifier `a' no longer exists, for example:
> 
> #define a(x, y) b(x, y)
> 
> void a(int x, int y); // Ok.

Federico, do you have a better wording suggestion for this rule?

Jan, any further requests here? What would you like to see as next step?