Re: C/C++ PATCH to implement -Wmultistatement-macros (PR c/80116)

[Marek Polacek <polacek@redhat.com>]

On Sat, Jun 10, 2017 at 12:03:18AM +0200, Gerald Pfeifer wrote:
> On Thu, 8 Jun 2017, David Malcolm wrote:
> > How about:
> > 
> > "Warn about unsafe multiple statement macros that appear to be guarded
> > by a clause such as if, else, while, or for, in which only the first
> > statement is actually guarded after the macro is expanded."
> > 
> > or somesuch?
> 
> Yes, I like this.
> 
> On Thu, 8 Jun 2017, Martin Sebor wrote:
> > I don't have strong feelings about the current wording but if it
> > should be tweaked for accuracy I would suggest to use the formal
> > term "controlling expression", similarly to -Wswitch-unreachable.
> 
> That sounds good to me.
> 
> Some comments on the original patch:
> 
>   +Warn about macros expanding to multiple statements in a body of a conditional,
>   +such as @code{if}, @code{else}, @code{for}, or @code{while}.
> 
> "in the body of a $WHATEVER_WE_SHALL_CALL_IT"
 
It now says something other than that, so that mistake is not there anymore.

>   +The can usually be fixed by wrapping the macro in a do-while loop:
> 
> Is there a particular reason for not using an if(1) { } statement?
> 
> Ah, of course, a following else statement would be impacted by that.
> Do we want to note that in the documentation?

I don't think so, we only suggest do {} while (0);.

>   +This warning is enabled by @option{-Wall} in C and C++.
> 
> "for C and C++" instead of "in"?

Other parts of invoke.text use both, so I left that as it was.  I think
both work here.

> I'm curious to see how many issues this is going to find in real-world
> code out there!

Yeah, me too.

	Marek