Implement -Wimplicit-fallthrough (version 9)

[Segher Boessenkool]

On Tue, Sep 27, 2016 at 01:31:15PM +0200, Jakub Jelinek wrote:
> I think it is important to think in terms of what regexps we still want to
> match, even when the matching is actually implemented in C, not using
> regexps.  And yes, you list one reason why arbitrary text with fall and
> through somewhere in it is not a good idea.  Another:
> /* XXX Really fallthru?  */
> (what we have in pch.c).
> So, if you want to allow ... fall through ... and else fall through, and
> perhaps // fall through - some explanation
> then it might be e.g.
> //-fallthrough$
> //@fallthrough@$
> /\*-fallthrough\*/
> /\*@fallthrough@\*/
> //[ \t.]*(ELSE )?FALL(S | |-)?THR(OUGH|U)[ \t.]*(-.*)?$
> //[ \t.]*(Else )?Fall(s | |-)?[Tt]hr(ough|u)[ \t.]*(-.*)?$
> //[ \t.]*(else )?fall(s | |-)?thr(ough|u)[ \t.]*(-.*)?$
> /\*[ \t.]*(ELSE )?FALL(S | |-)?THR(OUGH|U)[ \t.]*(-.*)?\*/
> /\*[ \t.]*(Else )?Fall(s | |-)?[Tt]hr(ough|u)[ \t.]*(-.*)?\*/
> /\*[ \t.]*(else )?fall(s | |-)?thr(ough|u)[ \t.]*(-.*)?\*/
> where . would match even newlines in the last 3,
> but $ would always match just end of line?

Any comment with text

^[^_[:alnum:]]*(else )?fall(s | |-)?thr(ough|u)[^_[:alnum:]]*$

perhaps?  Case-insensitive.  Or allow any amount of space, or even any
interpunction.  Just don't allow any alphanumerics except for those
exact words, and there won't be many false hits at all.


Segher