[PATCH] Warning for main returning a bool.

[Hal Finkel via cfe-commits]

----- Original Message -----
> From: "Aaron Ballman via cfe-commits" <cfe-commits at lists.llvm.org>
> To: "Joshua Hurwitz" <hurwitzj at google.com>
> Cc: "cfe-commits" <cfe-commits at lists.llvm.org>
> Sent: Tuesday, November 15, 2016 12:17:28 PM
> Subject: Re: [PATCH] Warning for main returning a bool.
> 
> On Fri, Oct 14, 2016 at 1:17 PM, Joshua Hurwitz via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
> > See attached.
> >
> > Returning a bool from main is a special case of return type
> > mismatch. The
> > common convention when returning a bool is that 'true' (== 1)
> > indicates
> > success and 'false' (== 0) failure. But since main expects a return
> > value of
> > 0 on success, returning a bool is usually unintended.
> 
> I am not convinced that this is a high-value diagnostic. Returning a
> Boolean from main() may or may not be a bug (the returned value is
> generally a convention more than anything else). Also, why Boolean
> and
> not, say, long long or float?

I've seen this error often enough, but I think we need to be careful about false positives here. I recommend that we check only for explicit uses of boolean immediates (i.e. return true; or return false;) -- these are often bugs.

Aaron, I disagree that the return value is just some kind of convention. It has a clear meaning. Furthermore, the behavior of the system can be quite different for a non-zero exit code than otherwise, and users who don't understand what's going on can find it very difficult to understand what's going wrong.

Thanks again,
Hal

> 
> ~Aaron
> 
> >
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory