Subject: Re: [PATCH] mailinfo: resolve -Wstring-plus-int warning

From: Jeff King <[email-masked]>
Date: Tue, 23 Sep 2014 02:04:07 -0400

On Mon, Sep 22, 2014 at 05:10:08PM -0400, Eric Sunshine wrote:

> On Mon, Sep 22, 2014 at 1:41 PM, Junio C Hamano <[email-masked]> wrote:
> > Eric Sunshine <[email-masked]> writes:
> >
> >> The just-released Apple Xcode 6.0.1 has -Wstring-plus-int enabled by
> >> default which complains about pointer arithmetic applied to a string
> >> literal:
> >>
> >>     builtin/mailinfo.c:303:24: warning:
> >>         adding 'long' to a string does not append to the string
> >>             return !memcmp(SAMPLE + (cp - line), cp, strlen(SAMPLE) ...
> >>                            ~~~~~~~^~~~~~~~~~~~~
> >
> > And why is that a warning-worthy violation?
> 
> Not being privy to Apple's decision making process, I can only guess
> that it is in response to their new Swift programming language which
> they are pushing heavily on iOS (and soon Mac OS X), in which '+' is
> the string concatenation operator. For projects written in Swift and
> incorporating legacy or portable components in C, C++, or Objective-C,
> the warning may help programmer's avoid the pitfall of thinking that
> '+' is also concatenation in the C-based languages.

That is my reading from the warning text, too, but I have to wonder:
wouldn't that mean they should be warning about pointer + pointer, not
pointer + int?

Also, wouldn't the same advice apply to adding to _any_ char pointer,
not just a string literal?

I know you don't have answers to those questions, but the whole thing
seems rather silly to me.

> > Can we have them fix their compiler instead?
> 
> If the above supposition is correct, then it's likely that Apple
> considers this a feature, not a bug which needs to be fixed.

I don't mind silencing this one warning (even though I find it a little
ridiculous). I'm slightly concerned that more brain-damage may be coming
our way, but we can deal with that if it ever does.

Like Junio, I prefer keeping strlen() rather than switching to sizeof,
as it is less error-prone (no need for extra "-1" dance, and it won't
silently do the wrong thing if the array is ever converted to a
pointer).

-Peff