Re: [PATCH v2] config: avoid "write_in_full(fd, buf, len) < len" pattern

[Ramsay Jones <ramsay@ramsayjones.plus.com>]

On 13/09/17 23:43, Ramsay Jones wrote:
> 
> 
> On 13/09/17 19:58, Jeff King wrote:
>> On Wed, Sep 13, 2017 at 11:24:31AM -0700, Jonathan Nieder wrote:
>>
>>> For what it's worth,
>>> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
>>
>> Thanks, and thank you for questioning the ptrdiff_t bits that didn't
>> make sense. I _thought_ they felt like nonsense, but couldn't quite
>> puzzle it out.
>>
>>> Compilers' signed/unsigned comparison warning can be noisy, but I'm
>>> starting to feel it's worth the suppression noise to turn it on when
>>> DEVELOPER=1 anyway.  What do you think?  Is there a way to turn it on
>>> selectively for certain functions on the LHS (like read() and write()
>>> style functions)?
>>
>> Obviously we couldn't turn them on for -Werror at this point. Let me see
>> how bad "-Wsign-compare -Wno-error=sign-compare" is.
>>
>>   $ make 2>&1 | grep -c warning:
>>   1391
>>
>> Ouch. I'm afraid that's probably not going to be very helpful. Even if I
>> were introducing a new problem, I'm not likely to see it amidst the mass
>> of existing complaints.
> 
> Hmm, about three or four years ago, I spent two or three evenings
> getting git to compile -Wextra clean. I remember the signed/unsigned
> issue was the cause of a large portion of the warnings issued by
> the compiler. I was surprised that it took such a relatively short
> time to do. However, it affected quite a large portion of the code, so
> I didn't think Junio would even consider applying it. Also, I only used
> gcc and was anticipating having additional warnings on clang (but I
> didn't get around to trying).
> 
> Maybe I should give it another go. :-D

For example, I remember the patch given below reduced the number
of warnings quite a bit (because it's an inline function in a
header file).

I just tried it again tonight; the current master branch has 3532
warnings when compiled with -Wextra, 1409 of which are -Wsign-compare
warnings. After applying the patch below, those numbers are reduced
by 344 to 3188/1065.

Still quite a bit to go ... ;-)

ATB,
Ramsay Jones

-- >8 --
Subject: [PATCH] git-compat-util: avoid -Wsign-compare warnings from xsize_t()

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
---
 git-compat-util.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index 6678b488c..2f3cf0883 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -898,9 +898,11 @@ static inline char *xstrdup_or_null(const char *str)
 
 static inline size_t xsize_t(off_t len)
 {
-	if (len > (size_t) len)
+	size_t size = (size_t) len;
+
+	if (len != (off_t) size)
 		die("Cannot handle files this big");
-	return (size_t)len;
+	return size;
 }
 
 __attribute__((format (printf, 3, 4)))
-- 
2.14.0