Re: [HACKERS] Re: [PATCH] Compile without warning with gcc's -Wtype-limits, -Wempty-body

2013-01-16 Thread Peter Eisentraut 
On 1/15/13 6:36 AM, Andres Freund wrote:
 I just think that the price of fixing a single Assert() that hasn't
 changed in years where the variable isn't likely to ever get signed is
 acceptable.

Well, once you get past that one change you proposed, you will also find

pg_standby.c: In function 'SetWALFileNameForCleanup':
pg_standby.c:348:3: error: comparison of unsigned expression = 0 is
always true [-Werror=type-limits]

(which, curiously, is the only one that clang complains about).

I don't like removing safety checks from code when there is no other
mechanism that could make up for it somehow.

I think the best practice at the moment, as with most gcc -Wextra
warnings, is to manually check them once in a while.



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[HACKERS] Re: [PATCH] Compile without warning with gcc's -Wtype-limits, -Wempty-body

2013-01-15 Thread Andres Freund 
On 2013-01-14 22:26:39 -0500, Tom Lane wrote:
 Andres Freund and...@2ndquadrant.com writes:
  On 2013-01-14 20:39:05 -0500, Peter Eisentraut wrote:
  On Tue, 2013-01-15 at 00:29 +0100, Andres Freund wrote:
  Independently from this patch, should we add -Wtype-limits to the
  default parameters?
 
  I think we have had a discussion along this line before.  I am against
  fixing warnings from this option, because those changes would hide
  errors if a variable's type changed from signed to unsigned or vice
  versa, which could happen because of refactoring or it might be
  dependent on system headers.
 
  Well, I already found a bug (although with very limited consequences) in
  the walsender code and one with graver consequences in code I just
  submitted. So I don't really see that being on-par with some potential
  future refactoring...
 
 FWIW, I agree with Peter --- in particular, warning against x = MIN
 just because MIN happens to be zero and x happens to be unsigned is the
 sort of nonsense up with which we should not put.  Kowtowing to that
 kind of warning makes the code less robust, not more so.

Oh, I agree, that warning is pointless in itself.

But in general doing a comparison like  0 *can* show a programming
error as evidenced e.g. by
http://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3f4b1749a8168893558f70021be4f40c650bbada
and just about the same error I made in xlogdump.

I just think that the price of fixing a single Assert() that hasn't
changed in years where the variable isn't likely to ever get signed is
acceptable.

 It's a shame that the compiler writers have not figured this out and
 separated misguided pedantry from actually-useful warnings.  If I assign
 -1 to an unsigned variable, by all means tell me about *that*.  Don't
 tell me your opinion of whether an assertion check is necessary.

Yea, but I have to admit its damned hard hard to automatically discern
the above actually valid warning and the bogus Assert...

Greetings,

Andres Freund

-- 
 Andres Freund http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training  Services


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