Re: Error compiling bison 3.4.2 on Solaris

[Paul Eggert]

On 10/20/19 5:04 AM, Akim Demaille wrote:

> I still believe the warning is valid.  Annoying, but valid.

Sure, just as a compiler that said "warning: semicolon present in the source 
code" for each semicolon would be annoying-but-valid. (Semicolons are dangerous! 
Think how much safer your C program will be if you omit semicolons! :-)

However, the question is not whether the warning is *valid*; it's whether the 
warning is *useful*. And when the warning is about code that is doing portable 
and reliable integer overflow checking (as is the case here), a compiler that in 
essence is saying "watch out! the code is trying to do portable and reliable 
integer overflow checking!" is harmful, not useful.

> And therefore I would prefer to have intprops.h use pragmas to disable it 
> locally.

I'd rather not. Newer compilers are doing their jobs better in this area, and we 
should not worry about pacifying older compilers as it's considerably more 
trouble than it's worth. Instead, we should simply suggest that builders who 
employ older or buggy compilers should not use --enable-gcc-warnings.

> But of course we can disable the warning for bison, and not the test suite, as 
> below.  It fixes the issues with GCC, but not yet with old clangs (3.3 and 3.4).

Yes, that is a good fix - it's more targeted than the one I proposed.

To pacify old Clangs, you can add 
"-Wno-tautological-constant-out-of-range-compare" as well. That's what Coreutils 
does.

To give you a preview of future problems you might run into with Clang, here are 
some other Clang flags that Coreutils and other GCC projects have found useful:

-Wno-tautological-compare
-Wno-switch
-Wno-pointer-sign
-Wno-string-plus-int
-Wno-unknown-attributes
-Wno-initializer-overrides

Emacs also adds "-Wno-null-pointer-arithmetic" on the somewhat-controversial 
grounds that ((char *)0 == (char *)0 + 0) is true everywhere even if the C 
standard doesn't require it (Emacs relies on this for its pointer tagging).

Of course Bison should add these other flags only if needed.