[Bug c++/60978] -Wenum-compare warns too eagerly

["jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60978

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |paolo.carlini at oracle dot com

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #5)
> I think it should not warn for anonymous enums. The point of the warning is
> that using different enum types in a conditional expression is often some
> programming mistake. But in the case of anonymous enums, they are probably
> just used as named constants, so there is no much point in warning.

I don't think I agree.  Even with anonymous enums there is the risk that, as in
the reduced testcase here, you end up returning the same value by different
names.

You shouldn't get the warning about IPPROTO_ICMP vs IPPROTO_ICMPV66, as they
are members of the same anonymous enum.  If 4.9 started complaining, that's the
bug.
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From: "ppluzhnikov at google dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/60978] -Wenum-compare warns too eagerly
Date: Tue, 02 Dec 2014 22:11:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id`978

--- Comment #9 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
(In reply to Jason Merrill from comment #8)

> You shouldn't get the warning about IPPROTO_ICMP vs IPPROTO_ICMPV66, as they
> are members of the same anonymous enum.

They are?

In glibc-2.19, include/netinet/in.h:


/* Standard well-defined IP protocols.  */
enum
  {
    IPPROTO_IP = 0,       /* Dummy protocol for TCP.  */
#define IPPROTO_IP        IPPROTO_IP
    IPPROTO_ICMP = 1,       /* Internet Control Message Protocol.  */
#define IPPROTO_ICMP        IPPROTO_ICMP
...
};

/* If __USE_KERNEL_IPV6_DEFS is defined then the user has included the kernel
   network headers first and we should use those ABI-identical definitions
   instead of our own.  */
#ifndef __USE_KERNEL_IPV6_DEFS
enum
  {
    IPPROTO_HOPOPTS = 0,   /* IPv6 Hop-by-Hop options.  */
...
    IPPROTO_ICMPV6 = 58,   /* ICMPv6.  */
...
};


Looks like different anonymous enums to me.