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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/65864] New: Consider emitting -Wswitch-bool less aggressively?
Date: Thu, 23 Apr 2015 17:19:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65864

            Bug ID: 65864
           Summary: Consider emitting -Wswitch-bool less aggressively?
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: enhancement
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
                CC: mpolacek at gcc dot gnu.org

Consider the following function from the linux kernel (fs/nfs/nfs4proc.c):

int nfs4_proc_get_rootfh(struct nfs_server *server, struct nfs_fh *fhandle,
                         struct nfs_fsinfo *info,
                         bool auth_probe)
{
        int status;

        switch (auth_probe) {
        case false:
                status = nfs4_lookup_root(server, fhandle, info);
                if (status != -NFS4ERR_WRONGSEC)
                        break;
        default:
                status = nfs4_do_find_root_sec(server, fhandle, info);
        }

        if (status == 0)
                status = nfs4_server_capabilities(server, fhandle);
        if (status == 0)
                status = nfs4_do_fsinfo(server, fhandle, info);

        return nfs4_map_errors(status);
}


The kernel guys have reported that the new -Wswitch-bool warns on this code
and, while ugly, it was a deliberate decision to write it that way (they make
'creative' use of the fall-through in the switch).
I wonder whether it makes sense to restrict the -Wswitch-bool warning to the
cases where the switch condition becomes a boolean from a complex expression
(i.e. a && 0xff, instead of the probably intended a & 0xff)  and not warn when
the switch variable is a simple boolean var.

what do you think?