[gcc r16-7450] libstdc++: Fix std::regex_traits::lookup_classname [PR124015]

[Jonathan Wakely]

https://gcc.gnu.org/g:49d219a5d7a8ad570992a4065268b58a581b7d9f

commit r16-7450-g49d219a5d7a8ad570992a4065268b58a581b7d9f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Feb 5 17:32:23 2026 +0000

    libstdc++: Fix std::regex_traits::lookup_classname [PR124015]
    
    This fixes a bug in regex_traits::lookup_classname(f, l, true) where the
    result was always ctype_base::alpha for any input sequence [f, l) that
    has the ctype_base::lower or ctype_base::upper bits set. For targets
    that define alpha as lower|upper (rather than having a distinct bit for
    alpha) this bug meant that all masks which have lower or upper bits set
    were replaced with alpha when the icase parameter is true. This has the
    effect that trying to do a case insensitive match for [:alnum:],
    [:graph:], or [:print:] was equivalent to matching [:alpha:] instead,
    which is obviously not correct.
    
    Based on inspection of the ctype_base.h files under the config/os
    directory, the bug appears to affect newlib, picolibc, qnx and vxworks.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/124015
            * include/bits/regex.tcc (regex_traits::lookup_classname): Fix
            handling of icase parameter.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/regex.tcc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/regex.tcc b/libstdc++-v3/include/bits/regex.tcc
index ca500d21c348..7715d653df5d 100644
--- a/libstdc++-v3/include/bits/regex.tcc
+++ b/libstdc++-v3/include/bits/regex.tcc
@@ -302,8 +302,8 @@ namespace __detail
 	if (__s == __it.first)
 	  {
 	    if (__icase
-		&& ((__it.second
-		     & (ctype_base::lower | ctype_base::upper)) != 0))
+		&& (__it.second._M_base == ctype_base::lower
+		      || __it.second._M_base == ctype_base::upper))
 	      return ctype_base::alpha;
 	    return __it.second;
 	  }