[gcc r16-5875] libstdc++: Fix pretty printer lookup for class templates [PR122812]

[Jonathan Wakely]

https://gcc.gnu.org/g:dce0d564d742617f71297c88e4a1c0d6038f2c47

commit r16-5875-gdce0d564d742617f71297c88e4a1c0d6038f2c47
Author: Vladimir Bespalov <vlad.bespalov@jetstreamsoft.com>
Date:   Sat Nov 22 19:58:08 2025 -0800

    libstdc++: Fix pretty printer lookup for class templates [PR122812]
    
    Under some circumstances the type.name of a pair<> type starts with
    "struct". This confuses GDB when we use gdb.lookup_type for the name of
    template specialization using "struct pair<...>" in its template
    argument list.
    
    Using type.tag avoids this problem.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/122812
            * python/libstdcxx/v6/printers.py (lookup_templ_spec): Use
            gdb.Type.tag if present.

Diff:
---
 libstdc++-v3/python/libstdcxx/v6/printers.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/python/libstdcxx/v6/printers.py b/libstdc++-v3/python/libstdcxx/v6/printers.py
index f7f0489abf9a..abb072f8a2ba 100644
--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -133,7 +133,11 @@ def lookup_templ_spec(templ, *args):
     """
     Lookup template specialization templ<args...>.
     """
-    t = '{}<{}>'.format(templ, ', '.join([str(a) for a in args]))
+    # Similar to PR67440, str(a) might contain unexpected type qualifiers.
+    t = '{}<{}>'.format(templ, ', '.join([ \
+            a.tag if isinstance(a, gdb.Type) and a.tag \
+            else str(a) \
+        for a in args]))
     try:
         return gdb.lookup_type(t)
     except gdb.error as e: