https://github.com/ceph/ceph/pull/66928

From 4965dbac4bd17973eb15fe09d2a046a509b4a65a Mon Sep 17 00:00:00 2001
From: "Z. Liu" <zhixu.liu@gmail.com>
Date: Wed, 14 Jan 2026 22:46:39 +0800
Subject: [PATCH] rgw: remove FMT_STRING to fix clang 20+ build failure

Fix a build failure with Clang 20+ using -std=c++20, where fmt
(v9.1.0, v11.0.0, and possibly other versions) fails to parse
format strings at compile-time in a consteval context. This is
a known issue in fmt, fixed in fmt v11.1.0 (see
https://github.com/fmtlib/fmt/commit/6797f0c39a4ef13061cbc3bb850c35af7428fdc4).

The following error occurs when building rgw_auth_s3.cc:

  src/rgw/rgw_auth_s3.cc:600:22: error: call to consteval function
  'fmt::basic_format_string<...>' is not a constant expression

Removing FMT_STRING avoids compile-time format string parsing
and restores buildability across different toolchains.

Test case:

  #include <fmt/format.h>

  std::string gen_v4_scope(const std::string& region)
  {
    return fmt::format(FMT_STRING("{:s}"), region);
  }

Compile with:

  clang -isystem fmt/include -std=c++20 -c test.cc

Signed-off-by: Z. Liu <zhixu.liu@gmail.com>

diff --git a/src/rgw/rgw_auth_s3.cc b/src/rgw/rgw_auth_s3.cc
index c14a937685a..b31b0279d8e 100644
--- a/src/rgw/rgw_auth_s3.cc
+++ b/src/rgw/rgw_auth_s3.cc
@@ -605,7 +605,7 @@ string gen_v4_scope(const ceph::real_time& timestamp,
   auto mon = bt.tm_mon + 1;
   auto day = bt.tm_mday;
 
-  return fmt::format(FMT_STRING("{:d}{:02d}{:02d}/{:s}/{:s}/aws4_request"),
+  return fmt::format("{:d}{:02d}{:02d}/{:s}/{:s}/aws4_request",
                      year, mon, day, region, service);
 }
 
-- 
2.49.1