[gcc r16-8583] libstdc++: Define __cpp_lib_replaceable_contract_violation_handler.

[Tomasz Kaminski]

https://gcc.gnu.org/g:8beabc8851568da82781ed2a47ef0a08f585fddd

commit r16-8583-g8beabc8851568da82781ed2a47ef0a08f585fddd
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Wed Apr 8 15:46:28 2026 +0200

    libstdc++: Define __cpp_lib_replaceable_contract_violation_handler.
    
    This implements P3886R0: Wording for AT1-057, by defining the
    __cpp_lib_replaceable_contract_violation_handler. The macro is defined
    only if contracts are supported (i.e. under same conditions as
    __cpp_lib_contracts).
    
    GCC supports providing custom violation handler by providing an separate
    defintion of handle_contract_violation. This is supported on the targets
    that uses ELF format, so the macro is defined for with non-zero value
    for them.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/version.def (replaceable_contract_violation_handler)
            [(__cplusplus > 202302L) && (__cpp_contracts >= 202502L)]:
            Define to 202603 for ELF targets, and 0 otherwise.
            * include/bits/version.h: Regenerate.
            * include/std/contracts: Define
            __cpp_lib_replaceable_contract_violation_handler.
    
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/version.def | 15 +++++++++++++++
 libstdc++-v3/include/bits/version.h   | 15 +++++++++++++++
 libstdc++-v3/include/std/contracts    |  1 +
 3 files changed, 31 insertions(+)

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 3b4a0d4fdc05..b88d9c3483f8 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -2349,6 +2349,21 @@ ftms = {
   };
 };
 
+ftms = {
+  name = replaceable_contract_violation_handler;
+  values = {
+    v = 202603;
+    cxxmin = 26;
+    extra_cond = "__cpp_contracts >= 202502L "
+    "&& __ELF__";
+  };
+  values = {
+    v = 0;
+    cxxmin = 26;
+    extra_cond = "__cpp_contracts >= 202502L";
+  };
+};
+
 ftms = {
   name = simd;
   values = {
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 59719b4f8116..24ec0175e1e4 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2616,6 +2616,21 @@
 #endif /* !defined(__cpp_lib_contracts) */
 #undef __glibcxx_want_contracts
 
+#if !defined(__cpp_lib_replaceable_contract_violation_handler)
+# if (__cplusplus >  202302L) && (__cpp_contracts >= 202502L && __ELF__)
+#  define __glibcxx_replaceable_contract_violation_handler 202603L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_replaceable_contract_violation_handler)
+#   define __cpp_lib_replaceable_contract_violation_handler 202603L
+#  endif
+# elif (__cplusplus >  202302L) && (__cpp_contracts >= 202502L)
+#  define __glibcxx_replaceable_contract_violation_handler 0L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_replaceable_contract_violation_handler)
+#   define __cpp_lib_replaceable_contract_violation_handler 0L
+#  endif
+# endif
+#endif /* !defined(__cpp_lib_replaceable_contract_violation_handler) */
+#undef __glibcxx_want_replaceable_contract_violation_handler
+
 #if !defined(__cpp_lib_simd)
 # if (__cplusplus >  202302L) && _GLIBCXX_HOSTED && (__cpp_structured_bindings >= 202411L && __cpp_expansion_statements >= 202411L && __SSE2__)
 #  define __glibcxx_simd 202506L
diff --git a/libstdc++-v3/include/std/contracts b/libstdc++-v3/include/std/contracts
index c1fe54750af9..a0575fbefd93 100644
--- a/libstdc++-v3/include/std/contracts
+++ b/libstdc++-v3/include/std/contracts
@@ -33,6 +33,7 @@
 #pragma GCC system_header
 
 #define __glibcxx_want_contracts
+#define __glibcxx_want_replaceable_contract_violation_handler
 #include <bits/version.h>
 
 #ifdef __cpp_lib_contracts