[PATCH] libstdc++: Defined __cpp_lib_replaceable_contract_violation_handler.

[Tomasz Kamiński]

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.
---
>From the discussion with Jason, this for sure is supported for ELF
targets. We were not sure regarding Darwin, but we could always expand
the set of targets where macro is defined.

OK for trunk?

 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 cfb90533ce4..65a1d6d2660 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -2351,6 +2351,21 @@ 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 22dd31b9d32..4059a8a767b 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2626,6 +2626,21 @@
 #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 c1fe54750af..a0575fbefd9 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
-- 
2.53.0