From 7d074e7f9329fa87fc8ef722df7095220b665751 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Mon, 3 Nov 2025 06:33:01 +0000
Subject: [PATCH v4 2/4] Introduce PG_DEPRECATED() and deprecate
 XLogRecPtrIsInvalid()

This commit creates a new macro PG_DEPRECATED() to mark a declaration as
deprecated with a custom message. The compiler will emit a warning when the
deprecated entity is used.

Then it makes use of this new macro to emit a deprecated message about
XLogRecPtrIsInvalid() as of version 24 (means until the new macro is available
on all the supported major versions).
---
 src/include/access/xlogdefs.h | 14 +++++++++++---
 src/include/c.h               | 15 +++++++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)
  46.3% src/include/access/
  53.6% src/include/

diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index b16b2a1c8a3..2589a21083b 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -32,10 +32,18 @@ typedef uint64 XLogRecPtr;
  * New code should use XLogRecPtrIsValid() instead of XLogRecPtrIsInvalid()
  * for consistency with the affirmative form of other *IsValid() macros and to
  * avoid awkward double negative.
- * This macro is retained for convenience of third-party code but could
- * be deprecated in the future.
+ * This function is retained for convenience of third-party code but is/will be
+ * deprecated as of version 24.
  */
-#define XLogRecPtrIsInvalid(r)	((r) == InvalidXLogRecPtr)
+#if PG_VERSION_NUM >= 240000
+PG_DEPRECATED("use XLogRecPtrIsValid() instead")
+#endif
+static inline bool
+XLogRecPtrIsInvalid(XLogRecPtr ptr)
+{
+	return ptr == InvalidXLogRecPtr;
+}
+
 /*
  * First LSN to use for "fake" LSNs.
  *
diff --git a/src/include/c.h b/src/include/c.h
index 757dfff4782..60e13cd5d6d 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -227,6 +227,21 @@
 #define PG_USED_FOR_ASSERTS_ONLY pg_attribute_unused()
 #endif
 
+/*
+ * Mark a declaration as deprecated with a custom message. The compiler will
+ * emit a warning when the deprecated entity is used.
+ */
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L || \
+defined(__cplusplus) && __cplusplus >= 201402L
+#define PG_DEPRECATED(msg) [[deprecated(msg)]]
+#elif defined(__GNUC__) || defined(__clang__)
+#define PG_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#elif defined(_MSC_VER)
+#define PG_DEPRECATED(msg) __declspec(deprecated(msg))
+#else
+#define PG_DEPRECATED(msg)
+#endif
+
 /* GCC supports format attributes */
 #if defined(__GNUC__)
 #define pg_attribute_format_arg(a) __attribute__((format_arg(a)))
-- 
2.34.1