From 3bb97e7707a0be8c371cb9c704cb1e21062e1fc6 Mon Sep 17 00:00:00 2001
From: Koichi Sasada <ko1@atdot.net>
Date: Wed, 10 Dec 2025 04:32:34 +0900
Subject: [PATCH] `_RUBY_DEBUG_LOG` usable anywhere

even if `USE_RUBY_DEBUG_LOG=0`.
It becomes `fprintf(stderr, ...)`.
---
 debug.c    | 18 ++++++++++++++++++
 vm_debug.h |  8 ++++----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/debug.c b/debug.c
index b92faa8f36..4daee2bd1c 100644
--- a/debug.c
+++ b/debug.c
@@ -708,4 +708,22 @@ ruby_debug_log_dump(const char *fname, unsigned int n)
         fclose(fp);
     }
 }
+
+#else
+
+#undef ruby_debug_log
+void
+ruby_debug_log(const char *file, int line, const char *func_name, const char *fmt, ...)
+{
+    va_list args;
+
+    fprintf(stderr, "[%s:%d] %s: ", file, line, func_name);
+
+    va_start(args, fmt);
+    vfprintf(stderr, fmt, args);
+    va_end(args);
+
+    fprintf(stderr, "\n");
+}
+
 #endif // #if USE_RUBY_DEBUG_LOG
diff --git a/vm_debug.h b/vm_debug.h
index d0bc81574a..cf80232f3a 100644
--- a/vm_debug.h
+++ b/vm_debug.h
@@ -88,6 +88,10 @@ void ruby_debug_log(const char *file, int line, const char *func_name, const cha
 void ruby_debug_log_print(unsigned int n);
 bool ruby_debug_log_filter(const char *func_name, const char *file_name);
 
+// convenient macro to log even if the USE_RUBY_DEBUG_LOG macro is not specified.
+// You can use this macro for temporary usage (you should not commit it).
+#define _RUBY_DEBUG_LOG(...) ruby_debug_log(__FILE__, __LINE__, RUBY_FUNCTION_NAME_STRING, "" __VA_ARGS__)
+
 #if RBIMPL_COMPILER_IS(GCC) && defined(__OPTIMIZE__)
 # define ruby_debug_log(...) \
     RB_GNUC_EXTENSION_BLOCK( \
@@ -97,10 +101,6 @@ bool ruby_debug_log_filter(const char *func_name, const char *file_name);
         RBIMPL_WARNING_POP())
 #endif
 
-// convenient macro to log even if the USE_RUBY_DEBUG_LOG macro is not specified.
-// You can use this macro for temporary usage (you should not commit it).
-#define _RUBY_DEBUG_LOG(...) ruby_debug_log(__FILE__, __LINE__, RUBY_FUNCTION_NAME_STRING, "" __VA_ARGS__)
-
 #if USE_RUBY_DEBUG_LOG
 # define RUBY_DEBUG_LOG_ENABLED(func_name, file_name)                     \
     (ruby_debug_log_mode && ruby_debug_log_filter(func_name, file_name))