Remove the use of config.h

Prior to this change, pinelog relied on an autoconf generated config.h
which checked if the compiler supports __attribute__ with constructor,
destructor and format. However, most modern compilers already have
support for this, and we can use the __has_attribute special operator
instead to check for this at compile time.

By eliminating the need to create a config.h file, it simplifies
integration into other projects that may not have one.

README.md

@@ -125,11 +125,3 @@ definitions.
 Pinelog is intended to be integrated into your application source tree, either
 by means of including the sources directly, or by including the repository as
 a Git submodule or subtree.
-
-The default build of Pinelog uses an autotools generated `config.h` file, which
-includes checks for the following GCC attributes. If you don't care about these,
-then either create a dummy config.h which includes the macros
-`HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR`, `HAVE_FUNC_ATTRIBUTE_DESTRUCTOR` and
-`HAVE_FUNC_ATTRIBUTE_FORMAT`, or use the `AX_GCC_FUNC_ATTRIBUTE` macro to check
-for the `constructor`, `destructor` and `format` attributes in your
-application's `configure.ac` file.

configure.ac

@@ -16,14 +16,8 @@ LT_INIT
 PKG_PROG_PKG_CONFIG
 PKG_INSTALLDIR
 AX_COMPILER_FLAGS
-AX_GCC_FUNC_ATTRIBUTE([constructor])
-AX_GCC_FUNC_ATTRIBUTE([destructor])
-AX_GCC_FUNC_ATTRIBUTE([format])
 
 AC_SUBST([PINELOG_CFLAGS])
 
-# Configuration headers
-AC_CONFIG_HEADERS([config.h])
-
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT

pinelog.c

@@ -6,7 +6,6 @@
  * SPDX-License-Identifier: MIT
  */
 
-#include "config.h"
 #include <stdio.h>
 #include <stdarg.h>
 #include <time.h>
@@ -78,8 +77,10 @@ static FILE *output_stream = NULL;
 static int log_level = PINELOG_DEFAULT_LEVEL;
 
 /* Initialize defaults */
-#if HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
-__attribute__((constructor))
+#if defined __has_attribute
+#   if __has_attribute(constructor)
+        __attribute__((constructor))
+#   endif
 #endif
 void pinelog_set_defaults(void)
 {
@@ -87,8 +88,10 @@ void pinelog_set_defaults(void)
     log_level = PINELOG_DEFAULT_LEVEL;
 }
 
-#if HAVE_FUNC_ATTRIBUTE_DESTRUCTOR
-__attribute__((destructor))
+#if defined __has_attribute
+#   if __has_attribute(destructor)
+        __attribute__((destructor))
+#   endif
 #endif
 void pinelog_close_output_stream(void)
 {
@@ -167,7 +170,8 @@ void pinelog_log_message(int level, const char *file, int line, const char *fmt,
         level = PINELOG_LVL_TRACE;
     }
 
-    #if !HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
+    #if defined __has_attribute
+    #if !__has_attribute(constructor)
     /*
      * Validate and set output stream. Only necessary if the compiler doesn't
      * support the constructor attribute
@@ -176,6 +180,7 @@ void pinelog_log_message(int level, const char *file, int line, const char *fmt,
         output_stream = PINELOG_DEFAULT_STREAM;
     }
     #endif
+    #endif
 
     #if PINELOG_SHOW_DATE
     do {

pinelog.h

@@ -18,7 +18,6 @@
 #ifndef LOGGING_H
 #define LOGGING_H
 
-#include "config.h"
 #include <stdio.h>
 #ifndef PINELOG_TEST
 #include <stdlib.h>
@@ -123,10 +122,11 @@ int pinelog_get_level(void);
  *
  * @returns None
  */
-#if HAVE_FUNC_ATTRIBUTE_FORMAT
-__attribute__((format(printf, 4, 5)))
+#if defined __has_attribute
+#   if __has_attribute(format)
+        __attribute__((format(printf, 4, 5)))
+#   endif
 #endif
-
 void pinelog_log_message(int level, const char *file, int line, const char *fmt, ...);
 
 // Test harness will redefine pinelog_exit