logging: rework a bit, maybe support syslog

Seems journal logging fails on NetBSD (no surprise), but has some
unwanted/not-fully-understood side-effects.

In any case, outside Linux there's no use in even trying to use
journald; so we don't do that anymore.

Add conditional support for syslog (requires glib 2.80).

lib/utils/mu-logger.cc

@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2020-2022 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+** Copyright (C) 2020-2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -17,6 +17,9 @@
 **
 */
 
+#include "config.h"
+#include "mu-logger.hh"
+
 #define G_LOG_USE_STRUCTURED
 #include <glib.h>
 #include <glib/gstdio.h>
@@ -31,8 +34,6 @@
 #include <thread>
 #include <mutex>
 
-#include "mu-logger.hh"
-
 using namespace Mu;
 
 static bool			MuLogInitialized = false;
@@ -118,10 +119,29 @@ log_stdouterr(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpo
 	return g_log_writer_standard_streams(level, fields, n_fields, user_data);
 }
 
+
+
+// log to some logging system; the one that is available & works of journal,
+// syslog, file.
 static GLogWriterOutput
-log_journal(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data)
+log_system(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data)
 {
-	return g_log_writer_journald(level, fields, n_fields, user_data);
+	GLogWriterOutput res = G_LOG_WRITER_UNHANDLED;
+
+#ifdef MAYBE_USE_JOURNAL
+	res = g_log_writer_journald(level, fields, n_fields, user_data);
+	if (res == G_LOG_WRITER_HANDLED)
+		return res;
+#endif /*MAYBE_USE_JOURNAL*/
+
+#ifdef MAYBE_USE_SYSLOG
+	/* since glib 2.80 */
+	res = g_log_writer_syslog(level, fields, n_fields, user_data);
+	if (res == G_LOG_WRITER_HANDLED)
+		return res;
+#endif /*MAYBE_USE_SYSLOG*/
+
+	return res = log_file(level, fields, n_fields, user_data);
 }
 
 
@@ -156,11 +176,10 @@ Mu::Logger::Logger(const std::string& path, Mu::Logger::Options opts)
 		    }
 
 		    // log to the journal, or, if not available to a file.
-		    if (any_of(MuLogOptions & Options::File) ||
-			log_journal(level, fields, n_fields, user_data) != G_LOG_WRITER_HANDLED)
-			    return log_file(level, fields, n_fields, user_data);
-		    else
-			    return G_LOG_WRITER_HANDLED;
+		    if (any_of(MuLogOptions & Options::File))
+			return log_file(level, fields, n_fields, user_data);
+
+		    return log_system(level, fields, n_fields, user_data);
 	    },
 	    NULL,
 	    NULL);

lib/utils/tests/meson.build

@@ -50,7 +50,7 @@ test('test-logger',
      executable('test-logger', '../mu-logger.cc',
                 install: false,
                 cpp_args: ['-DBUILD_TESTS'],
-                dependencies: [glib_dep, lib_mu_utils_dep, thread_dep ]))
+                dependencies: [glib_dep, lib_mu_utils_dep,config_h_dep,thread_dep ]))
 
 test('test-option',
      executable('test-option', '../mu-option.cc',

meson.build

@@ -203,6 +203,23 @@ if xapver.version_compare('>= 1.4.23')
   config_h_data.set('HAVE_XAPIAN_FLAG_NGRAMS', 1)
 endif
 
+host_system = host_machine.system()
+#
+# soft dependencies
+#
+
+
+# logging
+
+# if we're on a linux machine, perhaps there's systemd/journald.
+# otherwise, we don't bother.
+if host_machine.system() == 'linux'
+  config_h_data.set('MAYBE_USE_JOURNAL', 1)
+endif
+if cc.has_function('g_log_writer_syslog',dependencies: glib_dep)
+  config_h_data.set('MAYBE_USE_SYSLOG', 1)
+endif
+
 # optionally, use Compact Language Detector2 if we can find it.
 cld2_dep = meson.get_compiler('cpp').find_library('cld2', required: get_option('cld2'))
 if not get_option('cld2').disabled() and cld2_dep.found()
@@ -211,7 +228,7 @@ else
   message('CLD2 not found or disabled; no support for language detection')
 endif
 
-# soft dependencies
+# guile
 guile_dep = dependency('guile-3.0', required: get_option('guile'))
 # allow for a custom guile-extension-dir
 if guile_dep.found()