lib: create mu-xapian-db, mu-config

XapianDb is a fairly thing wrapper around Xapian, which handles locking,
exception handling and some tracking.

On top of that, Config add a configuration database for type /
introspectable configuration info.

lib/mu-config.cc

@@ -0,0 +1,88 @@
+/*
+** Copyright (C) 2023 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
+** Free Software Foundation; either version 3, or (at your option) any
+** later version.
+**
+** This program is distributed in the hope that it will be useful,
+** but WITHOUT ANY WARRANTY; without even the implied warranty of
+** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+** GNU General Public License for more details.
+**
+** You should have received a copy of the GNU General Public License
+** along with this program; if not, write to the Free Software Foundation,
+** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+**
+*/
+
+#include "mu-config.hh"
+
+using namespace Mu;
+
+constexpr /*static*/ bool
+validate_props()
+{
+	size_t id{0};
+	for (auto&& prop: Config::properties) {
+
+		// ids must match
+		if (static_cast<size_t>(prop.id) != id)
+			return false;
+		++id;
+	}
+
+	return true;
+}
+
+#ifdef BUILD_TESTS
+#define static_assert g_assert_true
+#endif /*BUILD_TESTS*/
+
+[[maybe_unused]]
+static void
+test_props()
+{
+	static_assert(validate_props());
+}
+
+#ifdef BUILD_TESTS
+/*
+ * Tests.
+ *
+ */
+
+#include "utils/mu-test-utils.hh"
+
+static void
+test_basic()
+{
+	MemDb db;
+	Config conf_db{db};
+
+	using Id = Config::Id;
+
+	{
+		const auto rmd = conf_db.get<Id::RootMaildir>();
+		g_assert_true(rmd.empty());
+	}
+
+	{
+		conf_db.set<Id::RootMaildir>("/home/djcb/Maildir");
+		const auto rmd = conf_db.get<Id::RootMaildir>();
+		assert_equal(rmd, "/home/djcb/Maildir");
+	}
+}
+
+int
+main(int argc, char* argv[])
+{
+	mu_test_init(&argc, &argv);
+
+	g_test_add_func("/config-db/props", test_props);
+	g_test_add_func("/config-db/basic", test_basic);
+
+	return g_test_run();
+}
+#endif /*BUILD_TESTS*/