config: allow configuring partitions

This just allows creating empty partitions.  More features to come.

NEWS

@@ -15,6 +15,7 @@ ver 0.24 (not yet released)
   - new tag "Mood"
 * switch to C++20
   - GCC 10 or clang 11 (or newer) recommended
+* static partition configuration
 * remove Haiku support
 
 ver 0.23.9 (not yet released)

doc/user.rst

@@ -297,6 +297,38 @@ configure this plugin, add a :code:`database` block to
 More information can be found in the :ref:`database_plugins`
 reference.
 
+
+Configuring Partitions
+----------------------
+
+:program:`MPD` can have multiple "partitions", that is, multiple
+independent players, each with their own queue and outputs.  All
+partitions share one database.  By default, there is only one
+partition called "default".  Additional partitions can be created in
+the configuration file with ``partition`` blocks or at runtime with
+the :ref:`newpartition <command_newpartition>` command.
+
+Example for specifying an additional partition in the configuration
+file:
+
+.. code-block:: none
+
+    partition {
+        name "foo"
+    }
+
+The following options are available in ``partition`` blocks:
+
+.. list-table::
+   :widths: 20 80
+   :header-rows: 1
+
+   * - Name
+     - Description
+   * - **name**
+     - The name of the partition.
+
+
 Configuring neighbor plugins
 ----------------------------
 

src/Main.cxx

@@ -410,6 +410,15 @@ MainConfigured(const CommandLineOptions &options,
 		partition.UpdateEffectiveReplayGainMode();
 	}
 
+	raw_config.WithEach(ConfigBlockOption::PARTITION, [&](const auto &block){
+		const char *name = block.GetBlockValue("name");
+		if (name == nullptr)
+			throw std::runtime_error("Missing 'name'");
+
+		instance.partitions.emplace_back(instance, name,
+						 partition_config);
+	});
+
 	client_manager_init(raw_config);
 	const ScopeInputPluginsInit input_plugins_init(raw_config,
 						       instance.io_thread.GetEventLoop());

src/config/Option.hxx

@@ -97,6 +97,7 @@ enum class ConfigBlockOption {
 	AUDIO_FILTER,
 	DATABASE,
 	NEIGHBORS,
+	PARTITION,
 	MAX
 };
 

src/config/Templates.cxx

@@ -96,6 +96,7 @@ const ConfigTemplate config_block_templates[] = {
 	{ "filter", true },
 	{ "database" },
 	{ "neighbors", true },
+	{ "partition", true },
 };
 
 static constexpr unsigned n_config_block_templates =