config/Param: split block-specific attributes to new struct ConfigBlock

The old struct config_param remains only for top-level string options.

src/config/Block.hxx

@@ -21,9 +21,14 @@
 #define MPD_CONFIG_BLOCK_HXX
 
 #include "check.h"
+#include "Param.hxx"
 #include "Compiler.h"
 
 #include <string>
+#include <vector>
+
+class Error;
+class AllocatedPath;
 
 struct BlockParam {
 	std::string name;
@@ -50,4 +55,71 @@ struct BlockParam {
 	bool GetBoolValue() const;
 };
 
+struct ConfigBlock {
+	/**
+	 * The next #ConfigBlock with the same name.  The destructor
+	 * deletes the whole chain.
+	 */
+	ConfigBlock *next;
+
+	int line;
+
+	std::vector<BlockParam> block_params;
+
+	/**
+	 * This flag is false when nobody has queried the value of
+	 * this option yet.
+	 */
+	bool used;
+
+	explicit ConfigBlock(int _line=-1)
+		:next(nullptr), line(_line), used(false) {}
+
+	ConfigBlock(const ConfigBlock &) = delete;
+
+	~ConfigBlock();
+
+	ConfigBlock &operator=(const ConfigBlock &) = delete;
+
+	/**
+	 * Determine if this is a "null" instance, i.e. an empty
+	 * object that was synthesized and not loaded from a
+	 * configuration file.
+	 */
+	bool IsNull() const {
+		return line < 0;
+	}
+
+	gcc_nonnull_all
+	void AddBlockParam(const char *_name, const char *_value,
+			   int _line=-1) {
+		block_params.emplace_back(_name, _value, _line);
+	}
+
+	gcc_nonnull_all gcc_pure
+	const BlockParam *GetBlockParam(const char *_name) const;
+
+	gcc_pure
+	const char *GetBlockValue(const char *name,
+				  const char *default_value=nullptr) const;
+
+	/**
+	 * Same as config_get_path(), but looks up the setting in the
+	 * specified block.
+	 */
+	AllocatedPath GetBlockPath(const char *name, const char *default_value,
+				   Error &error) const;
+
+	AllocatedPath GetBlockPath(const char *name, Error &error) const;
+
+	gcc_pure
+	int GetBlockValue(const char *name, int default_value) const;
+
+	gcc_pure
+	unsigned GetBlockValue(const char *name, unsigned default_value) const;
+
+	gcc_pure
+	bool GetBlockValue(const char *name, bool default_value) const;
+};
+
 #endif