db/simple/ExportedSong: new class

src/db/plugins/simple/Directory.cxx

@@ -18,11 +18,11 @@
  */
 
 #include "Directory.hxx"
+#include "ExportedSong.hxx"
 #include "SongSort.hxx"
 #include "Song.hxx"
 #include "Mount.hxx"
 #include "db/LightDirectory.hxx"
-#include "song/LightSong.hxx"
 #include "db/Uri.hxx"
 #include "db/DatabaseLock.hxx"
 #include "db/Interface.hxx"
@@ -234,7 +234,7 @@ Directory::Walk(bool recursive, const SongFilter *filter,
 
 	if (visit_song) {
 		for (auto &song : songs){
-			const LightSong song2 = song.Export();
+			const auto song2 = song.Export();
 			if (filter == nullptr || filter->Match(song2))
 				visit_song(song2);
 		}

src/db/plugins/simple/ExportedSong.hxx

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2003-2021 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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 2 of the License, 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.
+ */
+
+#ifndef MPD_DB_SIMPLE_EXPORTED_SONG_HXX
+#define MPD_DB_SIMPLE_EXPORTED_SONG_HXX
+
+#include "song/LightSong.hxx"
+
+/**
+ * The return type for Song::Export().  In addition to implementing
+ * #LightSong, it hold allocations necessary to represent the #Song as
+ * a #LightSong, e.g. a merged #Tag.
+ */
+class ExportedSong : public LightSong {
+public:
+	using LightSong::LightSong;
+};
+
+#endif

src/db/plugins/simple/SimpleDatabasePlugin.cxx

@@ -238,20 +238,20 @@ SimpleDatabase::GetSong(std::string_view uri) const
 		throw DatabaseError(DatabaseErrorCode::NOT_FOUND,
 				    "No such song");
 
-	light_song.Construct(song->Export());
+	exported_song.Construct(song->Export());
 
 #ifndef NDEBUG
 	++borrowed_song_count;
 #endif
 
-	return &light_song.Get();
+	return &exported_song.Get();
 }
 
 void
 SimpleDatabase::ReturnSong([[maybe_unused]] const LightSong *song) const noexcept
 {
 	assert(song != nullptr);
-	assert(song == prefixed_light_song || song == &light_song.Get());
+	assert(song == prefixed_light_song || song == &exported_song.Get());
 
 	if (prefixed_light_song != nullptr) {
 		delete prefixed_light_song;
@@ -262,7 +262,7 @@ SimpleDatabase::ReturnSong([[maybe_unused]] const LightSong *song) const noexcep
 		--borrowed_song_count;
 #endif
 
-		light_song.Destruct();
+		exported_song.Destruct();
 	}
 }
 
@@ -316,7 +316,7 @@ SimpleDatabase::Visit(const DatabaseSelection &selection,
 		if (visit_song) {
 			Song *song = r.directory->FindSong(r.rest);
 			if (song != nullptr) {
-				const LightSong song2 = song->Export();
+				const auto song2 = song->Export();
 				if (selection.Match(song2))
 					visit_song(song2);
 

src/db/plugins/simple/SimpleDatabasePlugin.hxx

@@ -20,10 +20,10 @@
 #ifndef MPD_SIMPLE_DATABASE_PLUGIN_HXX
 #define MPD_SIMPLE_DATABASE_PLUGIN_HXX
 
+#include "ExportedSong.hxx"
 #include "db/Interface.hxx"
 #include "db/Ptr.hxx"
 #include "fs/AllocatedPath.hxx"
-#include "song/LightSong.hxx"
 #include "util/Manual.hxx"
 #include "util/Compiler.h"
 #include "config.h"
@@ -63,7 +63,7 @@ class SimpleDatabase : public Database {
 	/**
 	 * A buffer for GetSong().
 	 */
-	mutable Manual<LightSong> light_song;
+	mutable Manual<ExportedSong> exported_song;
 
 #ifndef NDEBUG
 	mutable unsigned borrowed_song_count;

src/db/plugins/simple/Song.cxx

@@ -18,6 +18,7 @@
  */
 
 #include "Song.hxx"
+#include "ExportedSong.hxx"
 #include "Directory.hxx"
 #include "tag/Tag.hxx"
 #include "song/DetachedSong.hxx"
@@ -53,10 +54,10 @@ Song::GetURI() const noexcept
 	}
 }
 
-LightSong
+ExportedSong
 Song::Export() const noexcept
 {
-	LightSong dest(filename.c_str(), tag);
+	ExportedSong dest(filename.c_str(), tag);
 	if (!parent.IsRoot())
 		dest.directory = parent.GetPath();
 	if (!target.empty())

src/db/plugins/simple/Song.hxx

@@ -32,8 +32,8 @@
 #include <string>
 
 struct StringView;
-struct LightSong;
 struct Directory;
+class ExportedSong;
 class DetachedSong;
 class Storage;
 class ArchiveFile;
@@ -153,7 +153,7 @@ struct Song {
 	std::string GetURI() const noexcept;
 
 	gcc_pure
-	LightSong Export() const noexcept;
+	ExportedSong Export() const noexcept;
 };
 
 typedef boost::intrusive::list<Song,