db/LightSong: make Tag a reference

This enforces the "not nullptr" rule.

src/DetachedSong.cxx

@@ -26,18 +26,17 @@
 DetachedSong::DetachedSong(const LightSong &other)
 	:uri(other.GetURI()),
 	 real_uri(other.real_uri != nullptr ? other.real_uri : ""),
-	 tag(*other.tag),
+	 tag(other.tag),
 	 mtime(other.mtime),
 	 start_time(other.start_time),
 	 end_time(other.end_time) {}
 
 DetachedSong::operator LightSong() const noexcept
 {
-	LightSong result;
+	LightSong result(tag);
 	result.directory = nullptr;
 	result.uri = uri.c_str();
 	result.real_uri = real_uri.empty() ? nullptr : real_uri.c_str();
-	result.tag = &tag;
 	result.mtime = mtime;
 	result.start_time = start_time;
 	result.end_time = end_time;

src/SongFilter.cxx

@@ -164,7 +164,7 @@ SongFilter::Item::Match(const LightSong &song) const noexcept
 		return StringMatch(uri.c_str());
 	}
 
-	return Match(*song.tag);
+	return Match(song.tag);
 }
 
 SongFilter::SongFilter(unsigned tag, const char *value, bool fold_case)

src/SongPrint.cxx

@@ -92,7 +92,7 @@ song_print_info(Response &r, const LightSong &song, bool base) noexcept
 	if (!IsNegative(song.mtime))
 		time_print(r, "Last-Modified", song.mtime);
 
-	tag_print(r, *song.tag);
+	tag_print(r, song.tag);
 }
 
 void

src/db/Count.cxx

@@ -97,9 +97,7 @@ static void
 GroupCountVisitor(TagCountMap &map, TagType group,
 		  const LightSong &song) noexcept
 {
-	assert(song.tag != nullptr);
-
-	const Tag &tag = *song.tag;
+	const Tag &tag = song.tag;
 	if (!CollectGroupCounts(map, group, tag) && group == TAG_ALBUM_ARTIST)
 		/* fall back to "Artist" if no "AlbumArtist" was found */
 		CollectGroupCounts(map, TAG_ARTIST, tag);

src/db/DatabasePrint.cxx

@@ -105,7 +105,7 @@ PrintSongBrief(Response &r, bool base, const LightSong &song) noexcept
 {
 	song_print_uri(r, song, base);
 
-	if (song.tag->has_playlist)
+	if (song.tag.has_playlist)
 		/* this song file has an embedded CUE sheet */
 		print_playlist_in_directory(r, base,
 					    song.directory, song.uri);
@@ -116,7 +116,7 @@ PrintSongFull(Response &r, bool base, const LightSong &song) noexcept
 {
 	song_print_info(r, song, base);
 
-	if (song.tag->has_playlist)
+	if (song.tag.has_playlist)
 		/* this song file has an embedded CUE sheet */
 		print_playlist_in_directory(r, base,
 					    song.directory, song.uri);

src/db/Helpers.cxx

@@ -65,7 +65,7 @@ StatsVisitSong(DatabaseStats &stats, StringSet &artists, StringSet &albums,
 {
 	++stats.song_count;
 
-	StatsVisitTag(stats, artists, albums, *song.tag);
+	StatsVisitTag(stats, artists, albums, song.tag);
 }
 
 DatabaseStats

src/db/LightSong.cxx

@@ -25,10 +25,10 @@ LightSong::GetDuration() const noexcept
 {
 	SongTime a = start_time, b = end_time;
 	if (!b.IsPositive()) {
-		if (tag->duration.IsNegative())
-			return tag->duration;
+		if (tag.duration.IsNegative())
+			return tag.duration;
 
-		b = SongTime(tag->duration);
+		b = SongTime(tag.duration);
 	}
 
 	return SignedSongTime(b - a);

src/db/LightSong.hxx

@@ -57,9 +57,9 @@ struct LightSong {
 	const char *real_uri;
 
 	/**
-	 * Must not be nullptr.
+	 * Metadata.
 	 */
-	const Tag *tag;
+	const Tag &tag;
 
 	/**
 	 * The time stamp of the last file modification.  A negative
@@ -78,6 +78,9 @@ struct LightSong {
 	 */
 	SongTime end_time;
 
+	explicit LightSong(const Tag &_tag) noexcept
+		:tag(_tag) {}
+
 	gcc_pure
 	std::string GetURI() const noexcept {
 		if (directory == nullptr)

src/db/UniqueTags.cxx

@@ -31,8 +31,7 @@ static void
 CollectTags(TagSet &set, TagType tag_type, TagMask group_mask,
 	    const LightSong &song)
 {
-	assert(song.tag != nullptr);
-	const Tag &tag = *song.tag;
+	const Tag &tag = song.tag;
 
 	set.InsertUnique(tag, tag_type, group_mask);
 }

src/db/plugins/ProxyDatabasePlugin.cxx

@@ -203,11 +203,11 @@ Copy(TagBuilder &tag, TagType d_tag,
 }
 
 ProxySong::ProxySong(const mpd_song *song)
+	:LightSong(tag2)
 {
 	directory = nullptr;
 	uri = mpd_song_get_uri(song);
 	real_uri = nullptr;
-	tag = &tag2;
 
 	const auto _mtime = mpd_song_get_last_modified(song);
 	mtime = _mtime > 0

src/db/plugins/simple/Song.cxx

@@ -98,12 +98,11 @@ Song::GetURI() const noexcept
 LightSong
 Song::Export() const noexcept
 {
-	LightSong dest;
+	LightSong dest(tag);
 	dest.directory = parent->IsRoot()
 		? nullptr : parent->GetPath();
 	dest.uri = uri;
 	dest.real_uri = nullptr;
-	dest.tag = &tag;
 	dest.mtime = mtime;
 	dest.start_time = start_time;
 	dest.end_time = end_time;

src/db/plugins/upnp/UpnpDatabasePlugin.cxx

@@ -55,13 +55,13 @@ class UpnpSong : public LightSong {
 
 public:
 	UpnpSong(UPnPDirObject &&object, std::string &&_uri)
-		:uri2(std::move(_uri)),
+		:LightSong(tag2),
+		 uri2(std::move(_uri)),
 		 real_uri2(std::move(object.url)),
 		 tag2(std::move(object.tag)) {
 		directory = nullptr;
 		uri = uri2.c_str();
 		real_uri = real_uri2.c_str();
-		tag = &tag2;
 		mtime = std::chrono::system_clock::time_point::min();
 		start_time = end_time = SongTime::zero();
 	}
@@ -321,11 +321,10 @@ visitSong(const UPnPDirObject &meta, const char *path,
 	if (!visit_song)
 		return;
 
-	LightSong song;
+	LightSong song(meta.tag);
 	song.directory = nullptr;
 	song.uri = path;
 	song.real_uri = meta.url.c_str();
-	song.tag = &meta.tag;
 	song.mtime = std::chrono::system_clock::time_point::min();
 	song.start_time = song.end_time = SongTime::zero();
 

src/queue/PlaylistUpdate.cxx

@@ -50,7 +50,7 @@ UpdatePlaylistSong(const Database &db, DetachedSong &song)
 	}
 
 	song.SetLastModified(original->mtime);
-	song.SetTag(*original->tag);
+	song.SetTag(original->tag);
 
 	db.ReturnSong(original);
 	return true;