TagArchive: add TagBuilder overload with ScanGenericTags() fallback

src/SongUpdate.cxx

@@ -31,8 +31,6 @@
 #include "decoder/DecoderList.hxx"
 #include "tag/Tag.hxx"
 #include "tag/TagBuilder.hxx"
-#include "tag/TagHandler.hxx"
-#include "tag/Generic.hxx"
 #include "TagFile.hxx"
 #include "TagStream.hxx"
 
@@ -127,7 +125,7 @@ Song::UpdateFileInArchive(const Storage &storage)
 		return false;
 
 	TagBuilder tag_builder;
-	if (!tag_archive_scan(path_fs, full_tag_handler, &tag_builder))
+	if (!tag_archive_scan(path_fs, tag_builder))
 		return false;
 
 	tag_builder.Commit(tag);

src/TagArchive.cxx

@@ -20,6 +20,9 @@
 #include "config.h"
 #include "TagArchive.hxx"
 #include "TagStream.hxx"
+#include "tag/Generic.hxx"
+#include "tag/TagHandler.hxx"
+#include "tag/TagBuilder.hxx"
 #include "fs/Path.hxx"
 #include "util/Error.hxx"
 #include "input/InputStream.hxx"
@@ -42,3 +45,15 @@ tag_archive_scan(Path path, const TagHandler &handler, void *handler_ctx)
 
 	return tag_stream_scan(*is, handler, handler_ctx);
 }
+
+bool
+tag_archive_scan(Path path, TagBuilder &builder)
+{
+	assert(!path.IsNull());
+
+	Mutex mutex;
+	Cond cond;
+	InputStreamPtr is(OpenArchiveInputStream(path, mutex, cond,
+						 IgnoreError()));
+	return is && tag_stream_scan(*is, builder);
+}

src/TagArchive.hxx

@@ -24,6 +24,7 @@
 
 class Path;
 struct TagHandler;
+class TagBuilder;
 
 /**
  * Scan the tags of a song file inside an archive.  Invokes matching
@@ -36,4 +37,15 @@ struct TagHandler;
 bool
 tag_archive_scan(Path path, const TagHandler &handler, void *handler_ctx);
 
+/**
+ * Scan the tags of a song file inside an archive.  Invokes matching
+ * decoder plugins, and falls back to generic scanners (APE and ID3)
+ * if no tags were found (but the file was recognized).
+ *
+ * @return true if the file was recognized (even if no metadata was
+ * found)
+ */
+bool
+tag_archive_scan(Path path, TagBuilder &builder);
+
 #endif