db/Interface: migrate visitor methods from class Error to C++ exceptions

src/db/plugins/simple/Directory.cxx

@@ -32,7 +32,6 @@
 #include "fs/Traits.hxx"
 #include "util/Alloc.hxx"
 #include "util/DeleteDisposer.hxx"
-#include "util/Error.hxx"
 
 #include <assert.h>
 #include <string.h>
@@ -218,14 +217,11 @@ Directory::Sort()
 		child.Sort();
 }
 
-bool
+void
 Directory::Walk(bool recursive, const SongFilter *filter,
 		VisitDirectory visit_directory, VisitSong visit_song,
-		VisitPlaylist visit_playlist,
-		Error &error) const
+		VisitPlaylist visit_playlist) const
 {
-	assert(!error.IsDefined());
-
 	if (IsMount()) {
 		assert(IsEmpty());
 
@@ -233,11 +229,11 @@ Directory::Walk(bool recursive, const SongFilter *filter,
 		   because the child's SimpleDatabasePlugin::Visit()
 		   call will lock it again */
 		const ScopeDatabaseUnlock unlock;
-		return WalkMount(GetPath(), *mounted_database,
-				 recursive, filter,
-				 visit_directory, visit_song,
-				 visit_playlist,
-				 error);
+		WalkMount(GetPath(), *mounted_database,
+			  recursive, filter,
+			  visit_directory, visit_song,
+			  visit_playlist);
+		return;
 	}
 
 	if (visit_song) {
@@ -257,14 +253,11 @@ Directory::Walk(bool recursive, const SongFilter *filter,
 		if (visit_directory)
 			visit_directory(child.Export());
 
-		if (recursive &&
-		    !child.Walk(recursive, filter,
-				visit_directory, visit_song, visit_playlist,
-				error))
-			return false;
+		if (recursive)
+			child.Walk(recursive, filter,
+				   visit_directory, visit_song,
+				   visit_playlist);
 	}
-
-	return true;
 }
 
 LightDirectory