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

src/db/plugins/simple/Directory.hxx

@@ -44,7 +44,6 @@ static constexpr unsigned DEVICE_INARCHIVE = -1;
 static constexpr unsigned DEVICE_CONTAINER = -2;
 
 class SongFilter;
-class Error;
 class Database;
 
 struct Directory {
@@ -266,10 +265,9 @@ public:
 	/**
 	 * Caller must lock #db_mutex.
 	 */
-	bool Walk(bool recursive, const SongFilter *match,
+	void Walk(bool recursive, const SongFilter *match,
 		  VisitDirectory visit_directory, VisitSong visit_song,
-		  VisitPlaylist visit_playlist,
-		  Error &error) const;
+		  VisitPlaylist visit_playlist) const;
 
 	gcc_pure
 	LightDirectory Export() const;

src/db/plugins/simple/Mount.cxx

@@ -63,12 +63,11 @@ PrefixVisitPlaylist(const char *base, const VisitPlaylist &visit_playlist,
 		       PrefixedLightDirectory(directory, base));
 }
 
-bool
+void
 WalkMount(const char *base, const Database &db,
 	  bool recursive, const SongFilter *filter,
 	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
-	  const VisitPlaylist &visit_playlist,
-	  Error &error)
+	  const VisitPlaylist &visit_playlist)
 {
 	using namespace std::placeholders;
 
@@ -87,6 +86,5 @@ WalkMount(const char *base, const Database &db,
 		vp = std::bind(PrefixVisitPlaylist,
 			       base, std::ref(visit_playlist), _1, _2);
 
-	return db.Visit(DatabaseSelection("", recursive, filter),
-			vd, vs, vp, error);
+	db.Visit(DatabaseSelection("", recursive, filter), vd, vs, vp);
 }

src/db/plugins/simple/Mount.hxx

@@ -24,13 +24,11 @@
 
 class Database;
 class SongFilter;
-class Error;
 
-bool
+void
 WalkMount(const char *base, const Database &db,
 	  bool recursive, const SongFilter *filter,
 	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
-	  const VisitPlaylist &visit_playlist,
-	  Error &error);
+	  const VisitPlaylist &visit_playlist);
 
 #endif

src/db/plugins/simple/SimpleDatabasePlugin.cxx

@@ -23,6 +23,7 @@
 #include "db/DatabasePlugin.hxx"
 #include "db/Selection.hxx"
 #include "db/Helpers.hxx"
+#include "db/Stats.hxx"
 #include "db/UniqueTags.hxx"
 #include "db/LightDirectory.hxx"
 #include "Directory.hxx"
@@ -37,7 +38,6 @@
 #include "config/Block.hxx"
 #include "fs/FileSystem.hxx"
 #include "util/CharUtil.hxx"
-#include "util/Error.hxx"
 #include "util/Domain.hxx"
 #include "Log.hxx"
 
@@ -261,12 +261,11 @@ SimpleDatabase::ReturnSong(gcc_unused const LightSong *song) const
 #endif
 }
 
-bool
+void
 SimpleDatabase::Visit(const DatabaseSelection &selection,
 		      VisitDirectory visit_directory,
 		      VisitSong visit_song,
-		      VisitPlaylist visit_playlist,
-		      Error &error) const
+		      VisitPlaylist visit_playlist) const
 {
 	ScopeDatabaseLock protect;
 
@@ -277,10 +276,10 @@ SimpleDatabase::Visit(const DatabaseSelection &selection,
 		if (selection.recursive && visit_directory)
 			visit_directory(r.directory->Export());
 
-		return r.directory->Walk(selection.recursive, selection.filter,
-					 visit_directory, visit_song,
-					 visit_playlist,
-					 error);
+		r.directory->Walk(selection.recursive, selection.filter,
+				  visit_directory, visit_song,
+				  visit_playlist);
+		return;
 	}
 
 	if (strchr(r.uri, '/') == nullptr) {
@@ -298,22 +297,18 @@ SimpleDatabase::Visit(const DatabaseSelection &selection,
 			    "No such directory");
 }
 
-bool
+void
 SimpleDatabase::VisitUniqueTags(const DatabaseSelection &selection,
 				TagType tag_type, tag_mask_t group_mask,
-				VisitTag visit_tag,
-				Error &error) const
+				VisitTag visit_tag) const
 {
-	return ::VisitUniqueTags(*this, selection, tag_type, group_mask,
-				 visit_tag,
-				 error);
+	::VisitUniqueTags(*this, selection, tag_type, group_mask, visit_tag);
 }
 
-bool
-SimpleDatabase::GetStats(const DatabaseSelection &selection,
-			 DatabaseStats &stats, Error &error) const
+DatabaseStats
+SimpleDatabase::GetStats(const DatabaseSelection &selection) const
 {
-	return ::GetStats(*this, selection, stats, error);
+	return ::GetStats(*this, selection);
 }
 
 void

src/db/plugins/simple/SimpleDatabasePlugin.hxx

@@ -112,20 +112,16 @@ public:
 	const LightSong *GetSong(const char *uri_utf8) const override;
 	void ReturnSong(const LightSong *song) const override;
 
-	virtual bool Visit(const DatabaseSelection &selection,
-			   VisitDirectory visit_directory,
-			   VisitSong visit_song,
-			   VisitPlaylist visit_playlist,
-			   Error &error) const override;
+	void Visit(const DatabaseSelection &selection,
+		   VisitDirectory visit_directory,
+		   VisitSong visit_song,
+		   VisitPlaylist visit_playlist) const override;
 
-	virtual bool VisitUniqueTags(const DatabaseSelection &selection,
-				     TagType tag_type, tag_mask_t group_mask,
-				     VisitTag visit_tag,
-				     Error &error) const override;
+	void VisitUniqueTags(const DatabaseSelection &selection,
+			     TagType tag_type, tag_mask_t group_mask,
+			     VisitTag visit_tag) const override;
 
-	virtual bool GetStats(const DatabaseSelection &selection,
-			      DatabaseStats &stats,
-			      Error &error) const override;
+	DatabaseStats GetStats(const DatabaseSelection &selection) const override;
 
 	virtual time_t GetUpdateStamp() const override {
 		return mtime;