Cull: add [[nodiscard]]

src/Cull.cxx

@@ -29,10 +29,13 @@ class Cull::DirectoryRef {
 	Directory &directory;
 
 public:
+	[[nodiscard]]
 	explicit DirectoryRef(Directory &_directory) noexcept
 		:directory(_directory.Ref()) {}
 
 	struct Adopt {};
+
+	[[nodiscard]]
 	DirectoryRef(Adopt, Directory &_directory) noexcept
 		:directory(_directory) {}
 
@@ -43,10 +46,12 @@ class Cull::DirectoryRef {
 	DirectoryRef(const DirectoryRef &) = delete;
 	DirectoryRef &operator=(const DirectoryRef &) = delete;
 
+	[[nodiscard]]
 	Directory &operator*() const noexcept{
 		return directory;
 	}
 
+	[[nodiscard]]
 	Directory *operator->() const noexcept{
 		return &directory;
 	}
@@ -61,6 +66,7 @@ struct Cull::File final : IntrusiveTreeSetHook<> {
 
 	const std::string name;
 
+	[[nodiscard]]
 	File(Directory &_parent, std::string &&_name,
 	     FileTime _time, const uint_least64_t _size) noexcept
 		:parent(_parent), time(_time), size(_size),
@@ -97,6 +103,7 @@ class Cull::StatItem : public IntrusiveListHook<> {
 	Co::InvokeTask invoke_task;
 
 public:
+	[[nodiscard]]
 	StatItem(Cull &_cull, Directory &_directory, const char *_name) noexcept
 		:cull(_cull), directory(_directory), name(_name) {}
 
@@ -106,6 +113,7 @@ class Cull::StatItem : public IntrusiveListHook<> {
 	}
 
 private:
+	[[nodiscard]]
 	Co::InvokeTask Run(Uring::Queue &uring);
 
 	void OnCompletion(std::exception_ptr error) noexcept {

src/Cull.hxx

@@ -140,6 +140,7 @@ class Cull {
 	const FileTime discard_older_than;
 
 public:
+	[[nodiscard]]
 	Cull(EventLoop &_event_loop, Uring::Queue &_uring,
 	     FileDescriptor _dev_cachefiles, FileDescriptor root_fd,
 	     std::size_t _cull_files, uint_least64_t _cull_bytes,