add various nodiscard

src/archive/plugins/Iso9660ArchivePlugin.cxx

@@ -162,7 +162,7 @@ class Iso9660InputStream final : public InputStream {
 		std::array<uint8_t, ISO_BLOCKSIZE> data;
 
 	public:
-		ConstBuffer<uint8_t> Read() const noexcept {
+		[[nodiscard]] ConstBuffer<uint8_t> Read() const noexcept {
 			assert(fill <= data.size());
 			assert(position <= fill);
 

src/event/ServerSocket.cxx

@@ -91,7 +91,7 @@ public:
 	}
 #endif
 
-	bool IsDefined() const noexcept {
+	[[nodiscard]] bool IsDefined() const noexcept {
 		return event.IsDefined();
 	}
 

src/event/SignalMonitor.cxx

@@ -62,7 +62,7 @@ public:
 #endif
 	}
 
-	auto &GetEventLoop() const noexcept {
+	[[nodiscard]] auto &GetEventLoop() const noexcept {
 		return event.GetEventLoop();
 	}
 

src/lib/curl/Global.cxx

@@ -61,7 +61,7 @@ public:
 	CurlSocket(const CurlSocket &) = delete;
 	CurlSocket &operator=(const CurlSocket &) = delete;
 
-	auto &GetEventLoop() const noexcept {
+	[[nodiscard]] auto &GetEventLoop() const noexcept {
 		return socket_event.GetEventLoop();
 	}
 
@@ -73,7 +73,7 @@ public:
 				  void *userp, void *socketp) noexcept;
 
 private:
-	SocketDescriptor GetSocket() const noexcept {
+	[[nodiscard]] SocketDescriptor GetSocket() const noexcept {
 		return socket_event.GetSocket();
 	}
 

src/mixer/plugins/AlsaMixerPlugin.cxx

@@ -128,13 +128,13 @@ private:
 	}
 
 	[[gnu::pure]]
-	double GetNormalizedVolume() const noexcept {
+	[[nodiscard]] double GetNormalizedVolume() const noexcept {
 		return get_normalized_playback_volume(elem,
 						      SND_MIXER_SCHN_FRONT_LEFT);
 	}
 
 	[[gnu::pure]]
-	unsigned GetPercentVolume() const noexcept {
+	[[nodiscard]] unsigned GetPercentVolume() const noexcept {
 		return NormalizedToPercent(GetNormalizedVolume());
 	}
 

src/output/plugins/PipeWireOutputPlugin.cxx

@@ -273,7 +273,7 @@ private:
 		pw_thread_loop_signal(thread_loop, false);
 	}
 
-	std::chrono::steady_clock::duration Delay() const noexcept override;
+	[[nodiscard]] std::chrono::steady_clock::duration Delay() const noexcept override;
 	size_t Play(const void *chunk, size_t size) override;
 
 	void Drain() override;