[clang-tidy] use nodiscard

Introduced in C++17. It replaces gcc's warn_unused_result.

Found with modernize-use-nodiscard.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/decoder/plugins/DsdiffDecoderPlugin.cxx

@@ -51,7 +51,7 @@ struct DsdiffChunkHeader {
 	 * Read the "size" attribute from the specified header, converting it
 	 * to the host byte order if needed.
 	 */
-	constexpr
+	[[nodiscard]] constexpr
 	uint64_t GetSize() const {
 		return size.Read();
 	}

src/decoder/plugins/MadDecoderPlugin.cxx

@@ -146,10 +146,10 @@ private:
 	void ParseId3(size_t tagsize, Tag *tag) noexcept;
 	MadDecoderAction DecodeNextFrame(bool skip, Tag *tag) noexcept;
 
-	gcc_pure
+	[[nodiscard]] gcc_pure
 	offset_type ThisFrameOffset() const noexcept;
 
-	gcc_pure
+	[[nodiscard]] gcc_pure
 	offset_type RestIncludingThisFrame() const noexcept;
 
 	/**
@@ -168,7 +168,7 @@ private:
 		times = new mad_timer_t[max_frames];
 	}
 
-	gcc_pure
+	[[nodiscard]] gcc_pure
 	size_t TimeToFrame(SongTime t) const noexcept;
 
 	/**

src/decoder/plugins/OpusDecoderPlugin.cxx

@@ -94,7 +94,7 @@ public:
 	/**
 	 * Has DecoderClient::Ready() been called yet?
 	 */
-	bool IsInitialized() const {
+	[[nodiscard]] bool IsInitialized() const {
 		return previous_channels != 0;
 	}
 

src/decoder/plugins/VorbisDecoderPlugin.cxx

@@ -86,7 +86,7 @@ public:
 		return ::CheckAudioFormat(vi.rate, sample_format, vi.channels);
 	}
 
-	AudioFormat CheckAudioFormat() const {
+	[[nodiscard]] AudioFormat CheckAudioFormat() const {
 		return CheckAudioFormat(vi);
 	}
 

src/decoder/plugins/WavpackDecoderPlugin.cxx

@@ -291,7 +291,7 @@ struct WavpackInput {
 
 	int32_t ReadBytes(void *data, size_t bcount);
 
-	InputStream::offset_type GetPos() const {
+	[[nodiscard]] InputStream::offset_type GetPos() const {
 		return is.GetOffset();
 	}
 
@@ -337,14 +337,14 @@ struct WavpackInput {
 		}
 	}
 
-	InputStream::offset_type GetLength() const {
+	[[nodiscard]] InputStream::offset_type GetLength() const {
 		if (!is.KnownSize())
 			return 0;
 
 		return is.GetSize();
 	}
 
-	bool CanSeek() const {
+	[[nodiscard]] bool CanSeek() const {
 		return is.IsSeekable();
 	}
 };