Annotate return values with nodiscard

Add nodiscard to functions returning values that should not be
ignored, such as accessors and lock wrappers.  This helps prevent
subtle bugs by alerting developers when important return values are
discarded.

Author: mizdebsk

src/java_symbols.hpp

@@ -68,7 +68,7 @@ struct Path_origin_entry : std::filesystem::path
 	{
 	}
 
-	std::string_view origin() const noexcept
+	[[nodiscard]] std::string_view origin() const noexcept
 	{
 		return origin_;
 	}
@@ -100,7 +100,7 @@ struct Mutex
 		return Locked(value_, mutex_);
 	}
 
-	Locked<const Type, std::mutex> lock() const
+	[[nodiscard]] Locked<const Type, std::mutex> lock() const
 	{
 		return Locked(value_, mutex_);
 	}