MSBuild custom derived build events deprecated
Custom derived build events of any subclass of BuildEventArgs by any build extensibility (mainly custom tasks) have been deprecated.
Previous behavior
Previously, you could derive from any subclass of BuildEventArgs and use those types freely in custom tasks and other build extensibility points.
New behavior
Starting in .NET 8, a build error is issued if your code uses any type derived from BuildEventArgs and you build using the .NET 8 version of MSBuild, that is, from the command line:
Usage of unsecure BinaryFormatter during serialization of custom event type 'MyCustomBuildEventArgs'. This will be deprecated soon. Please use Extended*EventArgs instead. More info: https://aka.ms/msbuild/eventargs
Starting from Visual Studio version 17.10, the same behavior applies to builds in Visual Studio.
Version introduced
.NET 8 RC 1
Type of change
This change is a behavioral change.
Reason for change
BinaryFormatter serialization is obsolete in .NET 8 and later versions. Any use of BinaryFormatter is deamed unsecure and throws an exception at run time. Since MSBuild custom derived build events use BinaryFormatter, your build would crash if you use these events in your build. The new build error provides a more graceful failure.
Recommended action
Use one of the following newly introduced, built-in events for extensibility instead of your custom derived build event:
- ExtendedCustomBuildEventArgs
- ExtendedBuildErrorEventArgs
- ExtendedBuildMessageEventArgs
- ExtendedBuildWarningEventArgs
Alternatively, you can temporarily disable the check by explicitly setting the environment variable MSBUILDCUSTOMBUILDEVENTWARNING to something other than 1.
