[Breaking change]: Resolving collectible assembly into a non-collectible AssemblyLoadContext now throws #29200
Description
Description
We were incorrectly allowing resolving collectible assemblies into a non-collectible AssemblyLoadContext. That may seemingly work ok in some cases and lead to runtime crashes or unexpected NullReferenceException in others.
The change in dotnet/runtime#68550 prevents that incorrect behavior by throwing an exception when the AssemblyLoadContext.Load or the AssemblyLoadContext.Resolving event returns a collectible Assembly and the AssemblyLoadContext is non-collectible.
Version
.NET 7 Preview 5
Previous behavior
Returning a collectible Assembly in the AssemblyLoadContext.Load override or the AssemblyLoadContext.Resolving event of a non-collectible AssemblyLoadContext doesn't cause any exceptions to be thrown.
New behavior
Returning a collectible Assembly in the AssemblyLoadContext.Load override or the AssemblyLoadContext.Resolving event of a non-collectible AssemblyLoadContext results in throwing a System.IO.FileLoadException with System.NotSupportedException inner exception.
Type of breaking change
- Binary incompatible: Existing binaries may encounter a breaking change in behavior, such as failure to load/execute or different run-time behavior.
- Source incompatible: Source code may encounter a breaking change in behavior when targeting the new runtime/component/SDK, such as compile errors or different run-time behavior.
Reason for change
This change fixes a bug. The collectible Assembly would be collected while the AssemblyLoadContext that has a reference to it is alive for the rest of the process lifetime. So if the code running in that context references anything from that Assembly after it is collected, it would crash the runtime or result in unexpected NullReferenceException, possibly even AccessViolationException and possibly other kinds of bad behavior.
Recommended action
Don't return collectible assemblies in AssemblyLoadContext.Load overload or AssemblyLoadContext.Resolving event of a non-collectible AssemblyLoadContext. Possible workaround is to change the AssemblyLoadContext to collectible by passing true in the isCollectible argument to its constructor and then keep a reference to that AssemblyLoadContext forever to make sure it is never collected.
Feature area
Core .NET libraries
Affected APIs
AssemblyLoadContext.Load override
AssemblyLoadContext.Resolving event