[assembly-preparer] PrepareAssemblies + link all (Full trim) fails: IL2036 Unresolved type 'Foundation.NSExpression' in DynamicDependencyAttribute

[rolfbjarne]

Summary

Building an app with PrepareAssemblies=true (the assembly-preparer) and link mode "all" (MtouchLink=Full / TrimMode=full) fails during ILLink with:

error IL2036: <Module>..cctor(): Unresolved type 'Foundation.NSExpression' in 'DynamicDependencyAttribute'.
error NETSDK1144: Optimizing assemblies for size failed.

The assembly-preparer adds a [DynamicDependency] attribute (on the module <Module>..cctor) referencing Foundation.NSExpression, but ILLink then trims NSExpression away in full-link mode, leaving the dependency dangling → IL2036 → the trimmer aborts with NETSDK1144.

Steps to reproduce

Build monotouch-test for iOS with link all + PrepareAssemblies:

tests-monotouch ios --variations='release|linkall' --build-arguments='/p:PrepareAssemblies=true /p:PostProcessAssemblies=true'

or directly:

dotnet build tests/monotouch-test/dotnet/iOS/monotouch-test.csproj -c Release \
  -p:RuntimeIdentifier=iossimulator-arm64 -p:UseFloatingTargetPlatformVersion=true \
  -p:MtouchLink=Full -p:UseMonoRuntime=true \
  -p:PrepareAssemblies=true -p:PostProcessAssemblies=true

Actual result

The build fails:

<Module>..cctor(): Unresolved type 'Foundation.NSExpression' in 'DynamicDependencyAttribute'. (IL2036)
Optimizing assemblies for size failed. (NETSDK1144)

Expected result

The build succeeds, as it does with MtouchLink=SdkOnly and with link None.

Additional context

• Reproduces on main (commit 8111cb6c59) — this is not a regression from any in-flight assembly-preparer change.
• release|linksdk (SdkOnly) + PrepareAssemblies, and link None + PrepareAssemblies, both build and pass monotouch-test (3675 tests, 0 failed).
• A trivial app (MySimpleApp) with MtouchLink=Full + PrepareAssemblies builds fine — the failure only shows up with a larger app (monotouch-test).