$(AndroidStripILAfterAOT)=true tries to overwrite files it shouldn't

[jonpryor]

Android framework version

net8.0-android, net9.0-android

Affected platform version

.NET 8+

Description

If you build a project with $(RunAOTCompilation)=true and $(AndroidStripILAfterAOT)=true, and .NET is installed into a non-user-writable location (e.g. /usr/local on macOS, owned by root):

dotnet new android -n net9-android-filewrite
cd net9-android-filewrite
dotnet build -bl -p:RunAOTCompilation=true -p:AndroidStripILAfterAOT=true

then the build will fail:

/usr/local/share/dotnet/packs/Microsoft.Android.Sdk.Darwin/35.0.7/targets/Microsoft.Android.Sdk.Aot.targets(142,5):
error MSB3021: Unable to copy file "obj/Debug/net9.0-android/android-x64/stripped/Microsoft.CSharp.dll" to "/usr/local/share/dotnet/packs/Microsoft.NETCore.App.Runtime.Mono.android-x64/9.0.0/runtimes/android-x64/lib/net9.0/Microsoft.CSharp.dll".
Access to the path '/usr/local/share/dotnet/packs/Microsoft.NETCore.App.Runtime.Mono.android-x64/9.0.0/runtimes/android-x64/lib/net9.0/Microsoft.CSharp.dll' is denied.

This is concerning because it could work! I have a separate .NET 8 install in $HOME/Downloads/dotnet-sdk-8.0.206-osx-x64, and building a .NET 8 project with this .NET install with these properties set worked:

$HOME/Downloads/dotnet-sdk-8.0.206-osx-x64/dotnet build -bl -p:RunAOTCompilation=true -p:AndroidStripILAfterAOT=true

The binlog contains:

Moving file from "…/obj/Debug/net8.0-android/android-arm64/aot-in/System.Private.Xml_trimmed.dll" to "$HOME/Downloads/dotnet-sdk-8.0.206-osx-x64/packs/Microsoft.NETCore.App.Runtime.Mono.android-arm64/8.0.11/runtimes/android-arm64/lib/net8.0/System.Private.Xml.dll".

That's bananas.

But wait, it's worse! Try that with a MAUI app -- which pulls in lots of NuGet packages, with assemblies in writable $HOME/.nuget -- and:

Moving file from "…/obj/Debug/net8.0-android/android-arm/aot-in/Xamarin.AndroidX.ExifInterface_trimmed.dll" to "$HOME/.nuget/packages/xamarin.androidx.exifinterface/1.3.6.2/lib/net6.0-android31.0/Xamarin.AndroidX.ExifInterface.dll".

There goes my NuGet cache!

[jonathanpeppers]

$(AndroidStripILAfterAOT) is definitely still in the realm of "experimental", should we put that on a doc somewhere?

[jonpryor]

@jonathanpeppers wrote:

$(AndroidStripILAfterAOT) is definitely still in the realm of "experimental", should we put that on a doc somewhere?

I don't understand. Are you saying that we should document that if $(AndroidStripILAfterAOT)=true builds will hose your NuGet cache and thus corrupt all future builds? (That's quite the thing to only document.)

We should either fix this post haste, or remove support for $(AndroidStripILAfterAOT) (assuming that's the only thing that triggers the file overwrites).

[jonathanpeppers]

I would suspect few are using $(AndroidStripILAfterAOT) (it's not a default setting), so they would have to discover that it exists.

The logic here is optional:

android/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Aot.targets

Lines 134 to 146 in e98d20f

	<ILStrip
	Condition=" '$(AndroidStripILAfterAOT)' == 'true' "
	TrimIndividualMethods="true"
	Assemblies="@(_MonoAOTCompiledAssemblies)"
	IntermediateOutputPath="$(IntermediateOutputPath)"
	DisableParallelStripping="$(_DisableParallelAot)">
	<Output TaskParameter="UpdatedAssemblies" ItemName="_ILStripUpdatedAssemblies" />
	</ILStrip>
	<Copy
	Condition=" '$(AndroidStripILAfterAOT)' == 'true' and '%(_ILStripUpdatedAssemblies.ILStripped)' == 'true' and '%(_ILStripUpdatedAssemblies.UntrimmedAssemblyFilePath)' != '' "
	SourceFiles="@(_ILStripUpdatedAssemblies)"
	DestinationFiles="@(_ILStripUpdatedAssemblies->'%(UntrimmedAssemblyFilePath)')"
	/>

It probably needs to be working against (yet another) folder with a copy of all assemblies.