ASP.NET Core assemblies should participate in member-level trimming

[mthalman]

When using the TrimMode=Link publish option, none of the ASP.NET Core assemblies are affected. They all remain at their full size even if members within those assemblies are never accessed by a code path in the application.

Because of the quantity and size of the ASP.NET Core assemblies, there is a big opportunity to reduce the size of a deployed app if these assemblies participated in member-level trimming.

As an example, this sample ASP.NET Core application has the following trimmed container image sizes on Alpine Linux:

TrimMode	Size
<Default>	98.5 MB
Link	80 MB

If the ASP.NET Core assemblies participated in assembly-level trimming, this reduction would be even greater.

Repro steps:

1. git clone https://github.com/dotnet/dotnet-docker.git
2. cd dotnet-docker/samples/aspnetapp
3. docker build -t default-trimming -f Dockerfile.alpine-x64-slim .
4. Modify Dockerfile.alpine-x64-slim to include /p:TrimMode=Link in the dotnet publish call
5. docker build -t link-trimming -f Dockerfile.alpine-x64-slim .
6. docker inspect --format "{{ .Size }}" default-trimming
7. docker inspect --format "{{ .Size }}" link-trimming

[mthalman]

cc @davidfowl, @eerhardt

[eerhardt]

Duplicate of #27384?

[davidfowl]

Yes