.NET 7 Android TrimmerRootDescriptor vs TrimmerRootAssembly

[akravch]

Environment

.NET 7.0.102, Android workload 33.0.26/7.0.100

Scenario

I encountered the issue similar to what's described here: JamesNK/Newtonsoft.Json#2802, so I'll just use it as an example.

So there is an issue with the following code if you run it on a trimmed Android app:

var tuple = new Tuple<decimal, string>(1, "one");
var json = JsonConvert.SerializeObject(tuple);

It throws an exception which is clearly a result of the trimming process:

Newtonsoft.Json.JsonSerializationException: A member with the name '' already exists on 'System.Tuple`2[System.Decimal,System.String]'. Use the JsonPropertyAttribute to specify another name.
...

I would expect this to be solved by adding the System.Private.CoreLib assembly into the trimmer exclusions by adding the following into the .csproj:

<ItemGroup>
  <TrimmerRootDescriptor Include="MyRoots.xml" />
</ItemGroup>

... and the following into the MyRoots.xml file:

<linker>
  <assembly fullname = "System.Private.CoreLib" preserve="all" />
</linker>

Unfortunatelly, this doesn't fix the issue, although it definitely changes things for the System.Private.CoreLib - I can see that the resulting assembly size is now larger, which means the configuration has been applied.

Workarounds

1. Setting <IsTrimmable>false</IsTrimmable> for the assembly as described here: Android .net6 project throw exception when serilaize Tuple in Release mode (v13.0.2) JamesNK/Newtonsoft.Json#2802 (comment)
2. Adding <TrimmerRootAssembly Include="System.Private.CoreLib" /> into the .csproj

I went with the latter for now since it's more neat, but to be honest, I don't understand why does it not work in the same way as TrimmerRootDescriptor. In my mind it's supposed to be fully equivalent to the preserve="all" attribute.

Question

So is it a configuration bug or is this behavior by design? And which way should one choose to exclude something from the trimming process completely after all?

@dotnet/illink-contrib a new issue has been filed in the ILLink area, please triage

[vitek-karas]

@sbomer could you please take a quick look why the behaviors are different?

[sbomer]

I wasn't able to reproduce this in a console app, so this may be specific to android. @akravch thank you for the report - are you able to reproduce this kind of issue in a console app? Would you be able to share the trimmed System.Private.CoreLib that produces the issue for you?

[akravch]

@sbomer thanks for such a quick response.
Attaching the .dll and .so files for different configurations: System.Private.CoreLib.zip

I can see that the .dll size is equal to the untrimmed lib size only when I use TrimmerRootAssembly. This is also the only case, except for the no trim case, in which the app does not crash.

I have also pushed my repro code here: https://github.com/akravch/NewtonsoftJsonNet7, so you may as well check it out. Each case is a separate solution configuration.

Please let me know if there's anything else I can provide to help.

[michaelhannes]

I had just recently moved from .net 5 to .net 6 ( had problem with 6.0.16) and then .net 7

i am having what seemed to be same problem, with returning a tuple from api to Blazor WASM client, having an (bool,string) where string was empty. but it only fails when deploying to Azure webapp, running locally works fine.

var result = await _httpClient.GetFromJsonAsync<Tuple<bool, string>>(apiPath);

Error: ConstructorContainsNullParameterNames, System.Tuple`2[System.Boolean,System.String] (anonymous) @ blazor.webassembl

When I change the httpClient call to GetStringAsync and try to parse the JSON (using both newtonsoft or system.text.json (?) - then an error occurs during deserialization.

sorry for the convoluted message.

[akravch]

A little update from my side: still facing it on 7.0.302.

Had the same issue serializing a simple anonymous type like new { a = 1, b = 2 }. Worked around it by not only including System.Private.CoreLib as a TrimmerRootAssembly, but doing the same thing for the assembly where the type is defined.