Unexpected code size increase when using JSON Source Generator

[mrange]

Hi.

I tried the JSON Source Generator as asked too. I was surprised to find that my assembly grew from 7 KiB to 125 KiB after adding source generators even though I only generated code for Person and List<Person>.

  public partial record Person
  {
    public int                  Id                             { get; set; }
    public string               FirstName                      { get; set; }
    public string               LastName                       { get; set; }
  }

  [JsonSerializable(typeof(Person)      , GenerationMode = default)]
  [JsonSerializable(typeof(List<Person>), GenerationMode = default)]
  partial class MyJsonContext : JsonSerializerContext
  {
  }

When looking at the generated code I found a bunch of generated methods that I didn't use and that should be possible to have in a shared library such AssemblySerialize.

It's not really a bug but I felt 120 KiB was a bit too much, especially in a world where we try to squeeze down the size for Blazor WASM Clients.

I wrote a bit about my experience with using JSON source generator here: https://github.com/mrange/T4JsonSerializer

Regards,
Mårten

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Issue Details

---

Hi.

I tried the JSON Source Generator as asked too. I was surprised to find that my assembly grew from 7 KiB to 125 KiB after adding source generators even though I only generated code for Person and List<Person>.

  public partial record Person
  {
    public int                  Id                             { get; set; }
    public string               FirstName                      { get; set; }
    public string               LastName                       { get; set; }
  }

  [JsonSerializable(typeof(Person)      , GenerationMode = default)]
  [JsonSerializable(typeof(List<Person>), GenerationMode = default)]
  partial class MyJsonContext : JsonSerializerContext
  {
  }

When looking at the generated code I found a bunch of generated methods that I didn't use and that should be possible to have in a shared library such AssemblySerialize.

It's not really a bug but I felt 120 KiB was a bit too much, especially in a world where we try to squeeze down the size for Blazor WASM Clients.

I wrote a bit about my experience with using JSON source generator here: https://github.com/mrange/T4JsonSerializer

Regards,
Mårten

Author:	mrange
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[layomia]

Thanks for the feedback & analysis of the generator's performance. I believe the size issue is resolved following #56354. The generator was including a bunch of auto-generated members on record types, but those should now be excluded following this PR. You'll be able to try the fix in a couple hours when we have a new build of System.Text.Json - https://dev.azure.com/dnceng/public/_packaging?_a=package&feed=dotnet6&view=versions&package=System.Text.Json&version=6.0.0-rc.1.21406.4&protocolType=NuGet. Pls let us know if the issue is resolved.

[mrange]

@layomia Hi. Tried it but after updating the reference my code no longer compiles. It almost seems like the source generator hasn't generated any code as it complains that: error CS0534: 'MyJsonContext' does not implement inherited abstract member 'JsonSerializerContext.GetTypeInfo(Type)'

I tried faking the method but then I got other errors.

It could be because you made some changes to how to use the source generator but I wasn't aware of those.

If you are interested see my PR: https://github.com/mrange/T4JsonSerializer/pull/1/files#diff-7f0adf85cf5c2c4802b4e4849b49eb3fd63de1852d53df61da98fadf46604e6fR10

(It also seems the new version has updated transitive dependencies but I downloaded them as well so I hope that's good)

[mrange]

I also tried the version you linked but with the same results.

[mrange]

Tried system.text.json.6.0.0-rc.1.21409.2 as well and still seems to me that the source generator isn't executed. Perhaps I am doing something wrong?

[am11]

@mrange, could you try with the daily build of whole sdk / shared framework (https://github.com/dotnet/installer#installers-and-binaries first column in the table)?

On my Ubuntu box, I did:

mkdir ~/.dotnet6
curl -sSL https://aka.ms/dotnet/6.0/daily/dotnet-sdk-linux-x64.tar.gz | tar xzf - -C ~/.dotnet6
~/.dotnet6/dotnet --version
# 6.0.100-rc.1.21409.2

cd T4JsonSerializer/src
cat > nuget.config <<EOF
<configuration>
  <packageSources>
    <add key="dotnet6" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json" />
  </packageSources>
</configuration>
EOF

~/.dotnet6/dotnet publish -c Release -r linux-x64 --self-contained

it cuts down the size from (128K and 8.0K from last week's build) to:

16K	CsSourceGeneratorsJson.dll
8.0K	CsNoSourceGeneratorsJson.dll

[mrange]

Thanks for the tips, I managed to build it on Ubuntu in WSL and when inspecting the binaries it looks much better. I no longer see AssemblyWrite and other unrelated metadata. There is metadata generated for Int32 and String which I guess could be in a common assembly but it doesn't take much space.

[danmoseley]

@mrange now you have it working, we'd value any other feedback you may have (if bugs/suggestions then probably as different issues)

Would it make sense to close this one now?

[mrange]

Feel free to close this one.