CodeGen error for union _Entity = SomeEntity

[hchen]

Our team is encoutering an issue when generating types from schema if union _Entity = SomeEntity is included in the schema definition. This element is required per Apollo Subgraph specification

Caused by: java.lang.IllegalArgumentException: couldn't make a guess for com.abc.graphql.testgql.types._Entity
        at com.squareup.kotlinpoet.ClassName$Companion.bestGuess(ClassName.kt:205)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.KotlinPoetUtilsKt.ktTypeClassBestGuess(KotlinPoetUtils.kt:281)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.KotlinPoetUtilsKt.toKtTypeName(KotlinPoetUtils.kt:244)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.KotlinPoetUtilsKt.toKtTypeName$default(KotlinPoetUtils.kt:240)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.KotlinTypeUtils.findKtInterfaceName(KotlinTypeUtils.kt:110)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.AbstractKotlinDataTypeGenerator.generate$graphql_dgs_codegen_core(KotlinDataTypeGenerator.kt:266)
        at com.netflix.graphql.dgs.codegen.generators.kotlin.KotlinDataTypeGenerator.generate(KotlinDataTypeGenerator.kt:71)
        at com.netflix.graphql.dgs.codegen.CodeGen$generateKotlinDataTypes$3.invoke(CodeGen.kt:422)
        at com.netflix.graphql.dgs.codegen.CodeGen$generateKotlinDataTypes$3.invoke(CodeGen.kt:420)

However, if we change the target language to Java instead of Kotlin, this issue doesn't occur.

I have logged this issue in kotlinpoet which dgs-codegen uses for codegen.

I'm wondering if anyone else has the same issue? We're using the maven version of the codegen plugin and want to check if this is specific to the maven version.

Thanks in advance for your help.

[hchen]

I have just tested using dgs-federation-example by adding the following to schema.graphqls

scalar _FieldSet
directive @key(fields: _FieldSet!) repeatable on OBJECT | INTERFACE

union _Entity = Show

This will results the same error.

* What went wrong:
Execution failed for task ':generateJava'.
> couldn't make a guess for com.example.demo.generated.types._Entity

[hchen]

After further investigation it turns out there is no need to add union _Entity = SomeEntity in the schema. The framework will automatically generate.