"Cannot convert error" in generated StrawberryShake code for implemented result types

Is there an existing issue for this?

• I have searched the existing issues

Product

Strawberry Shake

Describe the bug

In a recent project encountered "cannot convert from" error in the StrawberryShake generated code. I simplified the data structure which is handled with errors in the StrawberryShake generator.

There is a base type (ParentType), that is used in one mutation result (MutationResultVariantA) and the there is a extended type (ParentVariant), which is used in the second mutation result (MutationResultVariantB).
Additional data that is inside these types were stripped for simplicity.

The generated error:
cannot convert from 'ConsoleApp1.State.IParentTypeData' to 'ConsoleApp1.State.ParentVariantData'

Steps to reproduce

1. mutations.graphql:

mutation mutationOneTest {
  testMutation {
    parent {
      someValue
    }
  }
}

mutation mutationOne {
  testMutation {
    ... on MutationResultVariantB {
      parent {
        ... on ParentVariant {
          someValue
        }
      }
    }
  }
}

2. schema.graphql:

schema {
  query: Query
  mutation: Mutation
}

type Query {
  testQuery(): MutationResult!
}

type Mutation {
  testMutation(): MutationResult!
}

interface MutationResult {
  parent: ParentType!
}

interface ParentType {
  someValue: Int!
}

type MutationResultVariantA implements MutationResult {
  parent: ParentType!
}

type MutationResultVariantB implements MutationResult {
  parent: ParentVariant!
}

type ParentVariant implements ParentType {
  someValue: Int!
}

3. .graphqlrc,json

{
    "schema": "schema.graphql",
    "documents": "**/*.graphql",
    "extensions": {
        "strawberryShake": {
            "name": "GraphQLClient",
            "dependencyInjection": true,
            "strictSchemaValidation": true,
            "hashAlgorithm": "md5",
            "useSingleFile": true,
            "requestStrategy": "Default",
            "outputDirectoryName": "Generated",
            "noStore": false,
            "emitGeneratedCode": true,
            "razorComponents": false,
            "records": {
                "inputs": false,
                "entities": false
            },
            "transportProfiles": [
                {
                    "default": "Http",
                    "subscription": "WebSocket"
                }
            ]
        }
    }
}

4. Run the generator
5. There is a repo with the bug present: https://github.com/maris-jurgenbergs/SBSGQLBug

Relevant log output

No response

Additional Context?

No response

Version

12.18.0

Reproduce the failure with the linked SBSGQLBug repository using mutations.graphql, schema.graphql, and .graphqlrc.json, then run the StrawberryShake generator. Inspect the generated code for the two mutation results and the ParentType/ParentVariant selection. Done means generation succeeds without the reported cannot-convert error for both mutations.