(UnionTypeDefinition : Description? union Name Directives[Const]? UnionMemberTypes?)

SchemaProblem{errors=[Union type 'Pet' must include one or more member types.]}

import graphql.schema.idl.SchemaParser
import graphql.schema.idl.UnExecutableSchemaGenerator
import org.junit.jupiter.api.Test

/**
 * Demonstrates a graphql-java bug: empty union base definitions with members
 * added via extensions are rejected, even though the GraphQL spec allows this.
 *
 * The spec grammar (UnionTypeDefinition : Description? union Name Directives[Const]? UnionMemberTypes?)
 * makes UnionMemberTypes optional. SchemaParser correctly parses this SDL and
 * TypeDefinitionRegistry correctly shows the union extensions. However,
 * SchemaGenerator.makeExecutableSchema() fails validation with:
 *
 *   SchemaProblem{errors=[Union type 'Pet' must include one or more member types.]}
 *
 * The validation checks the base definition before merging extension members.
 */
class UnionTest {
    @Test
    fun `test empty union base`() {
        val sdl = """
            type Cat { meow: String }
            type Dog { bark: String }
            union Pet
            extend union Pet = Cat | Dog
            type Query { pet: Pet }
        """.trimIndent()

        val registry = SchemaParser().parse(sdl)

        println("=== Registry parsed successfully ===")
        println("Types: ${registry.types().keys}")
        println("Union extensions: ${registry.unionTypeExtensions()}")

        try {
            val schema = UnExecutableSchemaGenerator.makeUnExecutableSchema(registry)
            println("=== Schema built successfully ===")
        } catch (e: Exception) {
            println("=== Exception ===")
            println("Class: ${e.javaClass.name}")
            println("Message: ${e.message}")
            e.printStackTrace()
            throw e
        }
    }
}