Description

rstata

opened on Jan 4, 2026

Issue body actions

Describe the bug

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.]}

Root cause is that the validation checks the base definition before merging extension members (which isn't done for other types like interfaces). For deeper dive on root cause see this link.

(GraphQL Java 25.0)

To Reproduce

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
        }
    }
}

Activity

1. rstata commented on Jan 4, 2026

   

   rstata

   on Jan 4, 2026

   Author

   More actions

   Java rewrite:

   import graphql.schema.idl.SchemaParser;
   import graphql.schema.idl.TypeDefinitionRegistry;
   import graphql.schema.idl.UnExecutableSchemaGenerator;
   import org.junit.jupiter.api.Test;
   
   class UnionTest {
   
     /**
      * Demonstrates a graphql-java bug: empty union base definitions with members
      * added via extensions are rejected, even though the GraphQL spec allows this.
      *
      * Expected failure (current graphql-java behavior):
      *
      *   SchemaProblem{errors=[Union type 'Pet' must include one or more member types.]}
      */
     @Test
     void testEmptyUnionBase() {
       String sdl = String.join("\n",
           "type Cat { meow: String }",
           "type Dog { bark: String }",
           "union Pet",
           "extend union Pet = Cat | Dog",
           "type Query { pet: Pet }"
       );
   
       TypeDefinitionRegistry registry = new SchemaParser().parse(sdl);
   
       System.out.println("=== Registry parsed successfully ===");
       System.out.println("Types: " + registry.types().keySet());
       System.out.println("Union extensions: " + registry.unionTypeExtensions());
   
       try {
         UnExecutableSchemaGenerator.makeUnExecutableSchema(registry);
         System.out.println("=== Schema built successfully ===");
       } catch (Exception e) {
         System.out.println("=== Exception ===");
         System.out.println("Class: " + e.getClass().getName());
         System.out.println("Message: " + e.getMessage());
         e.printStackTrace();
         throw e;
       }
     }
   }
   
2. github-actions commented on Mar 5, 2026

   

   github-actionsBot

   on Mar 5, 2026 – with GitHub Actions

   Contributor

   More actions

   Hello, this issue has been inactive for 60 days, so we're marking it as stale. If you would like to continue this discussion, please comment within the next 30 days or we'll close the issue.
3. github-actions

   added

   Stale

   on Mar 5, 2026
4. dondonz

   added 2 commits that reference this issue on Mar 9, 2026

   Fix #4200: Allow empty union base definitions when extensions add mem…

   This issue will close once commit f740eb7 is merged into the 'master' branch.

   f740eb7

   Fix #4200: Allow empty union definitions when extensions provide members

   This issue will close once commit 6989cde is merged into the 'master' branch.

   6989cde
5. github-actions commented on Apr 4, 2026

   

   github-actionsBot

   on Apr 4, 2026 – with GitHub Actions

   Contributor

   More actions

   Hello, as this issue has been inactive for 90 days, we're closing the issue. If you would like to resume the discussion, please create a new issue.
6. github-actions

   closed this as not plannedon Apr 4, 2026
7. andimarek

   reopened this on Apr 4, 2026
8. github-actions

   removed

   Stale

   on Apr 5, 2026
9. dondonz

   added a commit that references this issue on Apr 5, 2026

   Fix #4364 and #4200: nullable type bound and empty union extension su…

   7a3a541
10. andimarek

    closed this as completedin #4388on May 20, 2026
11. andimarek commented on May 20, 2026

    

    andimarek

    on May 20, 2026

    Member

    More actions

    This is fixed in #4388

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