Improper handling of cyclical directive defs (spec issue) #4201

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

import static org.junit.jupiter.api.Assertions.assertThrows;

/**
 * Reproduction test for graphql-java circular directive dependency bug.
 *
 * When directives mutually reference each other via applied directives on their
 * arguments, UnExecutableSchemaGenerator.makeUnExecutableSchema() throws
 * StackOverflowError instead of detecting the cycle and reporting a proper error.
 *
 * NOTE: graphql-java correctly detects direct self-reference (A -> A) and throws
 * SchemaProblem, but fails to detect indirect cycles (A -> B -> A) or longer
 * cycles (A -> B -> C -> A), resulting in StackOverflowError.
 *
 * Dependencies: graphql-java, JUnit 5
 */
public class CircularDirectiveStackOverflowTest {

    @Test
    void selfReferencingDirectiveCorrectlyThrowsSchemaProblem() {
        // A directive that references itself via applied directive on its argument
        // graphql-java correctly detects this direct self-reference
        String sdl = """
            directive @recursive(depth: Int @recursive(depth: 0)) on FIELD_DEFINITION | ARGUMENT_DEFINITION

            type Query { field: String @recursive(depth: 5) }
            """;

        TypeDefinitionRegistry registry = new SchemaParser().parse(sdl);

        // This correctly throws SchemaProblem (not a bug)
        assertThrows(graphql.schema.idl.errors.SchemaProblem.class, () -> {
            UnExecutableSchemaGenerator.makeUnExecutableSchema(registry);
        });
    }

    @Test
    void mutualDirectiveReferenceCausesStackOverflowError() {
        // Two directives that reference each other via applied directives on arguments
        // This is an indirect cycle: @foo -> @bar -> @foo
        String sdl = """
            directive @foo(x: Int @bar(y: 1)) on FIELD_DEFINITION | ARGUMENT_DEFINITION
            directive @bar(y: Int @foo(x: 2)) on FIELD_DEFINITION | ARGUMENT_DEFINITION

            type Query { field: String @foo(x: 10) @bar(y: 20) }
            """;

        TypeDefinitionRegistry registry = new SchemaParser().parse(sdl);

        // BUG: This throws StackOverflowError instead of a proper validation error
        assertThrows(StackOverflowError.class, () -> {
            UnExecutableSchemaGenerator.makeUnExecutableSchema(registry);
        });
    }

    @Test
    void threeWayCircularDirectiveReferenceCausesStackOverflowError() {
        // Three directives forming a cycle: @dirA -> @dirB -> @dirC -> @dirA
        String sdl = """
            directive @dirA(x: Int @dirB(y: 1)) on FIELD_DEFINITION | ARGUMENT_DEFINITION
            directive @dirB(y: Int @dirC(z: 2)) on FIELD_DEFINITION | ARGUMENT_DEFINITION
            directive @dirC(z: Int @dirA(x: 3)) on FIELD_DEFINITION | ARGUMENT_DEFINITION

            type Query { field: String @dirA(x: 10) @dirB(y: 20) @dirC(z: 30) }
            """;

        TypeDefinitionRegistry registry = new SchemaParser().parse(sdl);

        // BUG: This throws StackOverflowError instead of a proper validation error
        assertThrows(StackOverflowError.class, () -> {
            UnExecutableSchemaGenerator.makeUnExecutableSchema(registry);
        });
    }
}