fragment-linter.kt

  @Test
  fun validate() {
    val schemaString = """
      type Query {
        user: User!
      }
      
      type User {
        firstName: String!
        lastName: String!
        email: String!
      }
    """.trimIndent()

    val queryString = """
      query GetUser {
        user {
          firstName
          lastName
          email
        }
      }
    """.trimIndent()
    val schema = schemaString.buffer().toSchema()

    val operation = queryString.buffer().parseAsGQLDocument().value?.definitions?.first() as? GQLOperationDefinition ?: error("no operation found")

    validate(schema, operation.selectionSet, "Query", "data")
  }

  private fun validate(schema: Schema, selectionSet: GQLSelectionSet, parentType: String, path: String) {
    val fieldNames: Set<String> = selectionSet.selections.filterIsInstance<GQLField>().map { it.name }.toSet()
    if (fieldNames.contains("firstName")
        && fieldNames.contains("lastName")
        && fieldNames.contains("email")
        && parentType == "User"
    ) {
      error("operation should use fragment ...userFragment instead of querying individual fields at: $path")
    }

    selectionSet.selections.forEach {
      when (it) {
        is GQLField -> {
          if (it.selectionSet != null) {
            val fieldDefinition = it.definitionFromScope(schema, parentType) ?: error("cannot find field definition for ${it.name} at $path")
            validate(schema, it.selectionSet!!, fieldDefinition.type.leafType().name, "${path}.${it.responseName()}")
          }
        }
      }
    }
  }