/** @category Validation Rules */
import type { ASTVisitor } from "../../language/visitor.mjs";
import type { SDLValidationContext } from "../ValidationContext.mjs";
/**
 * Unique directive names
 *
 * A GraphQL document is only valid if all defined directives have unique names.
 * @param context - The validation context used while checking the document.
 * @returns A visitor that reports validation errors for this rule.
 * @example
 * ```ts
 * import { buildSchema } from 'graphql';
 * import { UniqueDirectiveNamesRule } from 'graphql/validation';
 *
 * const invalidSDL = `
 *   directive @tag on FIELD directive @tag on QUERY type Query { name: String }
 * `;
 *
 * UniqueDirectiveNamesRule.name; // => 'UniqueDirectiveNamesRule'
 * buildSchema(invalidSDL); // throws an error
 *
 * const validSDL = `
 *   directive @tag on FIELD type Query { name: String }
 * `;
 *
 * buildSchema(validSDL); // does not throw
 * ```
 */
export declare function UniqueDirectiveNamesRule(context: SDLValidationContext): ASTVisitor;