@theguild/federation-composition/esm/subgraph/validation/rules/lone-schema-definition-rule.js

Open Source Composition library for Apollo Federation

import { GraphQLError } from "graphql";
export function LoneSchemaDefinitionRule(context) {
    let schemaDefinitionsCount = 0;
    return {
        SchemaDefinition() {
            if (schemaDefinitionsCount > 0) {
                context.reportError(new GraphQLError("Must provide only one schema definition.", {
                    extensions: {
                        code: "INVALID_GRAPHQL",
                    },
                }));
            }
            ++schemaDefinitionsCount;
        },
    };
}