How to use the apollo-graphql.buildSchemaFromSDL function in apollo-graphql

}
            : null,
        )
        .filter(isNotNullOrUndefined);

      keyDirectiveInfoOnTypeExtensions.push(...keyDirectivesInfo);
    },
  });

  // this allows us to build a partial schema
  let schema = new GraphQLSchema({
    query: undefined,
    directives: [...specifiedDirectives, ...federationDirectives],
  });
  try {
    schema = buildSchemaFromSDL(typeDefs, schema);
  } catch (e) {
    errors.push(e);
    return errors;
  }

  const typeInfo = new TypeInfo(schema);

  for (const { typeName, keyArgument } of keyDirectiveInfoOnTypeExtensions) {
    const keyDirectiveSelectionSet = parse(
      `fragment __generated on ${typeName} { ${keyArgument} }`,
    );
    visit(
      keyDirectiveSelectionSet,
      visitWithTypeInfo(typeInfo, {
        Field() {
          const fieldDef = typeInfo.getFieldDef();

if ('typeDefs' in modulesOrSDL) {
    const { typeDefs, resolvers } = modulesOrSDL;
    const augmentedTypeDefs = Array.isArray(typeDefs) ? typeDefs : [typeDefs];
    shapedModulesOrSDL = augmentedTypeDefs.map((typeDefs, i) => {
      const module: GraphQLSchemaModule = { typeDefs };
      // add the resolvers to the first "module" in the array
      if (i === 0 && resolvers) module.resolvers = resolvers;
      return module;
    });
  } else {
    shapedModulesOrSDL = modulesOrSDL;
  }

  const modules = modulesFromSDL(shapedModulesOrSDL);

  let schema = buildSchemaFromSDL(
    modules,
    new GraphQLSchema({
      query: undefined,
      directives: [...specifiedDirectives, ...federationDirectives],
    }),
  );

  // At this point in time, we have a schema to be printed into SDL which is
  // representative of what the user defined for their schema. This is before
  // we process any of the federation directives and add custom federation types
  // so its the right place to create our service definition sdl.
  //
  // We have to use a modified printSchema from graphql-js which includes
  // support for preserving the *uses* of federation directives while removing
  // their *definitions* from the sdl.
  const sdl = printSchema(schema);

// load each path and get sdl string from each, if a list, concatenate them all
    const documents = path
      ? [this.loadFileAndGetDocument(path)]
      : paths
      ? paths.map(this.loadFileAndGetDocument, this)
      : undefined;

    if (!documents)
      throw new Error(
        `Schema could not be loaded for [${
          path ? path : paths ? paths.join(", ") : "undefined"
        }]`
      );

    this.schema = buildSchemaFromSDL(documents);

    if (!this.schema) throw new Error(`Schema could not be loaded for ${path}`);
    return this.schema;
  }