Remove unused GraphQL fragment

index.ts

import assert from "assert";
import { parse, print, DocumentNode, visit } from "graphql";

function removeUnusedFragment(document: DocumentNode) {
  const usedFragmentSet = new Set<string>();

  // mark used
  visit(document, {
    FragmentSpread(node) {
      usedFragmentSet.add(node.name.value);
    }
  });

  // sweep
  const doc = visit(document, {
    FragmentDefinition(node) {
      if (usedFragmentSet.has(node.name.value)) return;
      return null;
    }
  });

  return doc;
}

const rawDocStr = `
  fragment A on Hoge {
    id
  }

  fragment B on Hoge {
    id
  }

  fragment C on Hoge {
    ...A
  }

  query Query {
    ...C
  }
`;

const rawDocNode = parse(rawDocStr);
const docNode = removeUnusedFragment(rawDocNode);

console.log(print(docNode));

//  fragment A on Hoge {
//    id
//  }
//
//  fragment C on Hoge {
//    ...A
//  }
//
//  query Query {
//    ...C
//  }