Find unused Elm record fields

README.md

Find unused Elm record fields

This script finds some unused record fields (but not all).

First run npm ci, and then:

git grep -l '^main =' | xargs elm make --output elm.js && node find-unused-record-fields.js < elm.js

find-unused-record-fields.js

const fs = require("fs");
const jsTokens = require("js-tokens");

const projectPrefix = "$author$project$";

const code = fs.readFileSync(process.stdin.fd, "utf8");

const fields = new Map();
const usedFields = new Set();

let prevPrevPrevToken = { type: "LineTerminatorSequence", value: "\n" };
let prevPrevToken = { type: "LineTerminatorSequence", value: "\n" };
let prevToken = { type: "LineTerminatorSequence", value: "\n" };
let currentProjectFunction = undefined;

for (const token of jsTokens(code)) {
  if (
    prevPrevPrevToken.type === "LineTerminatorSequence" &&
    prevPrevToken.value === "var" &&
    prevToken.type === "WhiteSpace"
  ) {
    if (token.value.startsWith(projectPrefix)) {
      currentProjectFunction = token.value
        .slice(projectPrefix.length)
        .replace(/\$/g, ".");
    } else {
      currentProjectFunction = undefined;
    }
  } else if (
    currentProjectFunction !== undefined &&
    prevPrevToken.type === "IdentifierName" &&
    !prevPrevToken.value.startsWith("_") &&
    prevToken.value === ":" &&
    token.type !== "LineTerminatorSequence"
  ) {
    const name = prevPrevToken.value;
    const previous = fields.get(name);
    if (previous === undefined) {
      fields.set(name, new Set([currentProjectFunction]));
    } else {
      previous.add(currentProjectFunction);
    }
  } else if (prevToken.value === "." && token.type === "IdentifierName") {
    usedFields.add(token.value);
  }
  prevPrevPrevToken = prevPrevToken;
  prevPrevToken = prevToken;
  prevToken = token;
}

for (const [field, functionNames] of fields) {
  if (!usedFields.has(field)) {
    console.log(`${field} in ${Array.from(functionNames).join(", ")}`);
  }
}

package-lock.json

{
  "name": "elm-unused-record-fields",
  "lockfileVersion": 2,
  "requires": true,
  "packages": {
    "": {
      "dependencies": {
        "js-tokens": "8.0.1"
      }
    },
    "node_modules/js-tokens": {
      "version": "8.0.1",
      "resolved": "https://registry.npmjs.org/js-tokens/-/js-tokens-8.0.1.tgz",
      "integrity": "sha512-3AGrZT6tuMm1ZWWn9mLXh7XMfi2YtiLNPALCVxBCiUVq0LD1OQMxV/AdS/s7rLJU5o9i/jBZw/N4vXXL5dm29A=="
    }
  },
  "dependencies": {
    "js-tokens": {
      "version": "8.0.1",
      "resolved": "https://registry.npmjs.org/js-tokens/-/js-tokens-8.0.1.tgz",
      "integrity": "sha512-3AGrZT6tuMm1ZWWn9mLXh7XMfi2YtiLNPALCVxBCiUVq0LD1OQMxV/AdS/s7rLJU5o9i/jBZw/N4vXXL5dm29A=="
    }
  }
}

package.json

{
  "private": true,
  "dependencies": {
    "js-tokens": "8.0.1"
  }
}