apply-ts-expect-error.js

README.md

For each tsc error, this adds a comment:

// TODO: Resolve type error
// @ts-expect-error
...

For each Unused '@ts-expect-error' directive error it removes the @ts-expect-error comment as well as any TODO: comment above.

Usage:

tsc --noEmit | node add-ts-expect-error.js

apply-ts-expect-error.js

import { readFileSync, writeFileSync } from "fs";

/**
 * Parses tsc stdout lines into error objects.
 */
function parseTsErrors(content) {
  return [
    ...content.matchAll(
      /^(?<file>[^\( ]+)\((?<lineNr>\d+),(?<columnNr>\d+)\): error TS(?<code>\d+): (?<description>.*)/gm,
    ),
  ].map(({ groups: { file, lineNr, columnNr, code, description } }) => ({
    file,
    lineNr: parseInt(lineNr, 10),
    columnNr: parseInt(columnNr, 10),
    code: parseInt(code, 10),
    description,
  }));
}

/**
 * Deduplicates an array of items by a key function.
 * Returns the first occurrence of each unique key.
 */
function uniqueBy(items, keyFn) {
  return [...new Map(items.map((value) => [keyFn(value), value])).values()];
}

const content = readFileSync(0, "utf-8");

const fileErrors = Object.entries(
  Object.groupBy(parseTsErrors(content), ({ file }) => file),
).map(([file, errors]) => [
  file,
  // Ignore multiple errors on the same line. Only pick the first one.
  uniqueBy(errors, ({ file, lineNr }) => lineNr)
    // Sort the errors by line number in descending order.
    // Having them in descending order helps with making changes. The line numbers remain valid.
    .toSorted((a, b) => b.lineNr - a.lineNr),
]);
for (const [file, errors] of fileErrors) {
  const content = readFileSync(file, "utf-8");
  const lines = content.split("\n");

  for (const { lineNr, code } of errors) {
    const lineIndex = lineNr - 1;
    const line = lines[lineIndex];
    const indentation = line.match(/^\s*/)[0];

    function log(message) {
      console.log(`${file}:${lineNr}: ${message}`);
    }

    if (code === 2578) {
      // Remove @ts-expect-error for TS2578.
      // TS2578: Unused '@ts-expect-error' directive.
      // Sanity check.
      if (!/^\s*\/\/\s*@ts-expect-error/.test(line)) {
        log("Expected // @ts-expect-error directive");
        continue;
      }
      // Also remove TODO comments above @ts-expect-error.
      if (/^\s*\/\/\s*TODO:/.test(lines[lineIndex - 1])) {
        log("Removed unused @ts-expect-error and TODO comment");
        lines.splice(lineIndex - 1, 2);
      } else {
        log("Removed unused @ts-expect-error");
        lines.splice(lineIndex, 1);
      }
    } else {
      // Add @ts-expect-error for all other errors.
      log("Added @ts-expect-error");
      lines.splice(lineIndex, 0, `${indentation}// @ts-expect-error`);
      lines.splice(lineIndex, 0, `${indentation}// TODO: Resolve type error`);
      break;
    }
  }

  const newContent = lines.join("\n");
  writeFileSync(file, newContent, "utf-8");
}