Another utility that I am bound to reuse between open-source projects. (I'll consider making a package combining my shared utilities in due time.) Here is the code with JSDoc comments:

/**
 * Gets the ESLint-generated `SourceCode` object of a file from its absolute path.
 * @param {string} absolutePath The absolute path of the file.
 * @param {Object} [options] The additional options as follows:
 * @param {import('eslint').Linter} [options.linter] The Linter instance used to retrieve the `SourceCode` object, defaulting to a `new Linter()` per operation, ensuring each instance of the function is based on its own linter (just in case somehow some linters were to run concurrently).
 * @param {import('eslint').Linter.LanguageOptions} [options.languageOptions] The `languageOptions` object used by `linter.verify()`, defaulting to a version that is TypeScript- and JSX-compatible.
 * @returns The ESLint-generated `SourceCode` object of the file, from which the AST (`sourceCode.ast`) and all comments (`sourceCode.getAllComments()`) can be extracted. `null` when encountering fatal syntax.
 */
export const getSourceCodeFromFilePath = (
  absolutePath,
  { languageOptions = typeScriptAndJSXCompatible, linter = new Linter() } = {}
) => {
  // the raw code of the file at the end of the absolute path
  const text = fs.readFileSync(absolutePath, "utf8");
  // utilizes linter.verify ...
  linter.verify(text, { languageOptions });
  // ... to retrieve the raw code as a SourceCode object
  const sourceCode = linter.getSourceCode();

  if (!sourceCode) return null;
  else return sourceCode;
};