function formatMessage()

in packages/annotated/dev-scripts/utils/formatWebpackMessages.js [17:115]

• 73 lines of code
• 14 McCabe index (conditional complexity)

function formatMessage(message) {
  let lines = [];

  if (typeof message === "string") {
    lines = message.split("\n");
  } else if ("message" in message) {
    lines = message["message"].split("\n");
  } else if (Array.isArray(message)) {
    message.forEach((message) => {
      if ("message" in message) {
        lines = message["message"].split("\n");
      }
    });
  }

  // Strip webpack-added headers off errors/warnings
  // https://github.com/webpack/webpack/blob/master/lib/ModuleError.js
  lines = lines.filter((line) => !/Module [A-z ]+\(from/.test(line));

  // Transform parsing error into syntax error
  // TODO: move this to our ESLint formatter?
  lines = lines.map((line) => {
    const parsingError = /Line (\d+):(?:(\d+):)?\s*Parsing error: (.+)$/.exec(
      line
    );
    if (!parsingError) {
      return line;
    }
    const [, errorLine, errorColumn, errorMessage] = parsingError;
    return `${friendlySyntaxErrorLabel} ${errorMessage} (${errorLine}:${errorColumn})`;
  });

  message = lines.join("\n");
  // Smoosh syntax errors (commonly found in CSS)
  message = message.replace(
    /SyntaxError\s+\((\d+):(\d+)\)\s*(.+?)\n/g,
    `${friendlySyntaxErrorLabel} $3 ($1:$2)\n`
  );
  // Clean up export errors
  message = message.replace(
    /^.*export '(.+?)' was not found in '(.+?)'.*$/gm,
    `Attempted import error: '$1' is not exported from '$2'.`
  );
  message = message.replace(
    /^.*export 'default' \(imported as '(.+?)'\) was not found in '(.+?)'.*$/gm,
    `Attempted import error: '$2' does not contain a default export (imported as '$1').`
  );
  message = message.replace(
    /^.*export '(.+?)' \(imported as '(.+?)'\) was not found in '(.+?)'.*$/gm,
    `Attempted import error: '$1' is not exported from '$3' (imported as '$2').`
  );
  lines = message.split("\n");

  // Remove leading newline
  if (lines.length > 2 && lines[1].trim() === "") {
    lines.splice(1, 1);
  }
  // Clean up file name
  lines[0] = lines[0].replace(/^(.*) \d+:\d+-\d+$/, "$1");

  // Cleans up verbose "module not found" messages for files and packages.
  if (lines[1] && lines[1].indexOf("Module not found: ") === 0) {
    lines = [
      lines[0],
      lines[1]
        .replace("Error: ", "")
        .replace("Module not found: Cannot find file:", "Cannot find file:"),
    ];
  }

  // Add helpful message for users trying to use Sass for the first time
  if (lines[1] && lines[1].match(/Cannot find module.+sass/)) {
    lines[1] = "To import Sass files, you first need to install sass.\n";
    lines[1] +=
      "Run `npm install sass` or `yarn add sass` inside your workspace.";
  }

  message = lines.join("\n");
  // Internal stacks are generally useless so we strip them... with the
  // exception of stacks containing `webpack:` because they're normally
  // from user code generated by webpack. For more information see
  // https://github.com/facebook/create-react-app/pull/1050
  message = message.replace(
    /^\s*at\s((?!webpack:).)*:\d+:\d+[\s)]*(\n|$)/gm,
    ""
  ); // at ... ...:x:y
  message = message.replace(/^\s*at\s<anonymous>(\n|$)/gm, ""); // at <anonymous>
  lines = message.split("\n");

  // Remove duplicated newlines
  lines = lines.filter(
    (line, index, arr) =>
      index === 0 || line.trim() !== "" || line.trim() !== arr[index - 1].trim()
  );

  // Reassemble the message
  message = lines.join("\n");
  return message.trim();
}