app/@overflow/core/source-map-support.ts

import * as Path from 'path';
import * as Fs from 'fs';
import * as sourceMapSupport from 'source-map-support';

/**
 * This array tells the source map logic which files that we can expect to
 * be able to resolve a source map for and they should reflect the chunks
 * entry names from our webpack config.
 *
 * Note that we explicitly don't enable source maps for the crash process
 * since it's possible that the error which caused us to spawn the crash
 * process was related to source maps.
 */
const knownFilesWithSourceMap = ['renderer.js', 'main.js'];

function retrieveSourceMap(source: string) {
  const fileUriToPath: (uri: string) => string = require('file-uri-to-path');

  // This is a happy path in case we know for certain that we won't be
  // able to resolve a source map for the given location.
  if (!knownFilesWithSourceMap.some(file => source.endsWith(file))) {
    return null;
  }

  // We get a file uri when we're inside a renderer, convert to a path
  if (source.startsWith('file://')) {
    source = fileUriToPath(source);
  }

  // We store our source maps right next to the bundle
  const path = `${source}.map`;

  if (__DEV__ && path.startsWith('http://')) {
    try {
      const xhr = new XMLHttpRequest();
      xhr.open('GET', path, false);
      xhr.send(null);
      if (xhr.readyState === 4 && xhr.status === 200) {
        return { url: Path.basename(path), map: xhr.responseText };
      }
    } catch (error) {
      return;
    }
    return;
  }

  // We don't have an option here, see
  //  https://github.com/v8/v8/wiki/Stack-Trace-API#customizing-stack-traces
  // This happens on-demand when someone accesses the stack
  // property on an error object and has to be synchronous :/
  // eslint-disable-next-line no-sync
  if (!Fs.existsSync(path)) {
    return;
  }

  try {
    // eslint-disable-next-line no-sync
    const map = Fs.readFileSync(path, 'utf8');
    return { url: Path.basename(path), map };
  } catch (error) {
    return;
  }
}

/** A map from errors to their stack frames. */
const stackFrameMap = new WeakMap<Error, ReadonlyArray<any>>();

/**
 * The `prepareStackTrace` that comes from the `source-map-support` module.
 * We'll use this when the user explicitly wants the stack source mapped.
 */
let prepareStackTraceWithSourceMap: (
  error: Error,
  frames: ReadonlyArray<any>
) => string;

/**
 * Capture the error's stack frames and return a standard, un-source mapped
 * stack trace.
 */
function prepareStackTrace(error: Error, frames: ReadonlyArray<any>) {
  stackFrameMap.set(error, frames);

  // Ideally we'd use the default `Error.prepareStackTrace` here but it's
  // undefined so V8 must doing something fancy. Instead we'll do a decent
  // impression.
  return error + frames.map(frame => `\n    at ${frame}`).join('');
}

/** Enable source map support in the current process. */
export function enableSourceMaps() {

  sourceMapSupport.install({
    environment: 'node',
    handleUncaughtExceptions: false,
    retrieveSourceMap,
  });

  const AnyError = Error as any;
  // We want to keep `source-map-support`s `prepareStackTrace` around to use
  // later, but our cheaper `prepareStackTrace` should be the default.
  prepareStackTraceWithSourceMap = AnyError.prepareStackTrace;
  AnyError.prepareStackTrace = prepareStackTrace;
}

/**
 * Make a copy of the error with a source-mapped stack trace. If it couldn't
 * perform the source mapping, it'll use the original error stack.
 */
export function withSourceMappedStack(error: Error): Error {
  return {
    name: error.name,
    message: error.message,
    stack: sourceMappedStackTrace(error),
  };
}

/** Get the source mapped stack trace for the error. */
function sourceMappedStackTrace(error: Error): string | undefined {
  let frames = stackFrameMap.get(error);

  if (!frames) {
    // At this point there's no guarantee that anyone has actually retrieved the
    // stack on this error which means that our custom prepareStackTrace handler
    // hasn't run and as a result of that we don't have the native frames stored
    // in our weak map. In order to get around that we'll eagerly access the
    // stack, forcing our handler to run which should ensure that the native
    // frames are stored in our weak map.
    (error.stack || '').toString();
    frames = stackFrameMap.get(error);
  }

  if (!frames) {
    return error.stack;
  }

  return prepareStackTraceWithSourceMap(error, frames);
}