Updated the files.

my-app/node_modules/resolve-url-loader/lib/join-function/debug.js

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+/*
+ * MIT License http://opensource.org/licenses/MIT
+ * Author: Ben Holloway @bholloway
+ */
+'use strict';
+
+const path = require('path');
+
+const PACKAGE_NAME = require('../../package.json').name;
+
+/**
+ * Paths are formatted to have posix style path separators and those within the CWD are made relative to CWD.
+ *
+ * @param {string} absolutePath An absolute path to format
+ * @returns {string} the formatted path
+ */
+const pathToString = (absolutePath) => {
+  if (absolutePath === '') {
+    return '-empty-';
+  } else {
+    const relative = path.relative(process.cwd(), absolutePath).split(path.sep);
+    const segments =
+      (relative[0] !== '..') ? ['.'].concat(relative).filter(Boolean) :
+        (relative.lastIndexOf('..') < 2) ? relative :
+          absolutePath.replace(/^[A-Z]\:/, '').split(path.sep);
+    return segments.join('/');
+  }
+};
+
+exports.pathToString = pathToString;
+
+/**
+ * Format a debug message.
+ *
+ * @param {string} filename The file being processed by webpack
+ * @param {string} uri A uri path, relative or absolute
+ * @param {Array<{base:string,joined:string,isSuccess:boolean}>} attempts An array of attempts, possibly empty
+ * @return {string} Formatted message
+ */
+const formatJoinMessage = (filename, uri, attempts) => {
+  const attemptToCells = (_, i, array) => {
+    const { base: prev } = (i === 0) ? {} : array[i-1];
+    const { base: curr, joined } = array[i];
+    return [(curr === prev) ? '' : pathToString(curr), pathToString(joined)];
+  };
+
+  const formatCells = (lines) => {
+    const maxWidth = lines.reduce((max, [cellA]) => Math.max(max, cellA.length), 0);
+    return lines.map(([cellA, cellB]) => [cellA.padEnd(maxWidth), cellB]).map((cells) => cells.join(' --> '));
+  };
+
+  return [PACKAGE_NAME + ': ' + pathToString(filename) + ': ' + uri]
+    .concat(attempts.length === 0 ? '-empty-' : formatCells(attempts.map(attemptToCells)))
+    .concat(attempts.some(({ isSuccess }) => isSuccess) ? 'FOUND' : 'NOT FOUND')
+    .join('\n  ');
+};
+
+exports.formatJoinMessage = formatJoinMessage;
+
+/**
+ * A factory for a log function predicated on the given debug parameter.
+ *
+ * The logging function created accepts a function that formats a message and parameters that the function utilises.
+ * Presuming the message function may be expensive we only call it if logging is enabled.
+ *
+ * The log messages are de-duplicated based on the parameters, so it is assumed they are simple types that stringify
+ * well.
+ *
+ * @param {function|boolean} debug A boolean or debug function
+ * @return {function(function, array):void} A logging function possibly degenerate
+ */
+const createDebugLogger = (debug) => {
+  const log = !!debug && ((typeof debug === 'function') ? debug : console.log);
+  const cache = {};
+  return log ?
+    ((msgFn, params) => {
+      const key = Function.prototype.toString.call(msgFn) + JSON.stringify(params);
+      if (!cache[key]) {
+        cache[key] = true;
+        log(msgFn.apply(null, params));
+      }
+    }) :
+    (() => undefined);
+};
+
+exports.createDebugLogger = createDebugLogger;

my-app/node_modules/resolve-url-loader/lib/join-function/fs-utils.js

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+/*
+ * MIT License http://opensource.org/licenses/MIT
+ * Author: Ben Holloway @bholloway
+ */
+'use strict';
+
+const fsUtils = (fs) => {
+  // fs from enhanced-resolver doesn't include fs.existsSync so we need to use fs.statsSync instead
+  const withStats = (fn) => (absolutePath) => {
+    try {
+      return fn(fs.statSync(absolutePath));
+    } catch (e) {
+      return false;
+    }
+  };
+
+  return {
+    isFileSync: withStats((stats) => stats.isFile()),
+    isDirectorySync: withStats((stats) => stats.isDirectory()),
+    existsSync: withStats((stats) => stats.isFile() || stats.isDirectory())
+  };
+};
+
+module.exports = fsUtils;

my-app/node_modules/resolve-url-loader/lib/join-function/index.js

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+/*
+ * MIT License http://opensource.org/licenses/MIT
+ * Author: Ben Holloway @bholloway
+ */
+'use strict';
+
+const path = require('path');
+
+const { createDebugLogger, formatJoinMessage } = require('./debug');
+const fsUtils = require('./fs-utils');
+
+const ITERATION_SAFETY_LIMIT = 100e3;
+
+/**
+ * Wrap a function such that it always returns a generator of tuple elements.
+ *
+ * @param {function({uri:string},...):(Array|Iterator)<[string,string]|string>} fn The function to wrap
+ * @returns {function({uri:string},...):(Array|Iterator)<[string,string]>} A function that always returns tuple elements
+ */
+const asGenerator = (fn) => {
+  const toTuple = (defaults) => (value) => {
+    const partial = [].concat(value);
+    return [...partial, ...defaults.slice(partial.length)];
+  };
+
+  const isTupleUnique = (v, i, a) => {
+    const required = v.join(',');
+    return a.findIndex((vv) => vv.join(',') === required) === i;
+  };
+
+  return (item, ...rest) => {
+    const {uri} = item;
+    const mapTuple = toTuple([null, uri]);
+    const pending = fn(item, ...rest);
+    if (Array.isArray(pending)) {
+      return pending.map(mapTuple).filter(isTupleUnique)[Symbol.iterator]();
+    } else if (
+      pending &&
+      (typeof pending === 'object') &&
+      (typeof pending.next === 'function') &&
+      (pending.next.length === 0)
+    ) {
+      return pending;
+    } else {
+      throw new TypeError(`in "join" function expected "generator" to return Array|Iterator`);
+    }
+  };
+};
+
+exports.asGenerator = asGenerator;
+
+/**
+ * A high-level utility to create a join function.
+ *
+ * The `generator` is responsible for ordering possible base paths. The `operation` is responsible for joining a single
+ * `base` path with the given `uri`. The `predicate` is responsible for reporting whether the single joined value is
+ * successful as the overall result.
+ *
+ * Both the `generator` and `operation` may be `function*()` or simply `function(...):Array<string>`.
+ *
+ * @param {function({uri:string, isAbsolute:boolean, bases:{subString:string, value:string, property:string,
+ *  selector:string}}, {filename:string, fs:Object, debug:function|boolean, root:string}):
+ *  (Array<string>|Iterator<string>)} generator A function that takes the hash of base paths from the `engine` and
+ *  returns ordered iterable of paths to consider
+ * @returns {function({filename:string, fs:Object, debug:function|boolean, root:string}):
+ *  (function({uri:string, isAbsolute:boolean, bases:{subString:string, value:string, property:string,
+ *  selector:string}}):string)} join implementation
+ */
+const createJoinImplementation = (generator) => (item, options, loader) => {
+  const { isAbsolute } = item;
+  const { root } = options;
+  const { fs } = loader;
+
+  // generate the iterator
+  const iterator = generator(item, options, loader);
+  const isValidIterator = iterator && typeof iterator === 'object' && typeof iterator.next === 'function';
+  if (!isValidIterator) {
+    throw new Error('expected generator to return Iterator');
+  }
+
+  // run the iterator lazily and record attempts
+  const { isFileSync, isDirectorySync } = fsUtils(fs);
+  const attempts = [];
+  for (let i = 0; i < ITERATION_SAFETY_LIMIT; i++) {
+    const { value, done } = iterator.next();
+    if (done) {
+      break;
+    } else if (value) {
+      const tuple = Array.isArray(value) && value.length === 2 ? value : null;
+      if (!tuple) {
+        throw new Error('expected Iterator values to be tuple of [string,string], do you need asGenerator utility?');
+      }
+
+      // skip elements where base or uri is non-string
+      // noting that we need to support base="" when root=""
+      const [base, uri] = value;
+      if ((typeof base === 'string') && (typeof uri === 'string')) {
+
+        // validate
+        const isValidBase = (isAbsolute && base === root) || (path.isAbsolute(base) && isDirectorySync(base));
+        if (!isValidBase) {
+          throw new Error(`expected "base" to be absolute path to a valid directory, got "${base}"`);
+        }
+
+        // make the attempt
+        const joined = path.normalize(path.join(base, uri));
+        const isFallback = true;
+        const isSuccess = isFileSync(joined);
+        attempts.push({base, uri, joined, isFallback, isSuccess});
+
+        if (isSuccess) {
+          break;
+        }
+
+      // validate any non-strings are falsey
+      } else {
+        const isValidTuple = value.every((v) => (typeof v === 'string') || !v);
+        if (!isValidTuple) {
+          throw new Error('expected Iterator values to be tuple of [string,string]');
+        }
+      }
+    }
+  }
+
+  return attempts;
+};
+
+exports.createJoinImplementation = createJoinImplementation;
+
+/**
+ * A low-level utility to create a join function.
+ *
+ * The `implementation` function processes an individual `item` and returns an Array of attempts. Each attempt consists
+ * of a `base` and a `joined` value with `isSuccessful` and `isFallback` flags.
+ *
+ * In the case that any attempt `isSuccessful` then its `joined` value is the outcome. Otherwise the first `isFallback`
+ * attempt is used. If there is no successful or fallback attempts then `null` is returned indicating no change to the
+ * original URI in the CSS.
+ *
+ * The `attempts` Array is logged to console when in `debug` mode.
+ *
+ * @param {string} name Name for the resulting join function
+ * @param {function({uri:string, query:string, isAbsolute:boolean, bases:{subString:string, value:string,
+ *  property:string, selector:string}}, {filename:string, fs:Object, debug:function|boolean, root:string}):
+ *  Array<{base:string,joined:string,fallback?:string,result?:string}>} implementation A function accepts an item and
+ *  returns a list of attempts
+ * @returns {function({filename:string, fs:Object, debug:function|boolean, root:string}):
+ *  (function({uri:string, isAbsolute:boolean, bases:{subString:string, value:string, property:string,
+ *  selector:string}}):string)} join function
+ */
+const createJoinFunction = (name, implementation) => {
+  const assertAttempts = (value) => {
+    const isValid =
+      Array.isArray(value) && value.every((v) =>
+        v &&
+        (typeof v === 'object') &&
+        (typeof v.base === 'string') &&
+        (typeof v.uri === 'string') &&
+        (typeof v.joined === 'string') &&
+        (typeof v.isSuccess === 'boolean') &&
+        (typeof v.isFallback === 'boolean')
+      );
+    if (!isValid) {
+      throw new Error(`expected implementation to return Array of {base, uri, joined, isSuccess, isFallback}`);
+    } else {
+      return value;
+    }
+  };
+
+  const assertJoined = (value) => {
+    const isValid = value && (typeof value === 'string') && path.isAbsolute(value) || (value === null);
+    if (!isValid) {
+      throw new Error(`expected "joined" to be absolute path, got "${value}"`);
+    } else {
+      return value;
+    }
+  };
+
+  const join = (options, loader) => {
+    const { debug } = options;
+    const { resourcePath } = loader;
+    const log = createDebugLogger(debug);
+
+    return (item) => {
+      const { uri } = item;
+      const attempts = implementation(item, options, loader);
+      assertAttempts(attempts, !!debug);
+
+      const { joined: fallback } = attempts.find(({ isFallback }) => isFallback) || {};
+      const { joined: result } = attempts.find(({ isSuccess }) => isSuccess) || {};
+
+      log(formatJoinMessage, [resourcePath, uri, attempts]);
+
+      return assertJoined(result || fallback || null);
+    };
+  };
+
+  const toString = () => '[Function ' + name + ']';
+
+  return Object.assign(join, !!name && {
+    toString,
+    toJSON: toString
+  });
+};
+
+exports.createJoinFunction = createJoinFunction;
+
+/**
+ * The default iterable factory will order `subString` then `value` then `property` then `selector`.
+ *
+ * @param {string} uri The uri given in the file webpack is processing
+ * @param {boolean} isAbsolute True for absolute URIs, false for relative URIs
+ * @param {string} subString A possible base path
+ * @param {string} value A possible base path
+ * @param {string} property A possible base path
+ * @param {string} selector A possible base path
+ * @param {string} root The loader options.root value where given
+ * @returns {Array<string>} An iterable of possible base paths in preference order
+ */
+const defaultJoinGenerator = asGenerator(
+  ({ uri, isAbsolute, bases: { subString, value, property, selector } }, { root }) =>
+    isAbsolute ? [root] : [subString, value, property, selector]
+);
+
+exports.defaultJoinGenerator = defaultJoinGenerator;
+
+/**
+ * @type {function({filename:string, fs:Object, debug:function|boolean, root:string}):
+ *  (function({uri:string, isAbsolute:boolean, bases:{subString:string, value:string, property:string,
+ *  selector:string}}):string)} join function
+ */
+exports.defaultJoin = createJoinFunction(
+  'defaultJoin',
+  createJoinImplementation(defaultJoinGenerator)
+);