fix: source map consumer could be synchronious

src/webpack/index.js

@@ -2,7 +2,7 @@
 
 const fs = require('fs');
 const path = require('path');
-const { SourceNode, SourceMapConsumer } = require('source-map');
+const {SourceNode, SourceMapConsumer} = require('source-map');
 const loaderUtils = require('loader-utils');
 const makeIdentitySourceMap = require('./makeIdentitySourceMap');
 const patch = require('./patch');
@@ -11,27 +11,28 @@ let tagCommonJSExportsSource = null;
 
 function transform(source, map) {
   const callback = this.async();
+  const resourcePath = this.resourcePath;
 
   if (process.env.NODE_ENV === 'production') {
     return callback(null, source, map);
   }
   if (source && source.types && source.types.IfStatement) {
     throw new Error(
       'React Hot Loader: You are erroneously trying to use a Webpack loader ' +
-        'as a Babel plugin. Replace "react-hot-loader/webpack" with ' +
-        '"react-hot-loader/babel" in the "plugins" section of your .babelrc file. ' +
-        'While we recommend the above, if you prefer not to use Babel, ' +
-        'you may remove "react-hot-loader/webpack" from the "plugins" section of ' +
-        'your .babelrc file altogether, and instead add "react-hot-loader/webpack" ' +
-        'to the "loaders" section of your Webpack configuration.',
+      'as a Babel plugin. Replace "react-hot-loader/webpack" with ' +
+      '"react-hot-loader/babel" in the "plugins" section of your .babelrc file. ' +
+      'While we recommend the above, if you prefer not to use Babel, ' +
+      'you may remove "react-hot-loader/webpack" from the "plugins" section of ' +
+      'your .babelrc file altogether, and instead add "react-hot-loader/webpack" ' +
+      'to the "loaders" section of your Webpack configuration.',
     );
   }
 
   if (this.cacheable) {
     this.cacheable();
   }
 
-  const options = Object.assign({ withPatch: true }, loaderUtils.getOptions(this));
+  const options = Object.assign({withPatch: true}, loaderUtils.getOptions(this));
   if (options.withPatch) {
     source = patch(source);
   }
@@ -56,24 +57,31 @@ function transform(source, map) {
 
   // Parameterize the helper with the current filename.
   const separator = '\n\n;';
-  const appendText = tagCommonJSExportsSource.replace(/__FILENAME__/g, JSON.stringify(this.resourcePath));
+  const appendText = tagCommonJSExportsSource.replace(/__FILENAME__/g, JSON.stringify(resourcePath));
 
   if (this.sourceMap === false) {
     return callback(null, [source, appendText].join(separator));
   }
 
   if (!map) {
-    map = makeIdentitySourceMap(source, this.resourcePath); // eslint-disable-line no-param-reassign
+    map = makeIdentitySourceMap(source, resourcePath); // eslint-disable-line no-param-reassign
   }
   const sourceMapConsumer = new SourceMapConsumer(map);
-  sourceMapConsumer.then(consumedMap => {
+
+  const onSourceMapReady = consumedMap => {
     const node = new SourceNode(null, null, null, [
       SourceNode.fromStringWithSourceMap(source, consumedMap),
-      new SourceNode(null, null, this.resourcePath, appendText),
+      new SourceNode(null, null, resourcePath, appendText),
     ]).join(separator);
     const result = node.toStringWithSourceMap();
     callback(null, result.code, result.map.toJSON() || undefined);
-  });
+  };
+
+  if (sourceMapConsumer.then) {
+    sourceMapConsumer.then(onSourceMapReady);
+  } else {
+    onSourceMapReady(sourceMapConsumer);
+  }
 }
 
 transform.patch = patch;