Manually fix 'inline' sourcemaps so they work with Webpack.

src/index.js

@@ -115,6 +115,16 @@ async function loader(source, inputSourceMap, overrides) {
       });
     }
 
+    if (options.sourceMaps === "inline") {
+      // Babel has this weird behavior where if you set "inline", we
+      // inline the sourcemap, and set 'result.map = null'. This results
+      // in bad behavior from Babel since the maps get put into the code,
+      // which Webpack does not expect, and because the map we return to
+      // Webpack is null, which is also bad. To avoid that, we override the
+      // behavior here so "inline" just behaves like 'true'.
+      options.sourceMaps = true;
+    }
+
     const {
       cacheDirectory = null,
       cacheIdentifier = JSON.stringify({

test/sourcemaps.test.js

@@ -73,6 +73,53 @@ test.cb("should output webpack's sourcemap", t => {
   });
 });
 
+test.cb("should output webpack's sourcemap properly when set 'inline'", t => {
+  const config = Object.assign({}, globalConfig, {
+    devtool: "source-map",
+    output: {
+      path: t.context.directory,
+    },
+    module: {
+      rules: [
+        {
+          test: /\.jsx?/,
+          loader: babelLoader + "?presets[]=@babel/env&sourceMap=inline",
+          exclude: /node_modules/,
+        },
+      ],
+    },
+  });
+
+  webpack(config, (err, stats) => {
+    t.is(err, null);
+    t.is(stats.compilation.errors.length, 0);
+    t.is(stats.compilation.warnings.length, 0);
+
+    fs.readdir(t.context.directory, (err, files) => {
+      t.is(err, null);
+
+      const map = files.filter(file => file.indexOf(".map") !== -1);
+
+      t.true(map.length > 0);
+
+      if (map.length > 0) {
+        fs.readFile(path.resolve(t.context.directory, map[0]), (err, data) => {
+          t.is(err, null);
+
+          const mapObj = JSON.parse(data.toString());
+
+          t.is(mapObj.sources[1], "webpack:///./test/fixtures/basic.js");
+
+          // Ensure that the map contains the original code, not the
+          // compiled src.
+          t.is(mapObj.sourcesContent[1].indexOf("__esModule"), -1);
+          t.end();
+        });
+      }
+    });
+  });
+});
+
 test.cb("should output webpack's devtoolModuleFilename option", t => {
   const config = Object.assign({}, globalConfig, {
     devtool: "source-map",