metro-minify-terser: Don't mutate input options

Summary:
Mitigates terser/terser#1341

Terser sets properties inlcuding `source_map` and `_destroy_ast` on the given `options.output` (or `options.format`) object, which can affect subsequent calls where we re-use the same config object.

Here we take a shallow copy of the given configuration, so `terser` doesn't mutate `metro-minify-terser`'s input.

Changelog: [Fix] Mitigate potential source map mismatches with concurrent transformations (Terser [facebook#1341](terser/terser#1341))

Reviewed By: jacdebug, motiz88

Differential Revision: D43362977

fbshipit-source-id: 019f417aa8cc7897c71a6ab2c7db5d0cf916e59d

packages/metro-minify-terser/src/__tests__/terser-issue-1341-test.js

@@ -0,0 +1,92 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+import minify from '../minifier';
+
+const config = {
+  mangle: {
+    toplevel: false,
+  },
+  output: {
+    ascii_only: true,
+    quote_style: 3,
+    wrap_iife: true,
+  },
+  sourceMap: {
+    includeSources: false,
+  },
+  toplevel: false,
+  compress: {
+    reduce_funcs: false,
+  },
+};
+
+const BAR = {
+  filename: '',
+  code: '__d(function(global,_$$_REQUIRE,_$$_IMPORT_DEFAULT,_$$_IMPORT_ALL,module,exports,_$$_METRO_DEPENDENCY_MAP){"use strict";function bar(){return new Promise(function(resolve){return resolve(_$$_REQUIRE(_$$_METRO_DEPENDENCY_MAP[0]));}).then(function onGlo(glo){makeItThrow(glo);});}function makeItThrow(glo){makeItThrowInner(glo);}function makeItThrowInner(glo){glo.throwSmth();}module.exports=bar;});',
+  map: {
+    version: 3,
+    sources: ['js/RKJSModules/bar.js'],
+    sourcesContent: [
+      "'use strict';\n\nfunction bar() {\n  return new Promise(resolve => resolve(require('./segmented/glo.js'))).then(function onGlo(glo) {\n    makeItThrow(glo);\n  });\n}\n\nfunction makeItThrow(glo) {\n  makeItThrowInner(glo);\n}\n\nfunction makeItThrowInner(glo) {\n  glo.throwSmth();\n}\n\nmodule.exports = bar;\n",
+    ],
+    names: [
+      'bar',
+      'Promise',
+      'resolve',
+      'require',
+      'then',
+      'onGlo',
+      'glo',
+      'makeItThrow',
+      'makeItThrowInner',
+      'throwSmth',
+      'module',
+      'exports',
+    ],
+    mappings:
+      '2GAAA,YAAY,CAEZ,QAASA,IAAG,EAAG,CACb,MAAO,IAAIC,QAAO,CAAC,SAAAC,OAAO,QAAIA,QAAO,CAACC,WAAO,6BAAsB,CAAC,GAAC,CAACC,IAAI,CAAC,QAASC,MAAK,CAACC,GAAG,CAAE,CAC7FC,WAAW,CAACD,GAAG,CAAC,CAClB,CAAC,CAAC,CACJ,CAEA,QAASC,YAAW,CAACD,GAAG,CAAE,CACxBE,gBAAgB,CAACF,GAAG,CAAC,CACvB,CAEA,QAASE,iBAAgB,CAACF,GAAG,CAAE,CAC7BA,GAAG,CAACG,SAAS,EAAE,CACjB,CAEAC,MAAM,CAACC,OAAO,CAAGX,GAAG,CAAC',
+  },
+  reserved: ['_$$_METRO_DEPENDENCY_MAP'],
+  config,
+};
+
+const GLO = {
+  filename: '',
+  code: '__d(function(global,_$$_REQUIRE,_$$_IMPORT_DEFAULT,_$$_IMPORT_ALL,module,exports,_$$_METRO_DEPENDENCY_MAP){"use strict";var biz=_$$_REQUIRE(_$$_METRO_DEPENDENCY_MAP[0]);module.exports={throwSmth:function throwSmth(){return biz.throwSmthInner();}};});',
+  map: {
+    version: 3,
+    sources: ['js/RKJSModules/segmented/glo.js'],
+    sourcesContent: [
+      "'use strict';\n\nconst biz = require('./biz');\n\nmodule.exports = {\n  throwSmth() {\n    return biz.throwSmthInner();\n  },\n};",
+    ],
+    names: [
+      'biz',
+      'require',
+      'module',
+      'exports',
+      'throwSmth',
+      'throwSmthInner',
+    ],
+    mappings:
+      '2GAAA,YAAY,CAEZ,GAAMA,IAAG,CAAGC,WAAO,6BAAS,CAE5BC,MAAM,CAACC,OAAO,CAAG,CACfC,SAAS,qBAAG,CACV,MAAOJ,IAAG,CAACK,cAAc,EAAE,CAC7B,CACF,CAAC,CAAC',
+  },
+  reserved: ['_$$_METRO_DEPENDENCY_MAP'],
+  config,
+};
+
+test('parallel calls do not clobber each other', async () => {
+  const [barResult, gloResult] = await Promise.all([minify(BAR), minify(GLO)]);
+
+  const barMap = barResult.map;
+  const gloMap = gloResult.map;
+
+  expect(gloMap).not.toEqual(barMap);
+});

packages/metro-minify-terser/src/minifier.js

@@ -36,6 +36,11 @@ async function minify({
 }: MinifierOptions): Promise<{code: string, map: ?string}> {
   const options = {
     ...config,
+    output: {
+      // Mitigate https://github.com/terser/terser/issues/1341 - Terser may
+      // set its internal data on this object, so give it a shallow copy.
+      ...(config.output ?? {}),
+    },
     mangle:
       config.mangle === false
         ? false