fix(commonjs): initialize replaced module.exports to {} for circular requires

packages/commonjs/src/generate-exports.js

@@ -35,7 +35,8 @@ export function rewriteExportsAndGetExportsBlock(
   exportMode,
   defaultIsModuleExports,
   usesRequireWrapper,
-  requireName
+  requireName,
+  usesTopLevelThis
 ) {
   const exports = [];
   const exportDeclarations = [];
@@ -62,7 +63,8 @@ export function rewriteExportsAndGetExportsBlock(
       firstTopLevelModuleExportsAssignment,
       exportsName,
       defaultIsModuleExports,
-      HELPERS_NAME
+      HELPERS_NAME,
+      usesTopLevelThis
     );
   } else {
     if (exportMode === 'module') {
@@ -149,12 +151,19 @@ function getExportsForReplacedModuleExports(
   firstTopLevelModuleExportsAssignment,
   exportsName,
   defaultIsModuleExports,
-  HELPERS_NAME
+  HELPERS_NAME,
+  usesTopLevelThis
 ) {
   for (const { left } of moduleExportsAssignments) {
     magicString.overwrite(left.start, left.end, exportsName);
   }
-  magicString.prependRight(firstTopLevelModuleExportsAssignment.left.start, 'var ');
+  if (usesTopLevelThis) {
+    // Top-level `this` is rewritten to exportsName and may run before the
+    // assignment, so the variable must already hold Node's initial `{}`.
+    magicString.prepend(`var ${exportsName} = {};\n`);
+  } else {
+    magicString.prependRight(firstTopLevelModuleExportsAssignment.left.start, 'var ');
+  }
   exports.push(`${exportsName} as __moduleExports`);
   exportDeclarations.push(
     getDefaultExportDeclaration(exportsName, defaultIsModuleExports, HELPERS_NAME)

packages/commonjs/src/transform-commonjs.js

@@ -556,7 +556,8 @@ export default async function transformCommonjs(
         exportMode,
         defaultIsModuleExports,
         usesRequireWrapper,
-        requireName
+        requireName,
+        replacedThis.length > 0
       );
 
   if (shouldWrap) {
@@ -568,13 +569,18 @@ export default async function transformCommonjs(
       exclude: indentExclusionRanges
     });
     const exported = exportMode === 'module' ? `${moduleName}.exports` : exportsName;
+    // A replaced module.exports starts from an empty object like it does in Node,
+    // so that a circular require or a top-level `this` before the
+    // `module.exports =` assignment sees `{}`. It is set when the first require
+    // starts, so a value that a re-entrant require already completed is kept.
+    const initialExports = exportMode === 'replace' ? `\t${exportsName} = {};\n` : '';
     magicString.prepend(
       `var ${isRequiredName};
 
 function ${requireName} () {
 \tif (${isRequiredName}) return ${exported};
 \t${isRequiredName} = 1;
-`
+${initialExports}`
     ).append(`
 \treturn ${exported};
 }`);

packages/commonjs/test/fixtures/form/async-function/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = async function () {
 		// TODO
 	};

packages/commonjs/test/fixtures/form/defaultIsModuleExports-auto-reassign-exports-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { __esModule: true, default: { foo: 'bar' }}
 	return input;
 }

packages/commonjs/test/fixtures/form/defaultIsModuleExports-auto-reassign-exports-no-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { default: { foo: 'bar' }}
 	return input;
 }

packages/commonjs/test/fixtures/form/defaultIsModuleExports-false-reassign-exports-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { __esModule: true, default: { foo: 'bar' }};
 	return input;
 }

packages/commonjs/test/fixtures/form/defaultIsModuleExports-false-reassign-exports-no-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { default: { foo: 'bar' }};
 	return input;
 }

packages/commonjs/test/fixtures/form/defaultIsModuleExports-true-reassign-exports-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { __esModule: true, default: { foo: 'bar' }};
 	return input;
 }

packages/commonjs/test/fixtures/form/defaultIsModuleExports-true-reassign-exports-no-__esModule/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = { default: { foo: 'bar' }};
 	return input;
 }

packages/commonjs/test/fixtures/form/multi-entry-module-exports/output1.js

@@ -7,6 +7,7 @@ var hasRequiredInput1;
 function requireInput1 () {
 	if (hasRequiredInput1) return input1;
 	hasRequiredInput1 = 1;
+	input1 = {};
 	const t2 = require$$0;
 
 	console.log(t2);

packages/commonjs/test/fixtures/form/multi-entry-module-exports/output2.js

@@ -6,6 +6,7 @@ var hasRequiredInput2;
 function requireInput2 () {
 	if (hasRequiredInput2) return input2;
 	hasRequiredInput2 = 1;
+	input2 = {};
 	input2 = {
 	  a: 2
 	};

packages/commonjs/test/fixtures/form/no-toplevel-return/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	var foo = function () {
 		return;
 	};

packages/commonjs/test/fixtures/form/optimised-default-export-function-double-assign/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	var bar;
 	input = bar = function foo () {};
 	return input;

packages/commonjs/test/fixtures/form/optimised-default-export-function/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = function foo () {};
 	return input;
 }

packages/commonjs/test/fixtures/form/optimised-default-export-iife/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = (function foo () {
 	  return function fooChild() {};
 	}());

packages/commonjs/test/fixtures/form/optimised-default-export/output.js

@@ -6,6 +6,7 @@ var hasRequiredInput;
 function requireInput () {
 	if (hasRequiredInput) return input;
 	hasRequiredInput = 1;
+	input = {};
 	input = 42;
 	return input;
 }

packages/commonjs/test/fixtures/function/strict-requires-circular-replace-mixed/_config.js

@@ -0,0 +1,14 @@
+module.exports = {
+  description:
+    'keeps a replaced module.exports that a re-entrant require completed through an ES module',
+  options: {
+    onwarn(warning) {
+      if (warning.code !== 'CIRCULAR_DEPENDENCY') {
+        throw new Error(warning.message);
+      }
+    }
+  },
+  pluginOptions: {
+    strictRequires: true
+  }
+};

packages/commonjs/test/fixtures/function/strict-requires-circular-replace-mixed/a.js

@@ -0,0 +1,3 @@
+require('./b.js');
+
+module.exports = 42;

packages/commonjs/test/fixtures/function/strict-requires-circular-replace-mixed/b.js

@@ -0,0 +1,3 @@
+import c from './c.js';
+
+export default c;

packages/commonjs/test/fixtures/function/strict-requires-circular-replace-mixed/c.js

@@ -0,0 +1 @@
+module.exports = require('./a.js');

packages/commonjs/test/fixtures/function/strict-requires-circular-replace-mixed/main.js

@@ -0,0 +1,2 @@
+t.is(require('./a.js'), 42);
+t.is(require('./a.js'), 42);

packages/commonjs/test/fixtures/function/strict-requires-circular-replace/_config.js

@@ -0,0 +1,7 @@
+module.exports = {
+  description:
+    'provides the initial exports object to a circular require before module.exports is replaced',
+  pluginOptions: {
+    strictRequires: true
+  }
+};

packages/commonjs/test/fixtures/function/strict-requires-circular-replace/a.js

@@ -0,0 +1,3 @@
+const b = require('./b.js');
+
+module.exports = { seenByB: b.seen };

packages/commonjs/test/fixtures/function/strict-requires-circular-replace/b.js

@@ -0,0 +1,3 @@
+const a = require('./a.js');
+
+module.exports = { seen: typeof a };

packages/commonjs/test/fixtures/function/strict-requires-circular-replace/main.js

@@ -0,0 +1 @@
+t.deepEqual(require('./a.js'), { seenByB: 'object' });

packages/commonjs/test/fixtures/function/strict-requires-this-before-replace/_config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  description: 'allows top-level this before module.exports is replaced',
+  pluginOptions: {
+    strictRequires: true
+  }
+};

packages/commonjs/test/fixtures/function/strict-requires-this-before-replace/main.js

@@ -0,0 +1 @@
+t.deepEqual(require('./other.js'), { y: 2 });

packages/commonjs/test/fixtures/function/strict-requires-this-before-replace/other.js

@@ -0,0 +1,3 @@
+this.x = 1;
+
+module.exports = { y: 2 };

packages/commonjs/test/fixtures/function/this-before-replace-auto/_config.js

@@ -0,0 +1,7 @@
+module.exports = {
+  description:
+    'allows top-level this before module.exports is replaced when strictRequires is auto',
+  pluginOptions: {
+    strictRequires: 'auto'
+  }
+};

packages/commonjs/test/fixtures/function/this-before-replace-auto/main.js

@@ -0,0 +1 @@
+t.deepEqual(require('./other.js'), { y: 2 });

packages/commonjs/test/fixtures/function/this-before-replace-auto/other.js

@@ -0,0 +1,3 @@
+this.x = 1;
+
+module.exports = { y: 2 };

packages/commonjs/test/fixtures/function/this-before-replace-unwrapped/_config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  description: 'allows top-level this before module.exports is replaced in an unwrapped module',
+  pluginOptions: {
+    strictRequires: false
+  }
+};

packages/commonjs/test/fixtures/function/this-before-replace-unwrapped/main.js

@@ -0,0 +1 @@
+t.deepEqual(require('./other.js'), { y: 2 });

packages/commonjs/test/fixtures/function/this-before-replace-unwrapped/other.js

@@ -0,0 +1,3 @@
+this.x = 1;
+
+module.exports = { y: 2 };