module: fix crash on multiline named cjs imports

The node process crashes when trying to parse a multiline import statement for named exports of a CommonJS module: TypeError: Cannot read property '0' of null at ModuleJob._instantiate (internal/modules/esm/module_job.js:112:77) at async ModuleJob.run (internal/modules/esm/module_job.js:137:5) at async Loader.import (internal/modules/esm/loader.js:165:24) at async rejects.name (file:///***/node/test/es-module/test-esm-cjs-named-error.mjs:56:3) at async waitForActual (assert.js:721:5) at async rejects (assert.js:830:25), The reason is that the regexp that is currently used to decorate the original error fails for multi line import statements. Unfortunately the undecorated error stack only contains the single line which causes the import to fail: file:///***/node/test/fixtures/es-modules/package-cjs-named-error/multi-line.mjs:2 comeOn, ^^^^^^ SyntaxError: The requested module './fail.cjs' does not provide an export named 'comeOn' at ModuleJob._instantiate (internal/modules/esm/module_job.js:98:21) at async ModuleJob.run (internal/modules/esm/module_job.js:141:5) at async Loader.import (internal/modules/esm/loader.js:165:24) at async rejects.name (file:///***/node/test/es-module/test-esm-cjs-named-error.mjs:56:3) at async waitForActual (assert.js:721:5) at async rejects (assert.js:830:25) Hence, for multiline import statements we cannot create an equivalent piece of code that uses default import followed by an object destructuring assignment. In any case the node process should definitely not crash. So until we have a more sophisticated way of extracting the entire problematic multiline import statement, show the code example only for single-line imports where the current regexp approach works well. Refs: #35259
nodejs · ctavan · Sep 18, 2020 · Sep 20, 2020 · Sep 20, 2020 · Sep 20, 2020
commit 629827791bb871bd339a3e427f8de8d00ecb8f95
diff --git a/lib/internal/modules/esm/module_job.js b/lib/internal/modules/esm/module_job.js
@@ -108,16 +108,23 @@ class ModuleJob {
               await this.loader.resolve(childSpecifier, parentFileUrl);
         const format = await this.loader.getFormat(childFileURL);
         if (format === 'commonjs') {
-          const importStatement = splitStack[1];
-          const namedImports = StringPrototypeMatch(importStatement, /{.*}/)[0];
-          const destructuringAssignment = StringPrototypeReplace(namedImports, /\s+as\s+/g, ': ');
           e.message = `The requested module '${childSpecifier}' is expected ` +
             'to be of type CommonJS, which does not support named exports. ' +
             'CommonJS modules can be imported by importing the default ' +
-            'export.\n' +
-            'For example:\n' +
-            `import pkg from '${childSpecifier}';\n` +
-            `const ${destructuringAssignment} = pkg;`;
+            'export.';
+          // TODO(@ctavan): The original error stack only provides the single
+          // line which causes the error. For multi-line import statements we
+          // cannot generate an equivalent object descructuring assignment by
+          // just parsing the error stack.
+          const importStatement = splitStack[1];
+          const oneLineNamedImports = StringPrototypeMatch(importStatement, /{.*}/);
+          if (oneLineNamedImports) {
+            const destructuringAssignment =
+              StringPrototypeReplace(oneLineNamedImports[0], /\s+as\s+/g, ': ');
+            e.message += '\nFor example:\n' +
+              `import pkg from '${childSpecifier}';\n` +
+              `const ${destructuringAssignment} = pkg;`;
+          }
           const newStack = StringPrototypeSplit(e.stack, '\n');
           newStack[3] = `SyntaxError: ${e.message}`;
           e.stack = ArrayPrototypeJoin(newStack, '\n');

diff --git a/test/es-module/test-esm-cjs-named-error.mjs b/test/es-module/test-esm-cjs-named-error.mjs
@@ -10,6 +10,10 @@ const expectedRelative = 'The requested module \'./fail.cjs\' is expected to ' +
   'import pkg from \'./fail.cjs\';\n' +
   'const { comeOn } = pkg;';
 
+const expectedWithoutExample = 'The requested module \'./fail.cjs\' is ' +
+  'expected to be of type CommonJS, which does not support named exports. ' +
+  'CommonJS modules can be imported by importing the default export.';
+
 const expectedRenamed = 'The requested module \'./fail.cjs\' is expected to ' +
   'be of type CommonJS, which does not support named exports. CommonJS ' +
   'modules can be imported by importing the default export.\n' +
@@ -52,6 +56,13 @@ rejects(async () => {
   message: expectedRenamed
 }, 'should correctly format named imports with renames');
 
+rejects(async () => {
+  await import(`${fixtureBase}/multi-line.mjs`);
+}, {
+  name: 'SyntaxError',
+  message: expectedWithoutExample,
+}, 'should correctly format named imports across multiple lines');
+
 rejects(async () => {
   await import(`${fixtureBase}/json-hack.mjs`);
 }, {

diff --git a/test/fixtures/es-modules/package-cjs-named-error/fail.cjs b/test/fixtures/es-modules/package-cjs-named-error/fail.cjs
@@ -1,3 +1,4 @@
 module.exports = {
-  comeOn: 'fhqwhgads'
+  comeOn: 'fhqwhgads',
+  rightNow: 'abcde',
 };
diff --git a/test/fixtures/es-modules/package-cjs-named-error/multi-line.mjs b/test/fixtures/es-modules/package-cjs-named-error/multi-line.mjs
@@ -0,0 +1,4 @@
+import {
+  comeOn,
+  rightNow,
+} from './fail.cjs';