From 8f38c19c0860daa13563f4c9ab253cd9b5be49ab Mon Sep 17 00:00:00 2001
From: Denys Otrishko <shishugi@gmail.com>
Date: Sun, 16 Aug 2020 12:28:54 +0300
Subject: [PATCH] esm: improve error message of ERR_UNSUPPORTED_ESM_URL_SCHEME

Refs: https://github.com/nodejs/node/issues/34765

PR-URL: https://github.com/nodejs/node/pull/34795
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Bradley Farias <bradley.meck@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 lib/internal/errors.js                    | 13 +++++++++++--
 lib/internal/modules/esm/resolve.js       |  2 +-
 test/es-module/test-esm-dynamic-import.js | 23 ++++++++++++++---------
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 54a05df736148f..191d51552f7d22 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -26,6 +26,8 @@ const {
   WeakMap,
 } = primordials;
 
+const isWindows = process.platform === 'win32';
+
 const messages = new Map();
 const codes = {};
 
@@ -1410,8 +1412,15 @@ E('ERR_UNKNOWN_MODULE_FORMAT', 'Unknown module format: %s', RangeError);
 E('ERR_UNKNOWN_SIGNAL', 'Unknown signal: %s', TypeError);
 E('ERR_UNSUPPORTED_DIR_IMPORT', "Directory import '%s' is not supported " +
 'resolving ES modules imported from %s', Error);
-E('ERR_UNSUPPORTED_ESM_URL_SCHEME', 'Only file and data URLs are supported ' +
-  'by the default ESM loader', Error);
+E('ERR_UNSUPPORTED_ESM_URL_SCHEME', (url) => {
+  let msg = 'Only file and data URLs are supported by the default ESM loader';
+  if (isWindows && url.protocol.length === 2) {
+    msg += '. Absolute Windows paths without prefix are not valid URLs, ' +
+      "consider using 'file://' prefix";
+  }
+  msg += `. Received protocol '${url.protocol}'`;
+  return msg;
+}, Error);
 
 // This should probably be a `TypeError`.
 E('ERR_VALID_PERFORMANCE_ENTRY_TYPE',
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index 04a17c908ad91b..d58eac5f1c10cb 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -747,7 +747,7 @@ function defaultResolve(specifier, context = {}, defaultResolveUnused) {
   if (parsed && parsed.protocol === 'nodejs:')
     return { url: specifier };
   if (parsed && parsed.protocol !== 'file:' && parsed.protocol !== 'data:')
-    throw new ERR_UNSUPPORTED_ESM_URL_SCHEME();
+    throw new ERR_UNSUPPORTED_ESM_URL_SCHEME(parsed);
   if (NativeModule.canBeRequiredByUsers(specifier)) {
     return {
       url: 'nodejs:' + specifier
diff --git a/test/es-module/test-esm-dynamic-import.js b/test/es-module/test-esm-dynamic-import.js
index e72922d31c0b18..30a5758ad9b0d4 100644
--- a/test/es-module/test-esm-dynamic-import.js
+++ b/test/es-module/test-esm-dynamic-import.js
@@ -8,15 +8,11 @@ const absolutePath = require.resolve('../fixtures/es-modules/test-esm-ok.mjs');
 const targetURL = new URL('file:///');
 targetURL.pathname = absolutePath;
 
-function expectErrorProperty(result, propertyKey, value) {
-  Promise.resolve(result)
-    .catch(common.mustCall((error) => {
-      assert.strictEqual(error[propertyKey], value);
-    }));
-}
-
-function expectModuleError(result, err) {
-  expectErrorProperty(result, 'code', err);
+function expectModuleError(result, code, message) {
+  Promise.resolve(result).catch(common.mustCall((error) => {
+    assert.strictEqual(error.code, code);
+    if (message) assert.strictEqual(error.message, message);
+  }));
 }
 
 function expectOkNamespace(result) {
@@ -60,4 +56,13 @@ function expectFsNamespace(result) {
                     'ERR_MODULE_NOT_FOUND');
   expectModuleError(import('http://example.com/foo.js'),
                     'ERR_UNSUPPORTED_ESM_URL_SCHEME');
+  if (common.isWindows) {
+    const msg =
+      'Only file and data URLs are supported by the default ESM loader. ' +
+      'Absolute Windows paths without prefix are not valid URLs, ' +
+      "consider using 'file://' prefix. Received protocol 'c:'";
+    expectModuleError(import('C:\\example\\foo.mjs'),
+                      'ERR_UNSUPPORTED_ESM_URL_SCHEME',
+                      msg);
+  }
 })();