module: unflag import assertions

Unflag import assertions and remove possibility of importing JSON
modules without using an assertion.

Refs: nodejs#37375 (comment)
Co-authored-by: Geoffrey Booth <webadmin@geoffreybooth.com>

doc/api/errors.md

@@ -1111,6 +1111,14 @@ The JS execution context is not associated with a Node.js environment.
 This may occur when Node.js is used as an embedded library and some hooks
 for the JS engine are not set up properly.
 
+<a id="ERR_FAILED_IMPORT_ASSERTION"></a>
+### `ERR_FAILED_IMPORT_ASSERTION`
+<!-- YAML
+added: REPLACEME
+-->
+
+An import assertion has failed, preventing the specified module to be imported.
+
 <a id="ERR_FALSY_VALUE_REJECTION"></a>
 ### `ERR_FALSY_VALUE_REJECTION`
 
@@ -1662,6 +1670,14 @@ for more information.
 
 An invalid HTTP token was supplied.
 
+<a id="ERR_INVALID_IMPORT_ASSERTION"></a>
+### `ERR_INVALID_IMPORT_ASSERTION`
+<!-- YAML
+added: REPLACEME
+-->
+
+An import assertion is not supported by this version of Node.js.
+
 <a id="ERR_INVALID_IP_ADDRESS"></a>
 ### `ERR_INVALID_IP_ADDRESS`
 
@@ -1913,6 +1929,15 @@ strict compliance with the API specification (which in some cases may accept
 `func(undefined)` and `func()` are treated identically, and the
 [`ERR_INVALID_ARG_TYPE`][] error code may be used instead.
 
+<a id="ERR_MISSING_IMPORT_ASSERTION"></a>
+### `ERR_MISSING_IMPORT_ASSERTION`
+<!-- YAML
+added: REPLACEME
+-->
+
+An attempt was made to import a module without an assertion that requires
+a specific import assertion to be loaded.
+
 <a id="ERR_MISSING_OPTION"></a>
 ### `ERR_MISSING_OPTION`
 

doc/api/esm.md

@@ -7,6 +7,9 @@
 <!-- YAML
 added: v8.5.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/39921
+    description: Add support for import assertions.
   - version:
     - REPLACEME
     pr-url: https://github.com/nodejs/node/pull/37468
@@ -232,6 +235,25 @@ absolute URL strings.
 import fs from 'node:fs/promises';
 ```
 
+## Import assertions
+<!-- YAML
+added: REPLACEME
+-->
+
+The [Import Assertions proposal][] adds an inline syntax for module import
+statements to pass on more information alongside the module specifier.
+
+```js
+import json from './foo.json' assert { type: "json" };
+await import('foo.json', { assert: { type: "json" } });
+```
+
+Node.js supports the following `type` values:
+
+| `type`   | Resolves to      |
+| -------- | ---------------- |
+| `"json"` | [JSON modules][] |
+
 ## Builtin modules
 
 [Core modules][] provide named exports of their public API. A
@@ -522,9 +544,8 @@ same path.
 
 Assuming an `index.mjs` with
 
-<!-- eslint-skip -->
 ```js
-import packageConfig from './package.json';
+import packageConfig from './package.json' assert { type: 'json' };
 ```
 
 The `--experimental-json-modules` flag is needed for the module
@@ -610,18 +631,26 @@ CommonJS modules loaded.
 ### Hooks
 
 #### `resolve(specifier, context, defaultResolve)`
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: TBD
+    description: Add support for import assertions.
+-->
 
 > Note: The loaders API is being redesigned. This hook may disappear or its
 > signature may change. Do not rely on the API described below.
 
 * `specifier` {string}
 * `context` {Object}
   * `conditions` {string[]}
+  * `importAssertions` {Object}
   * `parentURL` {string|undefined}
 * `defaultResolve` {Function} The Node.js default resolver.
 * Returns: {Object}
   * `format` {string|null|undefined}
     `'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'`
+  * `importAssertions` {Object}
   * `url` {string} The absolute url to the import target (such as `file://…`)
 
 The `resolve` hook returns the resolved file URL for a given module specifier
@@ -1350,6 +1379,8 @@ success!
 [Dynamic `import()`]: https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports
 [ECMAScript Top-Level `await` proposal]: https://github.com/tc39/proposal-top-level-await/
 [ES Module Integration Proposal for Web Assembly]: https://github.com/webassembly/esm-integration
+[Import Assertions proposal]: https://github.com/tc39/proposal-import-assertions
+[JSON modules]: #json-modules
 [Node.js Module Resolution Algorithm]: #resolver-algorithm-specification
 [Terminology]: #terminology
 [URL]: https://url.spec.whatwg.org/

lib/internal/errors.js

@@ -953,6 +953,9 @@ E('ERR_ENCODING_NOT_SUPPORTED', 'The "%s" encoding is not supported',
   RangeError);
 E('ERR_EVAL_ESM_CANNOT_PRINT', '--print cannot be used with ESM input', Error);
 E('ERR_EVENT_RECURSION', 'The event "%s" is already being dispatched', Error);
+E('ERR_FAILED_IMPORT_ASSERTION', (request, key, expectedValue, actualValue) => {
+  return `Failed to load module "${request}", expected ${key} to be ${JSONStringify(expectedValue)}, got ${JSONStringify(actualValue)} instead`;
+}, TypeError);
 E('ERR_FALSY_VALUE_REJECTION', function(reason) {
   this.reason = reason;
   return 'Promise was rejected with falsy value';
@@ -1250,6 +1253,9 @@ E('ERR_INVALID_FILE_URL_HOST',
 E('ERR_INVALID_FILE_URL_PATH', 'File URL path %s', TypeError);
 E('ERR_INVALID_HANDLE_TYPE', 'This handle type cannot be sent', TypeError);
 E('ERR_INVALID_HTTP_TOKEN', '%s must be a valid HTTP token ["%s"]', TypeError);
+E('ERR_INVALID_IMPORT_ASSERTION',
+  (type, value) => `Invalid ${JSONStringify(type)} import assertion: ${JSONStringify(value)}`,
+  TypeError);
 E('ERR_INVALID_IP_ADDRESS', 'Invalid IP address: %s', TypeError);
 E('ERR_INVALID_MODULE_SPECIFIER', (request, reason, base = undefined) => {
   return `Invalid module "${request}" ${reason}${base ?
@@ -1394,6 +1400,9 @@ E('ERR_MISSING_ARGS',
     }
     return `${msg} must be specified`;
   }, TypeError);
+E('ERR_MISSING_IMPORT_ASSERTION',
+  'Failed to load %s: Node.js requires modules of format "%s" to be loaded ' +
+  'using an assertion "%s" with value "%s"', TypeError);
 E('ERR_MISSING_OPTION', '%s is required', TypeError);
 E('ERR_MODULE_NOT_FOUND', (path, base, type = 'package') => {
   return `Cannot find ${type} '${path}' imported from ${base}`;

lib/internal/modules/cjs/loader.js

@@ -1015,9 +1015,10 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       filename,
       lineOffset: 0,
       displayErrors: true,
-      importModuleDynamically: async (specifier) => {
+      importModuleDynamically: async (specifier, _, importAssertions) => {
         const loader = asyncESM.esmLoader;
-        return loader.import(specifier, normalizeReferrerURL(filename));
+        return loader.import(specifier, normalizeReferrerURL(filename),
+                             importAssertions);
       },
     });
   }
@@ -1030,9 +1031,10 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       '__dirname',
     ], {
       filename,
-      importModuleDynamically(specifier) {
+      importModuleDynamically(specifier, _, importAssertions) {
         const loader = asyncESM.esmLoader;
-        return loader.import(specifier, normalizeReferrerURL(filename));
+        return loader.import(specifier, normalizeReferrerURL(filename),
+                             importAssertions);
       },
     });
   } catch (err) {