Don't cache HTTP errors in the module map

Multiple parallel imports will still only fetch once, and if the fetch fails, will both error. A subsequent import (dynamic import, a dynamically inserted via `<script src="..." type="module">`, or a static import from either of these) to the same specifier will result in a re-fetch if the previous fetch failed.

Tests: web-platform-tests/wpt#55505

Fixes #6768.

Co-authored-by: Yoav Weiss <yoav.weiss@shopify.com>

Author: lucacasonato

source

@@ -118847,17 +118847,16 @@ document.querySelector("button").addEventListener("click", bound);
    <li><p>Let <var>moduleMap</var> be <var>settingsObject</var>'s <span
    data-x="concept-settings-object-module-map">module map</span>.</p></li>
 
-   <li><p>If <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)] is
-   "<code data-x="">fetching</code>", wait <span>in parallel</span> until that entry's value
-   changes, then <span>queue a task</span> on the <span>networking task source</span> to proceed
-   with running the following steps.</p></li>
+   <li><p>If <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)] is a
+   <span>module script</span> or null, run <var>onComplete</var> given
+   <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)], and return.</p></li>
 
-   <li><p>If <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)] <span
-   data-x="map exists">exists</span>, run <var>onComplete</var> given
+   <li><p>If <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)] is a <span>list</span>,
+   <span data-x="list append">append</span> <var>onComplete</var> to
    <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)], and return.</p></li>
 
    <li><p><span data-x="map set">Set</span> <var>moduleMap</var>[(<var>url</var>,
-   <var>moduleType</var>)] to "<code data-x="">fetching</code>".</p></li>
+   <var>moduleType</var>)] to « <var>onComplete</var> ».</p></li>
 
    <li><p>Let <var>request</var> be a new <span data-x="concept-request">request</span> whose
    <span data-x="concept-request-url">URL</span> is <var>url</var>, <span
@@ -118911,9 +118910,20 @@ document.querySelector("button").addEventListener("click", bound);
        <span>ok status</span>,</p></li>
       </ul>
 
-      <p>then <span data-x="map set">set</span> <var>moduleMap</var>[(<var>url</var>,
-      <var>moduleType</var>)] to null, run <var>onComplete</var> given null, and abort these
-      steps.</p>
+      <p>then:</p>
+
+      <ol>
+       <li><p>Let <var>callbacks</var> be
+       <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)].</p></li>
+
+       <li><p><span data-x="map remove">Remove</span>
+       <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)].</p></li>
+
+       <li><p><span data-x="list iterate">For each</span> <var>callback</var> of
+       <var>callbacks</var>: run <var>callback</var> given null.</p></li>
+
+       <li><p>Return.</p></li>
+      </ol>
      </li>
 
      <li><p>Let <var>mimeType</var> be the result of <span data-x="extract a MIME type">extracting
@@ -118965,17 +118975,24 @@ document.querySelector("button").addEventListener("click", bound);
       </ol>
      </li>
 
+     <li><p>Let <var>callbacks</var> be
+     <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)].</p></li>
+
      <li>
-      <p><span data-x="map set">Set</span> <var>moduleMap</var>[(<var>url</var>,
-      <var>moduleType</var>)] to <var>moduleScript</var>, and run <var>onComplete</var> given
-      <var>moduleScript</var>.</p>
+      <p>If <var>moduleScript</var> is null, then <span data-x="map remove">remove</span>
+      <var>moduleMap</var>[(<var>url</var>, <var>moduleType</var>)]; otherwise
+      <span data-x="map set">set</span> <var>moduleMap</var>[(<var>url</var>,
+      <var>moduleType</var>)] to <var>moduleScript</var>.</p>
 
       <p class="note">It is intentional that the <span>module map</span> is keyed by the <span
       data-x="concept-request-url">request URL</span>, whereas the <span
       data-x="concept-script-base-url">base URL</span> for the <span>module script</span> is
       set to the <span data-x="concept-response-url">response URL</span>. The former is used to
       deduplicate fetches, while the latter is used for URL resolution.</p>
      </li>
+
+     <li><p><span data-x="list iterate">For each</span> <var>callback</var> of
+     <var>callbacks</var>: run <var>callback</var> given <var>moduleScript</var>.</p></li>
     </ol>
    </li>
   </ol>
@@ -121933,11 +121950,12 @@ dictionary <dfn dictionary>PromiseRejectionEventInit</dfn> : <span>EventInit</sp
   data-x="tuple">tuples</span> consisting of a <span>URL record</span> and a <span>string</span>.
   The <span>URL record</span> is the <span data-x="concept-request-url">request URL</span> at which
   the module was fetched, and the <span>string</span> indicates the type of the module (e.g. "<code
-  data-x="">javascript-or-wasm</code>"). The <span>module map</span>'s values are either a
-  <span>module script</span>, null (used to represent failed fetches), or a placeholder value "<code
-  data-x="">fetching</code>". </span><span data-x="module map">Module maps</span> are used to ensure
-  that imported module scripts are only fetched, parsed, and evaluated once per
-  <code>Document</code> or <a href="#workers">worker</a>.</p>
+  data-x="">javascript-or-wasm</code>"). The <span>module map</span>'s values are either a <span>module
+  script</span>, null (used to represent a mismatched <span>MIME type</span>), or a
+  <span>list</span> of algorithms (that are waiting for the fetch to complete).</span> <span
+  data-x="module map">Module maps</span> are used to ensure that imported module scripts are only
+  fetched, parsed, and evaluated once per <code>Document</code> or <a
+  href="#workers">worker</a>.</p>
 
   <div class="example">
    <p>Since <span data-x="module map">module maps</span> are keyed by (URL, module type), the
@@ -162005,6 +162023,7 @@ INSERT INTERFACES HERE
   Logan Moore,
   Lorenz Ackermann,
   Loune,
+  Luca Casonato,
   Lucas Gadani,
   &#x0141;ukasz Pilorz,
   Luke Kenneth Casson Leighton,