Multiple import maps

Import maps currently have to load before any ES module and there can
only be a single import map per document. That makes them fragile and
potentially slow to use in real-life scenarios: Any module that loads
before them breaks the entire app, and in apps with many modules the
become a large blocking resource, as the entire map for all possible
modules needs to load first.

This implements whatwg/html#10528 to solve that.

Change-Id: I54e1b9cdfe989d61c85d73a5fd384f860273ad9a
Bug: 358379381
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5776262
Commit-Queue: Yoav Weiss (@Shopify) <[email protected]>
Reviewed-by: Kouhei Ueno <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1378943}

import-maps/acquiring/dynamic-import.html

@@ -3,8 +3,6 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-const t = async_test(
-  'After dynamic imports, import maps should fire error events');
 const log = [];
 // To ensure we are testing that the flag is cleared at the beginning of module
 // script loading unconditionally, not at the end of loading or not at the
@@ -14,7 +12,7 @@
 promise_test(() => import('../resources/empty.js?pipe=trickle(d1)'),
              "A dynamic import succeeds");
 </script>
-<script type="importmap" onload="t.assert_unreached('onload')" onerror="t.done()">
+<script type="importmap">
 {
   "imports": {
     "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B"
@@ -24,7 +22,6 @@
 <script>
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
-    .then(() => assert_array_equals(log, ["log:A"]))
-  },
-  'After a dynamic import(), import maps are not effective');
+    .then(() => assert_array_equals(log, ["log:B"]))
+  }, 'After a dynamic import(), import maps work fine');
 </script>

import-maps/acquiring/modulepreload-link-header.html

@@ -3,11 +3,9 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-const t = async_test(
-  'With modulepreload link header, import maps should fire error events');
 const log = [];
 </script>
-<script type="importmap" onerror="t.done()">
+<script type="importmap">
 {
   "imports": {
     "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B"
@@ -17,7 +15,7 @@
 <script>
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
-    .then(() => assert_array_equals(log, ["log:A"]))
+    .then(() => assert_array_equals(log, ["log:B"]))
   },
-  'With modulepreload link header, import maps are not effective');
+  'With modulepreload link header, import maps work fine');
 </script>

import-maps/acquiring/modulepreload.html

@@ -3,12 +3,10 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-const t = async_test(
-  'After <link rel=modulepreload> import maps should fire error events');
 const log = [];
 </script>
 <link rel="modulepreload" href="../resources/empty.js?pipe=trickle(d1)"></link>
-<script type="importmap" onerror="t.done()">
+<script type="importmap">
 {
   "imports": {
     "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B"
@@ -18,7 +16,7 @@
 <script>
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
-    .then(() => assert_array_equals(log, ["log:A"]))
+    .then(() => assert_array_equals(log, ["log:B"]))
   },
-  'After <link rel=modulepreload> import maps are not effective');
+  'After <link rel=modulepreload> import maps should work fine');
 </script>

import-maps/acquiring/script-tag-inline.html

@@ -3,18 +3,11 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-const t = async_test(
-  'After inline <script type="module"> import maps should fire error events');
 const log = [];
 </script>
 <script type="module">
-// While this inline module script doesn't have any specifiers and doesn't fetch
-// anything, this still disables subsequent import maps, because
-// https://wicg.github.io/import-maps/#wait-for-import-maps
-// is anyway called at the beginning of
-// https://html.spec.whatwg.org/multipage/webappapis.html#fetch-an-inline-module-script-graph
 </script>
-<script type="importmap" onerror="t.done()">
+<script type="importmap">
 {
   "imports": {
     "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B"
@@ -24,7 +17,7 @@
 <script>
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
-    .then(() => assert_array_equals(log, ["log:A"]))
+    .then(() => assert_array_equals(log, ["log:B"]))
   },
-  'After inline <script type="module"> import maps are not effective');
+  'After inline <script type="module"> import maps work fine');
 </script>

import-maps/acquiring/script-tag.html

@@ -3,12 +3,10 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-const t = async_test(
-  'After <script type="module"> import maps should fire error events');
 const log = [];
 </script>
 <script type="module" src="../resources/empty.js?pipe=trickle(d1)"></script>
-<script type="importmap" onerror="t.done()">
+<script type="importmap">
 {
   "imports": {
     "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B"
@@ -18,7 +16,7 @@
 <script>
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
-    .then(() => assert_array_equals(log, ["log:A"]))
+    .then(() => assert_array_equals(log, ["log:B"]))
   },
-  'After <script type="module"> import maps are not effective');
+  'After <script type="module"> import maps work fine');
 </script>

import-maps/multiple-import-maps/already-resolved-dropped.html

@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/import-maps/resources/test-helper.js"></script>
+<script>
+// Simulate resolving a module before import maps are processed
+import("../resources/log.js?pipe=sub&name=ModuleA").catch(() => {});
+</script>
+<script type="importmap">
+{
+   "imports": {
+    "../resources/log.js?pipe=sub&name=ModuleA": "../resources/log.js?pipe=sub&name=ModuleB",
+    "http:/": "../resources/log.js?pipe=sub&name=scheme",
+    "https:/": "../resources/log.js?pipe=sub&name=scheme"
+  }
+}
+</script>
+<script>
+test_loaded(
+  "../resources/log.js?pipe=sub&name=ModuleA",
+  ["log:ModuleA"],
+  "Rules for already resolved modules are dropped"
+);
+</script>
+</html>

import-maps/multiple-import-maps/basic.html

@@ -22,15 +22,13 @@
 }
 </script>
 <script>
-// Currently the spec doesn't allow multiple import maps, by setting acquiring
-// import maps to false on preparing the first import map.
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A1")
     .then(() => import("../resources/log.js?pipe=sub&name=A2"))
     .then(() => import("../resources/log.js?pipe=sub&name=A3"))
     .then(() => assert_array_equals(
                     log,
-                    ["onerror 2", "log:B1", "log:B2", "log:A3"]))
+                    ["log:B1", "log:B2", "log:C3"]))
   },
-  "Second import map should be rejected");
+  "Second import map should be used for resolution");
 </script>

import-maps/multiple-import-maps/conflict-first-persists.html

@@ -0,0 +1,49 @@
+<!DOCTYPE html>
+<html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script type="importmap">
+{
+   "imports": {
+    "module-a": "../resources/log.js?pipe=sub&name=ModuleA",
+    "module-b/something": "../resources/log.js?pipe=sub&name=ModuleB"
+  }
+}
+</script>
+<script type="importmap">
+{
+  "imports": {
+    "module-a": "../resources/log.js?pipe=sub&name=OtherModuleA",
+    "module-b/": "../resources/log.js?pipe=sub&name=PrefixModuleB",
+    "module-b": "../resources/log.js?pipe=sub&name=OtherModuleB"
+  }
+}
+</script>
+<script>
+const test_loaded = (specifier, expected_log, description) => {
+  promise_test(async t => {
+    log = [];
+    await import(specifier);
+    assert_array_equals(log, expected_log);
+  }, description);
+};
+
+test_loaded(
+  "module-a",
+  ["log:ModuleA"],
+  "First defined rule persists in case of conflict"
+);
+
+test_loaded(
+  "module-b/something",
+  ["log:ModuleB"],
+  "First defined rule persists in case of conflict - prefixed bare specifiers"
+);
+
+test_loaded(
+  "module-b",
+  ["log:OtherModuleB"],
+  "First defined rule persists in case of conflict - non-prefix bare specifier"
+);
+</script>
+</html>

import-maps/multiple-import-maps/resolution-consistency-in-module-tree-inline.html

@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<script>
+function waitForBool(boolName) {
+  return new Promise((resolve) => {
+    const checkVariable = setInterval(() => {
+      if (window[boolName]) {
+        clearInterval(checkVariable);
+        resolve();
+      }
+    }, 0);
+  });
+}
+
+step_timeout(() => {
+  const importMapScript = document.createElement('script');
+  importMapScript.type = 'importmap';
+  importMapScript.textContent = JSON.stringify({
+    imports: {
+      "../resources/log.sub.js?name=A": "../resources/log.sub.js?name=B"
+    }
+  });
+  document.head.appendChild(importMapScript);
+}, 100);
+const log = [];
+</script>
+<script type="module">
+import "../resources/importer.sub.js?pipe=trickle(d0.5)&name=..%2Fresources%2Flog.sub.js%3Fname%3DA";
+</script>
+<script type="module">
+test(() => {
+  assert_array_equals(log, ["log:B"], "Import should use the new import map");
+}, "Module tree that started to download before a new import map should still take it into account");
+</script>
+</body>
+</html>
+
+
+
+

import-maps/multiple-import-maps/resolution-consistency-in-module-tree.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<script type="module" async>
+step_timeout(() => {
+  const importMapScript = document.createElement('script');
+  importMapScript.type = 'importmap';
+  importMapScript.textContent = JSON.stringify({
+    imports: {
+      "../resources/log.sub.js?name=A": "../resources/log.sub.js?name=B"
+    }
+  });
+  document.head.appendChild(importMapScript);
+}, 100);
+</script>
+<script>
+const log = [];
+</script>
+<script type="module" src="../resources/importer.sub.js?pipe=trickle(d0.5)&name=..%2Fresources%2Flog.sub.js%3Fname%3DA"></script>
+<script type="module">
+test(() => {
+  assert_array_equals(log, ["log:B"], "Import should use the new import map");
+}, "Module tree that started to download before a new import map should still take it into account");
+</script>
+</body>
+</html>
+
+
+

import-maps/multiple-import-maps/url-resolution-conflict.html

@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+const log = [];
+</script>
+<script type="importmap">
+{
+  "scopes": {
+    "/": {
+      "../resources/../resources/app.js": "../resources/log.js?pipe=sub&name=first"
+    }
+  }
+}
+</script>
+<script type="importmap">
+{
+  "scopes": {
+    "/": {
+      "../resources/app.js": "../resources/log.js?pipe=sub&name=second"
+    }
+  }
+}
+</script>
+<script type="module">
+promise_test(async () => {
+  await import("../resources/app.js");
+  assert_array_equals(log, ["log:first"]);
+},
+"Second import map should not override same resolved URL");
+</script>

import-maps/multiple-import-maps/with-errors.html

@@ -18,15 +18,11 @@
 }
 </script>
 <script>
-// Currently the spec doesn't allow multiple import maps, by setting acquiring
-// import maps to false on preparing the first import map.
-// Even the first import map has errors and thus Document's import map is not
-// updated, the second import map is still rejected at preparationg.
 promise_test(() => {
   return import("../resources/log.js?pipe=sub&name=A")
     .then(() => assert_array_equals(
                     log,
-                    ["onerror 2", "log:A"]))
+                    ["log:C"]))
   },
-  "Second import map should be rejected after an import map with errors");
+  "Second import map should be used for resolution even after an import map with errors");
 </script>

import-maps/not-overridden/dynamic.html

@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<script>
+const log = [];
+
+// First, use a module specifier
+promise_test(() => {
+  return import("../resources/log.js?pipe=sub&name=A")
+    .then(() => {
+      assert_array_equals(log, ["log:A"], "First import should use original module");
+    });
+}, "Initial import before import map");
+
+// Now try to redefine it with multiple import map rules
+</script>
+<script type="importmap">
+{
+  "imports": {
+    "../resources/log.js?pipe=sub&name=A": "../resources/log.js?pipe=sub&name=B",
+    "http:/": "../resources/log.js?pipe=sub&name=scheme",
+    "https:/": "../resources/log.js?pipe=sub&name=scheme"
+  }
+}
+</script>
+<script type="module">
+// Testing that the resolution is correct using `resolve`, as you can't import
+// the same module twice.
+test(() => {
+  assert_true(import.meta.resolve("../resources/log.js?pipe=sub&name=A")
+              .endsWith("/resources/log.js?pipe=sub&name=A"));
+}, "Resolution after import map should not be redefined");
+</script>
+</body>
+</html>
+