[WIP Prototype] ES6 https://html.spec.whatwg.org/#fetch-a-single-module-script implementation

third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp

+// Copyright 2017 The Chromium Authors. All rights reserved.

[dominicc (has gone to gerrit), 2017/01/11 06:57:15]

WDYT about making some of the DCHECKs in this class CHECKs? It will make it
easier to detect faults in the wild through crash/

[kouhei (in TOK), 2017/01/17 05:26:13]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/loader/modulescript/ModuleTreeLinker.h"
+
+#include "bindings/core/v8/ScriptModule.h"
+#include "core/dom/ModuleScript.h"
+#include "core/loader/modulescript/ModuleTreeLinkerRegistry.h"
+
+namespace blink {
+
+ModuleTreeLinker* ModuleTreeLinker::fetch(const KURL& url,
+                                          const KURL& baseURL,
+                                          HashSet<KURL> ancestorList,
+                                          Modulator* modulator,
+                                          ModuleTreeLinkerRegistry* registry,
+                                          ModuleTreeClient* client) {
+  HashSet<KURL> ancestorListWithUrl = ancestorList;
+  ancestorListWithUrl.add(url);
+
+  ModuleTreeLinker* fetcher = new ModuleTreeLinker(
+      std::move(ancestorListWithUrl), modulator, registry, client);
+  fetcher->fetchSelf(url, baseURL);
+  return fetcher;
+}
+
+ModuleTreeLinker::ModuleTreeLinker(HashSet<KURL> ancestorListWithUrl,
+                                   Modulator* modulator,
+                                   ModuleTreeLinkerRegistry* registry,
+                                   ModuleTreeClient* client)
+    : m_modulator(modulator),
+      m_registry(registry),
+      m_client(client),
+      m_ancestorListWithUrl(std::move(ancestorListWithUrl)) {
+  DCHECK(modulator);
+  DCHECK(registry);
+  DCHECK(client);
+}
+
+DEFINE_TRACE(ModuleTreeLinker) {
+  visitor->trace(m_modulator);
+  visitor->trace(m_registry);
+  visitor->trace(m_client);
+  visitor->trace(m_moduleScript);
+  visitor->trace(m_dependencyClients);
+  SingleModuleClient::trace(visitor);
+}
+
+void ModuleTreeLinker::advanceState(State newState) {
+  printf("mtf %p adv state: %d\n", this, newState);
+  switch (m_state) {
+    case State::Initial:
+      DCHECK_EQ(newState, State::FetchingSelf);
+      break;
+    case State::FetchingSelf:
+      DCHECK(newState == State::FetchingDependencies ||
+             newState == State::Finished);
+      break;
+    case State::FetchingDependencies:
+      DCHECK(newState == State::Instantiating || newState == State::Finished);
+      break;
+    case State::Instantiating:
+      DCHECK_EQ(newState, State::Finished);
+      break;
+    case State::Finished:
+      NOTREACHED();
+      break;
+    default:
+      NOTREACHED();

[dominicc (has gone to gerrit), 2017/01/11 06:57:15]

Is there other state which can be DCHECKed at these transitions, like
m_numIncompleteDescendants?

[kouhei (in TOK), 2017/01/17 05:26:13]

Done.

+  }
+
+  m_state = newState;
+
+  if (m_state == State::Finished) {
+    m_registry->releaseFinishedFetcher(this);
+    m_client->notifyFinishedModuleTree(m_moduleScript);
+  }
+}
+
+void ModuleTreeLinker::fetchSelf(const KURL& url, const KURL& baseURL) {
+  // https://html.spec.whatwg.org/multipage/webappapis.html#internal-module-script-graph-fetching-procedure
+
+  // Step 1. Fetch a single module script given url, fetch client settings
+  // object, destination, cryptographic nonce, parser state, credentials mode,
+  // module map settings object, referrer, and the top-level module fetch flag.
+  // If the caller of this algorithm specified custom perform the fetch steps,
+  // pass those along while fetching a single module script.
+  // Step 2. Return from this algorithm, and run the following steps when
+  // fetching a single module script asynchronously completes with result.
+  advanceState(State::FetchingSelf);
+  m_modulator->fetchSingle(url, baseURL, this);
+}
+
+class ModuleTreeLinker::DependencyModuleClient
+    : public GarbageCollectedFinalized<
+          ModuleTreeLinker::DependencyModuleClient>,
+      public ModuleTreeClient {
+  USING_GARBAGE_COLLECTED_MIXIN(ModuleTreeLinker::DependencyModuleClient);
+
+ public:
+  static DependencyModuleClient* create(ModuleTreeLinker* moduleTreeLinkers) {
+    return new DependencyModuleClient(moduleTreeLinkers);
+  }
+  virtual ~DependencyModuleClient() = default;
+
+  DEFINE_INLINE_TRACE() {
+    visitor->trace(m_moduleTreeLinkers);
+    ModuleTreeClient::trace(visitor);
+  }
+
+ private:
+  DependencyModuleClient(ModuleTreeLinker* moduleTreeLinkers)
+      : m_moduleTreeLinkers(moduleTreeLinkers) {
+    DCHECK(moduleTreeLinkers);
+  }
+
+  // Implements ModuleTreeClient
+  void notifyFinishedModuleTree(ModuleScript*) override;
+
+  Member<ModuleTreeLinker> m_moduleTreeLinkers;
+};
+
+void ModuleTreeLinker::notifyFinishedSingleModule(ModuleScript* moduleScript) {
+  // https://html.spec.whatwg.org/multipage/webappapis.html#internal-module-script-graph-fetching-procedure
+
+  // Step 3. If result is null, asynchronously complete this algorithm with null
+  // and abort these steps.
+  if (!moduleScript) {
+    advanceState(State::Finished);
+    return;
+  }
+
+  // Step 4. Otherwise, result is a module script. Fetch the descendants of
+  // result given destination and an ancestor list obtained by appending url to
+  // ancestor list. Wait for fetching the descendants of a module script to
+  // asynchronously complete with descendants result before proceeding to the
+  // next step.
+  m_moduleScript = moduleScript;
+  fetchDescendants();
+
+  // Note: Step 5- continues in instantiate() method, after
+  // "fetch the descendants of a module script" procedure completes.
+}
+
+void ModuleTreeLinker::fetchDescendants() {
+  DCHECK(m_moduleScript);
+  advanceState(State::FetchingDependencies);
+
+  // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-the-descendants-of-a-module-script
+
+  // Step 1. Let record be module script's module record.
+  ScriptModule record = m_moduleScript->record();
+
+  // Step 2. If record.[[RequestedModules]] is empty, asynchronously complete
+  // this algorithm with module script.
+  Vector<String> moduleRequests =
+      m_modulator->moduleRequestsFromScriptModule(record);
+  if (moduleRequests.isEmpty()) {
+    // Continue to instantiate() to process "internal module script graph
+    // fetching procedure" Step 5-.
+    instantiate();
+    return;
+  }
+
+  // Step 3. Let urls be a new empty list.
+  Vector<KURL> urls;
+
+  // Step 4. For each string requested of record.[[RequestedModules]],
+  for (const auto& moduleRequest : moduleRequests) {
+    // Step 4.1. Let url be the result of resolving a module specifier given
+    // module script and requested.
+    KURL url = m_modulator->resolveModuleSpecifier(moduleRequest,
+                                                   m_moduleScript->baseURL());
+    printf("resolveModuleSpecifier \"%s\" -> \"%s\"\n",
+           moduleRequest.utf8().data(), url.getString().utf8().data());
+
+    // Step 4.2. If the result is error: ...
+    if (url.isNull()) {
+      // Let error be a new TypeError exception.

[dominicc (has gone to gerrit), 2017/01/11 06:57:15]

TODO might be useful here to keep track.

[kouhei (in TOK), 2017/01/17 05:26:13]

Done.

+      // Report the exception error for module script.
+      // Abort this algorithm, and asynchronously complete it with null.
+      m_moduleScript = nullptr;
+      advanceState(State::Finished);
+    }
+
+    // Step 4.3. Otherwise, if ancestor list does not contain url, append url to
+    // urls.
+
+    // Modulator::resolveModuleSpecifier() impl must return either a valid url
+    // or null.
+    DCHECK(url.isValid());
+    if (!m_ancestorListWithUrl.contains(url))
+      urls.push_back(url);
+  }
+
+  // Step 5. For each url in urls, perform the internal module script graph
+  // fetching procedure given url, module script's credentials mode, module
+  // script's cryptographic nonce, module script's parser state, destination,
+  // module script's settings object, module script's settings object, ancestor
+  // list, module script's base URL, and with the top-level module fetch flag
+  // unset. If the caller of this algorithm specified custom perform the fetch
+  // steps, pass those along while performing the internal module script graph
+  // fetching procedure.
+  DCHECK_EQ(m_numIncompleteDescendants, 0u);
+  m_numIncompleteDescendants = urls.size();
+  for (const KURL& url : urls) {
+    DependencyModuleClient* dependencyClient =
+        DependencyModuleClient::create(this);
+    m_dependencyClients.add(dependencyClient);
+    m_modulator->fetchTree(url, m_moduleScript->baseURL(), dependencyClient);
+  }
+
+  // Asynchronously continue processing after notifyOneDescendantFinished() is
+  // called m_numIncompleteDescendants times.
+  DCHECK(m_numIncompleteDescendants);
+}
+
+void ModuleTreeLinker::DependencyModuleClient::notifyFinishedModuleTree(
+    ModuleScript* moduleScript) {
+  bool wasSuccess = !!moduleScript;
+  m_moduleTreeLinkers->notifyOneDescendantFinished(wasSuccess);
+}
+
+void ModuleTreeLinker::notifyOneDescendantFinished(bool wasSuccess) {
+  if (m_state == State::Finished) {
+    // We may reach here if one of the descendant failed to load, and the other
+    // descendants fetches were in flight.
+    DCHECK(!m_moduleScript);
+    return;
+  }
+
+  DCHECK_EQ(m_state, State::FetchingDependencies);
+
+  DCHECK_GT(m_numIncompleteDescendants, 0u);
+  --m_numIncompleteDescendants;
+
+  if (!wasSuccess) {
+    m_moduleScript = nullptr;
+    advanceState(State::Finished);
+    return;
+  }
+
+  DCHECK(m_moduleScript);
+  printf("remaining desc %zu\n", m_numIncompleteDescendants);
+  if (!m_numIncompleteDescendants)
+    instantiate();
+}
+
+void ModuleTreeLinker::instantiate() {
+  DCHECK(m_moduleScript);
+  advanceState(State::Instantiating);
+
+  // https://html.spec.whatwg.org/multipage/webappapis.html#internal-module-script-graph-fetching-procedure
+
+  // Step 5. Let record be result's module record.
+  ScriptModule record = m_moduleScript->record();
+
+  // Step 6. Let instantiationStatus be record.ModuleDeclarationInstantiation().
+  bool instantiateSuccess = m_modulator->instantiateModule(record);
+  DCHECK(instantiateSuccess);  // TODO(kouhei)
+  m_moduleScript->updateStateAfterInstantiation(ScriptValue());
+  InstantiationState instantiationStatus = m_moduleScript->instantiationState();
+
+  // Step 7. For each module script script in result's uninstantiated inclusive
+  // descendant module scripts, perform the following steps:
+  HeapHashSet<Member<ModuleScript>> uninstantiatedSet =
+      uninstantiatedInclusiveDescendants();
+  for (const auto& descendant : uninstantiatedSet) {
+    if (instantiationStatus == InstantiationState::Errored) {
+      // Step 7.1. If instantiationStatus is an abrupt completion, then set
+      // script's
+      // instantiation state to "errored", its instantiation error to
+      // instantiationStatus.[[Value]], and its module record to null.
+      descendant->propagateUpstreamError(m_moduleScript->instantiationError());
+    } else {
+      // Step 7.2. Otherwise, set script's instantiation state to
+      // "instantiated".
+      descendant->propagateUpstreamSuccess();
+    }
+  }
+
+  // Step 8. Asynchronously complete this algorithm with descendants result.
+  advanceState(State::Finished);
+}
+
+HeapHashSet<Member<ModuleScript>>
+ModuleTreeLinker::uninstantiatedInclusiveDescendants() {
+  // https://html.spec.whatwg.org/multipage/webappapis.html#uninstantiated-inclusive-descendant-module-scripts
+  // Step 1. Let moduleMap be script's settings object's module map.
+  // Note: Modulator is our "settings object".
+  // Note: We won't reference the ModuleMap directly here to aid testing.
+
+  // Step 2. Let stack be the stack « script ».
+  HeapDeque<Member<ModuleScript>> stack;
+  stack.prepend(m_moduleScript);
+
+  // Step 3. Let inclusive descendants be an empty set.
+  // Note: We use unordered set here as the order is not observable from web
+  // platform.
+  // This is allowed per spec: https://infra.spec.whatwg.org/#sets
+  HeapHashSet<Member<ModuleScript>> inclusiveDescendants;
+
+  // Step 4. While stack is not empty:
+  while (!stack.isEmpty()) {
+    // Step 4.1. Let current the result of popping from stack.
+    ModuleScript* current = stack.takeFirst();
+
+    // Step 4.2. If inclusive descendants and stack both do not contain current,
+    // then:
+    if (inclusiveDescendants.contains(current))
+      continue;
+    if (std::find(stack.begin(), stack.end(), current) != stack.end())

[dominicc (has gone to gerrit), 2017/01/11 06:57:15]

How deep does this get? Would it make sense to have a second set for what's on
the stack?

[kouhei (in TOK), 2017/01/17 05:26:13]

Added a TODO.
uninstantiatedInclusiveDescendants() method has a lot of room for optimization.
We should propose optimization to the spec algorithm too.

+      continue;
+
+    // Step 4.2.1. Append current to inclusive descendants.
+    inclusiveDescendants.add(current);
+
+    // TODO(kouhei): This implementation is a direct transliteration of the
+    // spec. Omit intermediate vectors at the least.
+
+    // Step 4.2.2. Let child specifiers be the value of current's module
+    // record's [[RequestedModules]] internal slot.
+    Vector<String> childSpecifiers =
+        m_modulator->moduleRequestsFromScriptModule(current->record());
+    // Step 4.2.3. Let child URLs be the list obtained by calling resolve a
+    // module specifier once for each item of child specifiers, given current
+    // and that item. Omit any failures.
+    Vector<KURL> childURLs;
+    for (const auto& childSpecifier : childSpecifiers) {
+      KURL childURL = m_modulator->resolveModuleSpecifier(childSpecifier,
+                                                          current->baseURL());
+      if (childURL.isValid())
+        childURLs.push_back(childURL);
+    }
+    // Step 4.2.4. Let child modules be the list obtained by getting each value
+    // in moduleMap whose key is given by an item of child URLs.
+    HeapVector<Member<ModuleScript>> childModules;
+    for (const auto& childURL : childURLs) {
+      ModuleScript* moduleScript =
+          m_modulator->retrieveFetchedModuleScript(childURL);
+      childModules.push_back(moduleScript);
+    }
+    // Step 4.2.5. For each s in child modules that is not contained by
+    // inclusive descendants, push s onto stack.
+    for (const auto& s : childModules) {
+      if (!inclusiveDescendants.contains(s))
+        stack.prepend(s);
+    }
+  }
+
+  // Step 5. Return a set containing all items of inclusive descendants whose
+  // instantiation state is "uninstantiated".
+  HeapHashSet<Member<ModuleScript>> uninstantiatedSet;
+  for (const auto& script : inclusiveDescendants) {
+    if (script->instantiationState() == InstantiationState::Uninstantiated)
+      uninstantiatedSet.add(script);
+  }
+  return uninstantiatedSet;
+}
+
+}  // namespace blink