Bug 1513366: Part 1 - Add do_ImportModule helper for importing JS modules. r=mccr8

This helper makes it considerably easier for C++ code to import a JS module
and wrap it in an appropriately-defined XPIDL interface for its exports.
Typical usage is something like:

Foo.jsm:

  var EXPORTED_SYMBOLS = ["foo"];

  function foo(bar) {
    return bar.toString();
  }

mozIFoo.idl:

  interface mozIFoo : nsISupports {
    AString foo(double meh);
  }

Thing.cpp:

  nsCOMPtr<mozIFoo> foo = do_ImportModule(
    "resource://meh/Foo.jsm");

  MOZ_TRY(foo->Foo(42));

Differential Revision: https://phabricator.services.mozilla.com/D14209

--HG--
extra : rebase_source : 4d518205b173fc210908235b42ddace590e6b7e5

js/xpconnect/loader/moz.build

@@ -9,6 +9,7 @@ UNIFIED_SOURCES += [
     'ChromeScriptLoader.cpp',
     'mozJSLoaderUtils.cpp',
     'mozJSSubScriptLoader.cpp',
+    'nsImportModule.cpp',
     'ScriptCacheActors.cpp',
     'ScriptPreloader.cpp',
     'URLPreloader.cpp',
@@ -17,13 +18,17 @@ UNIFIED_SOURCES += [
 # mozJSComponentLoader.cpp cannot be built in unified mode because it uses
 # windows.h
 SOURCES += [
-    'mozJSComponentLoader.cpp'
+    'mozJSComponentLoader.cpp',
 ]
 
 IPDL_SOURCES += [
     'PScriptCache.ipdl',
 ]
 
+EXPORTS += [
+    'nsImportModule.h'
+]
+
 EXPORTS.mozilla += [
     'AutoMemMap.h',
     'ScriptPreloader.h',

js/xpconnect/loader/nsImportModule.cpp

@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsImportModule.h"
+
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozJSComponentLoader.h"
+#include "xpcpublic.h"
+#include "xpcprivate.h"
+
+using mozilla::dom::AutoJSAPI;
+
+namespace mozilla {
+namespace loader {
+
+nsresult ImportModule(const char* aURI, const nsIID& aIID, void** aResult) {
+  AutoJSAPI jsapi;
+  MOZ_ALWAYS_TRUE(jsapi.Init(xpc::PrivilegedJunkScope()));
+  JSContext* cx = jsapi.cx();
+
+  JS::RootedObject global(cx);
+  JS::RootedObject exports(cx);
+  MOZ_TRY(mozJSComponentLoader::Get()->Import(cx, nsDependentCString(aURI),
+                                              &global, &exports));
+
+  return nsXPConnect::XPConnect()->WrapJS(cx, exports, aIID, aResult);
+}
+
+}  // namespace loader
+}  // namespace mozilla

js/xpconnect/loader/nsImportModule.h

@@ -0,0 +1,77 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsImportModule_h
+#define nsImportModule_h
+
+#include "mozilla/Attributes.h"
+
+#include "nsCOMPtr.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+namespace loader {
+
+nsresult ImportModule(const char* aURI, const nsIID& aIID, void** aResult);
+
+}  // namespace loader
+}  // namespace mozilla
+
+class MOZ_STACK_CLASS nsImportModule final : public nsCOMPtr_helper {
+ public:
+  nsImportModule(const char* aURI, nsresult* aErrorPtr)
+      : mURI(aURI), mErrorPtr(aErrorPtr) {}
+
+  virtual nsresult NS_FASTCALL operator()(const nsIID& aIID,
+                                          void** aResult) const override {
+    nsresult rv = ::mozilla::loader::ImportModule(mURI, aIID, aResult);
+    if (mErrorPtr) {
+      *mErrorPtr = rv;
+    }
+    return rv;
+  }
+
+ private:
+  const char* mURI;
+  nsresult* mErrorPtr;
+};
+
+/**
+ * These helpers make it considerably easier for C++ code to import a JS module
+ * and wrap it in an appropriately-defined XPIDL interface for its exports.
+ * Typical usage is something like:
+ *
+ * Foo.jsm:
+ *
+ *   var EXPORTED_SYMBOLS = ["foo"];
+ *
+ *   function foo(bar) {
+ *     return bar.toString();
+ *   }
+ *
+ * mozIFoo.idl:
+ *
+ *   interface mozIFoo : nsISupports {
+ *     AString foo(double meh);
+ *   }
+ *
+ * Thing.cpp:
+ *
+ *   nsCOMPtr<mozIFoo> foo = do_ImportModule(
+ *     "resource://meh/Foo.jsm");
+ *
+ *   MOZ_TRY(foo->Foo(42));
+ */
+
+inline nsImportModule do_ImportModule(const char* aURI) {
+  return {aURI, nullptr};
+}
+
+inline nsImportModule do_ImportModule(const char* aURI, nsresult* aRv) {
+  return {aURI, aRv};
+}
+
+#endif  // defined nsImportModule_h