Allow plugins to insert custom imports.

This patch allows a plugin to insert custom imports. These imports are
used by QtC for syntax highlighting and code completion. This way a
plugin can register types and objects that are available only at
runtime.

This is an example of an imports function implementation:

QList<Import> MyPlugin::imports(ValueOwner *valueOwner, const Document
*context) const
{
  // context is needed to know from which project is the opened document
  // in this example we don't care about multiple projects

  Import import;
  import.object = new QmlJS::ObjectValue(valueOwner, "<defaults>");
  import.valid = true;
  const ComponentVersion version(1, 0);
  import.info = ImportInfo::moduleImport("MyPlugin", version,
QString());
  auto myType = valueOwner->newObject(nullptr)
  myType->setMember("myProperty", valueOwner->valueOwner->intValue());
  // add more properties & methods/signals to myType

  import.object->setMember("MyType", myType);

  // in this example we return only one, but you care return more than
one
  return QList<Import>(import);
}

Change-Id: I395c273c7b15a9e4ed5a89a81d70ff92db2b7c0c
Reviewed-by: Marco Benelli <marco.benelli@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>

src/libs/qmljs/qmljslink.cpp

@@ -38,6 +38,8 @@
 #include "qmljsqrcparser.h"
 #include "qmljsconstants.h"
 
+#include <extensionsystem/pluginmanager.h>
+
 #include <QDir>
 
 using namespace LanguageUtils;
@@ -213,6 +215,13 @@ Context::ImportsPerDocument LinkPrivate::linkImports()
     if (document) {
         // do it on document first, to make sure import errors are shown
         Imports *imports = new Imports(valueOwner);
+
+        // Add custom imports for the opened document
+        auto providers = ExtensionSystem::PluginManager::getObjects<CustomImportsProvider>();
+        foreach (const auto &provider, providers)
+            foreach (const auto &import, provider->imports(valueOwner, document.data()))
+                importCache.insert(ImportCacheKey(import.info), import);
+
         populateImportedTypes(imports, document);
         importsPerDocument.insert(document.data(), QSharedPointer<Imports>(imports));
     }