Clang: Hook up supportive translation unit on first edit

Parsing happens rotationally on the translation units.

The recently parsed translation unit is used for completion jobs while
the older version is used for parse jobs.

Advantages:
  A1. A completion job cannot be blocked anymore by currently running
      parse job.
  A2. Faster triggering of parse jobs. A reparse was triggered about
      1650ms after the last keystroke. This is down to 500ms now since we
      do not have a blocking translation unit for the completion anymore.

Disadvantages:
  D1. Memory consumption is doubled for an edited document.
      This could be addressed by suspending the second translation unit
      after some time of inactivity.
  D2. Setup of the supportive translation unit takes some time.

Change-Id: I958c883c01f274530f5482c788c15cd38d6f4c3e
Reviewed-by: David Schulz <david.schulz@qt.io>

src/tools/clangbackend/ipcsource/clangsupportivetranslationunitinitializer.cpp

@@ -0,0 +1,141 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "clangsupportivetranslationunitinitializer.h"
+
+#include "clangjobs.h"
+#include "clangtranslationunits.h"
+
+#include <utils/qtcassert.h>
+
+namespace ClangBackEnd {
+
+    // TODO: Check translation unit id?
+
+SupportiveTranslationUnitInitializer::SupportiveTranslationUnitInitializer(
+        const Document &document,
+        Jobs &jobs)
+    : m_document(document)
+    , m_jobs(jobs)
+{
+}
+
+void SupportiveTranslationUnitInitializer::setJobRequestCreator(const JobRequestCreator &creator)
+{
+    m_jobRequestCreator = creator;
+}
+
+void SupportiveTranslationUnitInitializer::setIsDocumentClosedChecker(
+        const IsDocumentClosedChecker &isDocumentClosedChecker)
+{
+    m_isDocumentClosedChecker = isDocumentClosedChecker;
+}
+
+SupportiveTranslationUnitInitializer::State SupportiveTranslationUnitInitializer::state() const
+{
+    return m_state;
+}
+
+void SupportiveTranslationUnitInitializer::startInitializing()
+{
+    QTC_CHECK(m_state == State::NotInitialized);
+    if (abortIfDocumentIsClosed())
+        return;
+
+    m_document.translationUnits().createAndAppend();
+
+    m_jobs.setJobFinishedCallback([this](const Jobs::RunningJob &runningJob) {
+        checkIfParseJobFinished(runningJob);
+    });
+    addJob(JobRequest::Type::ParseSupportiveTranslationUnit);
+    m_jobs.process();
+
+    m_state = State::WaitingForParseJob;
+}
+
+void SupportiveTranslationUnitInitializer::checkIfParseJobFinished(const Jobs::RunningJob &job)
+{
+    QTC_CHECK(m_state == State::WaitingForParseJob);
+    if (abortIfDocumentIsClosed())
+        return;
+
+    if (job.jobRequest.type == JobRequest::Type::ParseSupportiveTranslationUnit) {
+        m_jobs.setJobFinishedCallback([this](const Jobs::RunningJob &runningJob) {
+            checkIfReparseJobFinished(runningJob);
+        });
+
+        addJob(JobRequest::Type::ReparseSupportiveTranslationUnit);
+
+        m_state = State::WaitingForReparseJob;
+    }
+}
+
+void SupportiveTranslationUnitInitializer::checkIfReparseJobFinished(const Jobs::RunningJob &job)
+{
+    QTC_CHECK(m_state == State::WaitingForReparseJob);
+    if (abortIfDocumentIsClosed())
+        return;
+
+    if (job.jobRequest.type == JobRequest::Type::ReparseSupportiveTranslationUnit) {
+        if (m_document.translationUnits().areAllTranslationUnitsParsed()) {
+            m_jobs.setJobFinishedCallback(nullptr);
+            m_state = State::Initialized;
+        } else {
+            // The supportive translation unit was reparsed, but the document
+            // revision changed in the meanwhile, so try again.
+            addJob(JobRequest::Type::ReparseSupportiveTranslationUnit);
+        }
+    }
+}
+
+bool SupportiveTranslationUnitInitializer::abortIfDocumentIsClosed()
+{
+    QTC_CHECK(m_isDocumentClosedChecker);
+
+    if (m_isDocumentClosedChecker(m_document.filePath(), m_document.projectPartId())) {
+        m_state = State::Aborted;
+        return true;
+    }
+
+    return false;
+}
+
+void SupportiveTranslationUnitInitializer::addJob(JobRequest::Type jobRequestType)
+{
+    QTC_CHECK(m_jobRequestCreator);
+
+    const JobRequest jobRequest = m_jobRequestCreator(m_document,
+                                                      jobRequestType,
+                                                      PreferredTranslationUnit::LastUninitialized);
+
+    m_jobs.add(jobRequest);
+}
+
+void SupportiveTranslationUnitInitializer::setState(const State &state)
+{
+    m_state = state;
+}
+
+} // namespace ClangBackEnd