Clang: Use completion through backend process

This makes us independent of libclang crashes for completion.
Re-parsing for highlighting still happens in the Qt Creator process.

Run in verbose mode:
    qtc.clangcodemodel.ipc=true

Run tests:
    -test "ClangCodeModel"

Task-number: QTCREATORBUG-14108
Task-number: QTCREATORBUG-12819
Change-Id: Id3e95bd2afdb6508bbd1d35fddc69534a909b905
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/plugins/clangcodemodel/clangutils.cpp

@@ -36,9 +36,12 @@
 #include <coreplugin/icore.h>
 #include <coreplugin/idocument.h>
 
+#include <cpptools/baseeditordocumentparser.h>
 #include <cpptools/cppprojects.h>
 #include <cpptools/cppworkingcopy.h>
 
+#include <utils/qtcassert.h>
+
 #include <QDir>
 #include <QFile>
 #include <QLoggingCategory>
@@ -202,5 +205,28 @@ QStringList createPCHInclusionOptions(const QString &pchFile)
     return createPCHInclusionOptions(QStringList() << pchFile);
 }
 
+ProjectPart::Ptr projectPartForFile(const QString &filePath)
+{
+    if (CppTools::BaseEditorDocumentParser *parser = CppTools::BaseEditorDocumentParser::get(filePath))
+        return parser->projectPart();
+    return ProjectPart::Ptr();
+}
+
+bool isProjectPartValid(const ProjectPart::Ptr projectPart)
+{
+    if (projectPart)
+        return CppModelManager::instance()->projectPartForProjectFile(projectPart->projectFile);
+    return false;
+}
+
+QString projectFilePathForFile(const QString &filePath)
+{
+    const ProjectPart::Ptr projectPart = projectPartForFile(filePath);
+
+    if (isProjectPartValid(projectPart))
+        return projectPart->projectFile; // OK, Project Part is still loaded
+    return QString();
+}
+
 } // namespace Utils
 } // namespace Clang