CMake: fix crash on project close during active file system scanning

TreeScanner uses callbacks that can refers to the destroyed objectes
when project closing.

Found scenario:
1. Open big CMake-based project (CLang/LLVM good choose).
2. Until file system scanning finished switch to another session.

Change-Id: Ia0f55f38aea6a9d07ca81aee6c9e9c5662d74f3a
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/cmakeprojectmanager/cmakeproject.cpp

@@ -128,6 +128,11 @@ CMakeProject::CMakeProject(CMakeManager *manager, const FileName &fileName)
 
 CMakeProject::~CMakeProject()
 {
+    if (!m_treeScanner.isFinished()) {
+        auto future = m_treeScanner.future();
+        future.cancel();
+        future.waitForFinished();
+    }
     setRootProjectNode(nullptr);
     m_codeModelFuture.cancel();
     qDeleteAll(m_extraCompilers);

src/plugins/cmakeprojectmanager/treescanner.cpp

@@ -50,6 +50,14 @@ TreeScanner::TreeScanner(QObject *parent) : QObject(parent)
     connect(&m_futureWatcher, &FutureWatcher::finished, this, &TreeScanner::finished);
 }
 
+TreeScanner::~TreeScanner()
+{
+    if (!m_futureWatcher.isFinished()) {
+        m_futureWatcher.cancel();
+        m_futureWatcher.waitForFinished();
+    }
+}
+
 bool TreeScanner::asyncScanForFiles(const Utils::FileName &directory)
 {
     if (!m_futureWatcher.isFinished())

src/plugins/cmakeprojectmanager/treescanner.h

@@ -53,6 +53,7 @@ public:
     using FileTypeFactory = std::function<ProjectExplorer::FileType(const Utils::MimeType &, const Utils::FileName &)>;
 
     explicit TreeScanner(QObject *parent = nullptr);
+    ~TreeScanner();
 
     // Start scanning in given directory
     bool asyncScanForFiles(const Utils::FileName& directory);