Detect qt sub projects and special case their build directory

Check every project's path against the source paths of all existing qts.
If we find a match, make it build in the right place by default.
Works for both in source and shadow builds.

Note: There's a quadratic algorithm since foreach kit we check against
all qt versions. That's unlikely to be a problem and non trivial to
fix.

Change-Id: I9f3456f3e835ee6adc35c26fe5c328c01387a8aa
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/qmakeprojectmanager/qmakeproject.cpp

@@ -57,6 +57,7 @@
 #include <proparser/qmakevfs.h>
 #include <qtsupport/profilereader.h>
 #include <qtsupport/qtkitinformation.h>
+#include <qtsupport/qtversionmanager.h>
 #include <qtsupport/uicodemodelsupport.h>
 #include <resourceeditor/resourcenode.h>
 
@@ -362,6 +363,10 @@ QmakeProject::QmakeProject(QmakeManager *manager, const QString &fileName) :
 
     connect(BuildManager::instance(), SIGNAL(buildQueueFinished(bool)),
             SLOT(buildFinished(bool)));
+
+    setPreferredKitMatcher(KitMatcher([this](const Kit *kit) -> bool {
+                               return matchesKit(kit);
+                           }));
 }
 
 QmakeProject::~QmakeProject()
@@ -1605,6 +1610,21 @@ void QmakeProject::collectLibraryData(const QmakeProFileNode *node, DeploymentDa
     }
 }
 
+bool QmakeProject::matchesKit(const Kit *kit)
+{
+    QList<QtSupport::BaseQtVersion *> parentQts;
+    Utils::FileName filePath = projectFilePath();
+    foreach (QtSupport::BaseQtVersion *version, QtSupport::QtVersionManager::validVersions()) {
+        if (version->isInSourceDirectory(filePath))
+            parentQts.append(version);
+    }
+
+    QtSupport::BaseQtVersion *version = QtSupport::QtKitInformation::qtVersion(kit);
+    if (!parentQts.isEmpty())
+        return parentQts.contains(version);
+    return true;
+}
+
 QString QmakeProject::executableFor(const QmakeProFileNode *node)
 {
     const ProjectExplorer::Kit * const kit = activeTarget()->kit();