[apps/code] Check that app can be exited before switching to DFU

This fixes the following crash: create a script which contains only
"input()". Execute it, then while in the input, plug in the calculator.
When un-plugging it, the device crashes.

apps/apps_container.cpp

@@ -152,14 +152,25 @@ bool AppsContainer::dispatchEvent(Ion::Events::Event event) {
   if (event == Ion::Events::USBEnumeration) {
     if (Ion::USB::isPlugged()) {
       App::Snapshot * activeSnapshot = (activeApp() == nullptr ? appSnapshotAtIndex(0) : activeApp()->snapshot());
-      /* Just after a software update, the battery timer does not have time to
-       * fire before the calculator enters DFU mode. As the DFU mode blocks the
-       * event loop, we update the battery state "manually" here. */
-      updateBatteryState();
-      switchTo(usbConnectedAppSnapshot());
-      Ion::USB::DFU();
-      switchTo(activeSnapshot);
-      didProcessEvent = true;
+      if (activeApp() == nullptr || activeApp()->prepareForExit()) {
+        /* Just after a software update, the battery timer does not have time to
+         * fire before the calculator enters DFU mode. As the DFU mode blocks the
+         * event loop, we update the battery state "manually" here. */
+        updateBatteryState();
+        switchTo(usbConnectedAppSnapshot());
+        Ion::USB::DFU();
+        switchTo(activeSnapshot);
+        didProcessEvent = true;
+      } else {
+        /* activeApp()->prepareForExit() returned false, which means that the
+         * app needs another event loop to prepare for being switched off.
+         * Discard the current enumeration interruption.
+         * The USB host tries a few times in a row to enumerate the device, so
+         * hopefully the device will get another enumeration event soon and this
+         * time the device will be ready to go in DFU mode. Otherwise, the user
+         * needs to re-plug the device to go into DFU mode. */
+        Ion::USB::clearEnumerationInterrupt();
+      }
     } else {
       /* Sometimes, the device gets an ENUMDNE interrupts when being unplugged
        * from a non-USB communicating host (e.g. a USB charger). The interrupt
@@ -212,6 +223,7 @@ bool AppsContainer::processEvent(Ion::Events::Event event) {
 }
 
 void AppsContainer::switchTo(App::Snapshot * snapshot) {
+  assert(activeApp() == nullptr || activeApp()->prepareForExit());
   if (activeApp() && snapshot != activeApp()->snapshot()) {
     resetShiftAlphaStatus();
   }

apps/code/app.cpp

@@ -88,6 +88,7 @@ App::App(Container * container, Snapshot * snapshot) :
 }
 
 App::~App() {
+  assert(!m_consoleController.inputRunLoopActive());
   deinitPython();
 }
 

apps/code/app.h

@@ -37,6 +37,13 @@ public:
     ScriptStore m_scriptStore;
   };
   ~App();
+  bool prepareForExit() override {
+    if (m_consoleController.inputRunLoopActive()) {
+      m_consoleController.terminateInputLoop();
+      return false;
+    }
+    return true;
+  }
   StackViewController * stackViewController() { return &m_codeStackViewController; }
   ConsoleController * consoleController() { return &m_consoleController; }
 

escher/include/escher/app.h

@@ -50,6 +50,9 @@ public:
   void setFirstResponder(Responder * responder);
   Responder * firstResponder();
   virtual bool processEvent(Ion::Events::Event event);
+  /* prepareForExit returns true if the app can be switched off in the current
+   * runloop step, else it prepares for a switch off and returns false. */
+  virtual bool prepareForExit() { return true; }
   void displayModalViewController(ViewController * vc, float verticalAlignment, float horizontalAlignment,
     KDCoordinate topMargin = 0, KDCoordinate leftMargin = 0, KDCoordinate bottomMargin = 0, KDCoordinate rightMargin = 0);
   void dismissModalViewController();