macOS: detect and warn if running translocated

Translocation forces us to rebuild the nav-cache each launch, and might
mess up some other details, so let’s warn the user they should copy
the app to Applications or similar.

src/GUI/CocoaHelpers.h

@@ -46,4 +46,12 @@ void transformToForegroundApp();
  */
 void cocoaRegisterTerminateHandler();
 
+/**
+ * @brief helper to detect if we're running translocated or not.
+ * Google 'Gatekeep app translation' for more info about this; basically it
+ * happens when the user runs us directly from the DMG, and this makes
+ * for very nasty file paths.
+ */
+bool cocoaIsRunningTranslocated();
+
 #endif // of FG_GUI_COCOA_HELPERS_H

src/GUI/CocoaHelpers.mm

@@ -24,6 +24,7 @@
 
 // standard
 #include <string>
+#include <dlfcn.h>
 
 // OS
 
@@ -264,3 +265,30 @@ void cocoaRegisterTerminateHandler()
 }
 
 
+
+bool cocoaIsRunningTranslocated()
+{
+    // #define NSAppKitVersionNumber10_11 1404
+    if (floor(NSAppKitVersionNumber) <= 1404) {
+        return false;
+    }
+
+    void *handle = dlopen("/System/Library/Frameworks/Security.framework/Security", RTLD_LAZY);
+    if (handle == NULL) {
+        return false;
+    }
+
+    bool isTranslocated = false;
+    using SecIsTranslocatedFunc = Boolean (*)(CFURLRef path, bool *isTranslocated, CFErrorRef * __nullable error);
+
+    SecIsTranslocatedFunc f = reinterpret_cast<SecIsTranslocatedFunc>(dlsym(handle, "SecTranslocateIsTranslocatedURL"));
+    if (f != NULL) {
+        auto url = CFBundleCopyBundleURL(CFBundleGetMainBundle());
+        f(url, &isTranslocated, NULL);
+
+        CFRelease(url);
+    }
+
+    dlclose(handle);
+    return isTranslocated;
+}

src/GUI/QtLauncher.cxx

@@ -76,6 +76,10 @@
 #include "PathListModel.hxx"
 #include "UnitsModel.hxx"
 
+#if defined(SG_MAC)
+#include <GUI/CocoaHelpers.h>
+#endif
+
 using namespace flightgear;
 using namespace simgear::pkg;
 using std::string;
@@ -366,6 +370,20 @@ void initApp(int& argc, char** argv, bool doInitQSettings)
         // http://doc.qt.io/qt-5/qcoreapplication.html#details
         ::setlocale(LC_NUMERIC, "C");
         ::setlocale(LC_COLLATE, "C");
+
+
+#if defined(SG_MAC)
+        if (cocoaIsRunningTranslocated()) {
+            addSentryBreadcrumb("did show translocation warning", "info");
+            const char* titleKey = QT_TRANSLATE_NOOP("macTranslationWarning", "Application running from download location");
+            const char* key = QT_TRANSLATE_NOOP("macTranslationWarning", "FlightGear is running from the download image. For better performance and to avoid potential problems, "
+                                                "please copy FlightGear to some other location, such as your desktop or Applications folder.");
+            QString msg = qApp->translate("macTranslationWarning", key);
+            QString title = qApp->translate("macTranslationWarning", titleKey);
+
+            QMessageBox::warning(nullptr, title, msg);
+        }
+#endif
     }
 
     if (doInitQSettings) {