When iTerm2 is terminating, detach from tmux gateways before windows are closed. Issue 4926

sources/PTYSession.m

@@ -456,6 +456,14 @@ static const NSTimeInterval kBackgroundUpdateCadence = 1;
                                                  selector:@selector(profileSessionNameDidEndEditing:)
                                                      name:kProfileSessionNameDidEndEditing
                                                    object:nil];
+        // Detach before windows get closed. That's why we have to use the
+        // iTermApplicationWillTerminate notification instead of
+        // NSApplicationWillTerminate, since this gets run before the windows
+        // are released.
+        [[NSNotificationCenter defaultCenter] addObserver:self
+                                                 selector:@selector(applicationWillTerminate:)
+                                                     name:iTermApplicationWillTerminate
+                                                   object:nil];
         [self updateVariables];
     }
     return self;
@@ -3641,6 +3649,11 @@ ITERM_WEAKLY_REFERENCEABLE
     [self sanityCheck];
 }
+- (void)applicationWillTerminate:(NSNotification *)notification {
+    // See comment where we observe this notification for why this is done.
+    [self tmuxDetach];
+}
+
 - (void)synchronizeTmuxFonts:(NSNotification *)notification
 {
     if (!_exited && [self isTmuxClient]) {
@@ -4123,18 +4136,15 @@ ITERM_WEAKLY_REFERENCEABLE
     }
 }
-- (BOOL)isTmuxClient
-{
+- (BOOL)isTmuxClient {
     return self.tmuxMode == TMUX_CLIENT;
 }
-- (BOOL)isTmuxGateway
-{
+- (BOOL)isTmuxGateway {
     return self.tmuxMode == TMUX_GATEWAY;
 }
-- (void)tmuxDetach
-{
+- (void)tmuxDetach {
     if (self.tmuxMode != TMUX_GATEWAY) {
         return;
     }

sources/iTermApplicationDelegate.h

@@ -40,6 +40,7 @@ extern NSString *const kNonTerminalWindowBecameKeyNotification;
 extern NSString *const kMarkAlertActionModalAlert;
 extern NSString *const kMarkAlertActionPostNotification;
 extern NSString *const kShowFullscreenTabsSettingDidChange;
+extern NSString *const iTermApplicationWillTerminate;
 int DebugLogImpl(const char *file, int line, const char *function, NSString* value);

sources/iTermApplicationDelegate.m

@@ -91,6 +91,7 @@ static NSString *const kHotkeyWindowRestorableState = @"kHotkeyWindowRestorableS
 static NSString *const kHaveWarnedAboutIncompatibleSoftware = @"NoSyncHaveWarnedAboutIncompatibleSoftware";
 static NSString *const kRestoreDefaultWindowArrangementShortcut = @"R";
+NSString *const iTermApplicationWillTerminate = @"iTermApplicationWillTerminate";
 static BOOL gStartupActivitiesPerformed = NO;
 // Prior to 8/7/11, there was only one window arrangement, always called Default.
@@ -593,6 +594,9 @@ static BOOL hasBecomeActive = NO;
         [[iTermController sharedInstance] killRestorableSessions];
     }
+    // Last chance before windows get closed.
+    [[NSNotificationCenter defaultCenter] postNotificationName:iTermApplicationWillTerminate object:nil];
+
     // This causes all windows to be closed and all sessions to be terminated.
     [iTermController releaseSharedInstance];