fix: fixes error when a utility frame is the current frame

On Mac OS X, small frames that don't allow user focus may be selected
when the process filter is processed.  By walking up the parent-frame
list, we can get to the frame that the user is actually able to use,
and thus the call to (get-mru-window) does not return nil and the
whole process filter aborts.

Should fix bug #828

Author: ryanobjc

dap-mode.el

@@ -784,7 +784,7 @@ will be reversed."
   (-when-let* ((source (gethash "source" stack-frame))
                (sourceReference (gethash "sourceReference" source))
                (sourceReferenceKey (format "%s-%s" name sourceReference)))
-    (select-window (get-mru-window (selected-frame) nil))
+    (select-window (get-mru-window (dap--selected-frame) nil))
     (if-let* ((existing-buffer (get-buffer sourceReferenceKey)))
         (switch-to-buffer existing-buffer)
       (dap--send-message
@@ -810,6 +810,15 @@ will be reversed."
                          path)))
       (--> debug-session (dap--debug-session-remote-to-local-path-fn it) (funcall it remote-path)))))
 
+(defun dap--selected-frame ()
+  "Select the 'main' frame when we have a utility/subframe selected"
+  (cl-labels ((helper (f)
+                (let ((parent-frame (frame-parameter f 'parent-frame)))
+                  (if parent-frame
+                      (helper parent-frame)
+                    f))))
+    (helper (selected-frame))))
+
 (defun dap--go-to-stack-frame (debug-session stack-frame)
   "Make STACK-FRAME the active STACK-FRAME of DEBUG-SESSION."
   (when stack-frame
@@ -821,7 +830,7 @@ will be reversed."
       ;; stack trace.
       (if (and path (file-exists-p path))
           (progn
-            (select-window (get-mru-window (selected-frame) nil))
+            (select-window (get-mru-window (dap--selected-frame) nil))
             (find-file path)
             (goto-char (point-min))
             (forward-line (1- line))