wrong-type-argument window-live-p nil occurs at each debugger step triggered by UI buttons

[jsobiecki]

Debugging in dap-mode has stopped working recently. The issue occurs when attempting to step through code after hitting a breakpoint. This happens for both Python and PHP scripts. The error message I get is: wrong-type-argument window-live-p nil

If I repeat to click on step in button, I see that debugger executes next steps, but each step causes same error.
What is suprising, that dap-next command (M-x dap-next) works as expected, this doesn't generate error.

Emacs version: GNU Emacs 29.4 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo version 1.16.0)
dap-mode version: 20250131.1624

dap-mode configuration:

(use-package dap-mode
  :ensure t
  :defer t
  :custom
  (dap-auto-configure-features '(sessions locals controls tooltip)) ;; Customize features
  :config
  (require 'dap-php)   ;; Example: Load Node.js support

  ;; Enable dap-mode and UI mode

  ;; Python
  (require 'dap-python) ;; Example: Load Python support
  (setq dap-python-debugger 'debugpy)
  (dap-auto-configure-mode)
  )

Debug-on-error output

Debugger entered--Lisp error: (wrong-type-argument window-live-p nil)
  #<subr select-window>(nil nil)
  apply(#<subr select-window> (nil nil))
  select-window(nil nil)
  dap--go-to-stack-frame(#s(dap--debug-session :name "Python :: Run file from project directory" :last-id 23 :proc #<process Python :: Run file from project directory> :response-handlers #<hash-table eql 2/65 0x16fc45807fdf> :parser #s(dap--parser :waiting-for-response nil :response-result nil :headers nil :body nil :reading-body nil :body-length nil :body-received nil :leftovers "") :output-buffer #<buffer *Python :: Run file from project directory out*> :thread-id 1 :workspace nil :threads (#<hash-table equal 2/65 0x16fc457e7589>) :thread-states #<hash-table eql 1/65 0x16fc4580819d> :active-frame-id nil :active-frame #<hash-table equal 5/65 0x16fc459529e9> :cursor-marker nil :state running :breakpoints #<hash-table equal 9/65 0x16fc458081bd> :thread-stack-frames #<hash-table eql 1/65 0x16fc458081dd> :launch-args (:name "Python :: Run file from project directory" :type "python" :cwd "/home/garage/ifirma-outda..." :request "launch" :program "/home/garage/ifirma-outda..." :args [] :dap-server-path ("/usr/bin/python" "-m" "debugpy.adapter")) :local-to-remote-path-fn #f(compiled-function (&rest args2) #<bytecode -0xae292674789663f>) :remote-to-local-path-fn #f(compiled-function (&rest args2) #<bytecode -0xae2926747c6263f>) :current-capabilities #<hash-table equal 20/65 0x16fc458089cd> :error-message nil :loaded-sources nil :program-proc nil :metadata #<hash-table eql 0/65 0x16fc45808dd3> :output-displayed nil) #<hash-table equal 5/65 0x16fc459529e9>)
  #f(compiled-function (input0) #<bytecode 0x10819cba8330dc81>)(#<hash-table equal 6/65 0x16fc4595258d>)
  #f(compiled-function (input0) #<bytecode -0x17734ece663602d0>)(#<hash-table equal 6/65 0x16fc4595258d>)
  #f(compiled-function (m) #<bytecode 0x1c0d8016443606e8>)("{\"seq\": 35, \"type\": \"response\", \"request_seq\": 23,...")
  mapc(#f(compiled-function (m) #<bytecode 0x1c0d8016443606e8>) ("{\"seq\": 35, \"type\": \"response\", \"request_seq\": 23,..."))
  #f(compiled-function (_ msg) #<bytecode 0x1d7372552b590d5f>)(#<process Python :: Run file from project directory> "Content-Length: 304\15\n\15\n{\"seq\": 35, \"type\": \"respon...")

[hknox]

I am having the same issue. If it helps, after invoking 'dap-debug', the Message buffer shows:
No message handler for debugpySockets [4 times]
No message handler for process
No message handler for module [2 times]
error in process filter: Wrong type argument: window-live-p, nil [2 times]

Is there some missing configuration piece for debugpy?

[ryanobjc]

I am also seeing this, I am using remote dlv debugging for go. When the code hits a breakpoint I get the filter message, and then nothing happens in the UI. I can see that the thread/goroutine has halted, but any further debugging just doesn't really seem to work well due to the failure in the filter.

[ryanobjc]

Using the debugger, this seems to be the culprit line in dap--go-to-stack-frame:

            (select-window (get-mru-window (selected-frame) nil))

This is on emacs 29.4, built for aarch64-apple-darwin23.4.0

I reproduced this on emacs 30.1, specifically commit 8ac894e
I am using the head of lsp-mode, dap-mode and its dependents (via straight.el package manager)

This is very unfortunate since this makes the entire debugger just... not work at all.

[ryanobjc]

See #837 for a proposed fix.

[marcie1000]

I had the same issue, tried your solution and now it's working.