transient-display-buffer-action bug when using non-side-window specification

[karthink]

I've been dealing with two display-buffer issues with transient when transient-display-buffer-action is set to some value that doesn't use a side window. One issue is new (transient 0.8.3+) and one is old (since at least 2021).

The following examples are produced via emacs -q with transient and magit installed.

Elpaca test environment for reproducing bug

(elpaca-test
  :name "transient"
  :dir "/tmp/transient-test"
  :interactive t
  :early-init
  (setq package-enable-at-startup nil
        package-quickstart nil
        load-prefer-newer t)
  :init
  (elpaca transient)
  (elpaca gptel)
  (elpaca magit)
  (setq transient-display-buffer-action
        '(display-buffer-below-selected))
  
  (tool-bar-mode 0))

M-x magit-version:

Magit v4.3.0-21-g4a01405, Transient 0.8.4, Forge 0.4.7, Git 2.47.2, Emacs 29.4, gnu/linux

(But this problem is independent of magit, see below)

Issue 1: Reading from minibuffer in a transient causes extra windows to appear (transient 0.8.3+)

screencast_20250215T220929.mp4

To reproduce:

(setq transient-display-buffer-action '((display-buffer-below-selected))
      transient-show-during-minibuffer-read nil)

or

(setq transient-display-buffer-action '(display-buffer-below-selected)
      transient-show-during-minibuffer-read nil)

Then set a transient option whose reader uses the minibuffer.

Result: An extra window is spawned that has to be cleared manually after exiting the transient.

This happens with all transients, see gptel#583 for another example.

Issue 2: Bringing up help/a man page from transient causes extra window to appear (transient 0.4.0+)

screencast_20250215T221142.mp4

The settings are the same as above, but transient-show-during-minibuffer-read is irrelevant.

To reproduce, bring up the man page for an option (in this case, c C-h c for magit-commit). Dismissing the man page leaves an extra window open.

[tarsius]

Use this instead:

(setq transient-display-buffer-action
      '(display-buffer-below-selected
        (dedicated . t)
        (inhibit-same-window . t)))

I've updated (04dab99) the documentation to make it explicit that these alist entries shouldn't be dropped.

[karthink]

Thanks @tarsius

[karthink]

@tarsius There appears to be more to the story. With

• transient-display-buffer-action set to the default value
• transient-show-during-minibuffer-read set to the default value (nil)
• helm-mode active,

I tried running the r infix action in this transient:

(transient-define-prefix test-read ()
  "TODO"
  ["Test"
   ("r" "read" "r"
    :class transient-option
    :prompt "Pick: "
    :reader (lambda (p i h)
	      (completing-read p '("one" "two" "three")
			       nil nil i h)))])

The result after running r, picking a value and quitting the transient with C-g was the same bug as in my opening post, an extra window sticks around.

helm-mode used a window + regular buffer to read the completing-read value, so I'm guessing that's part of the problem. I'm not familiar with Helm so I don't know if it's because Helm ignores the display-buffer action alists. This testing is on behalf of (another) user who complained about this issue with gptel + Helm + the latest Transient, at gptel#656.

[tarsius]

3cd02ec should help.

[daedsidog]

@tarsius It did not. The gptel bug still occurs even with that change.
Apologies if the discussion is unrelated.

[karthink]

Does it still occur with the test-read transient from above too?

[daedsidog]

@karthink Yes:

Note that it doesn't happen if I use version 0.7.5 (transient-20240918.1138, it's just the version I had on my old computer) of Transient. Gptel also works fine in that version.

[tarsius]

Continues at #361.