how to modify buffer display behaviour?

Question

I use display-buffer-alist to Configure buffer display. For example I have this snippet to display flycheck errors buffer.

(add-to-list 'display-buffer-alist
             `(,(rx bos "*Flycheck errors*" eos)
               (display-buffer-reuse-window
                display-buffer-below-selected)
               (reusable-frames . visible)
               (side            . bottom)
               (window-height   . 0.4)))

This works well, but when I want the same behaviour for the Messages buffer, it doesn't work. Why does this only work for certain buffers ?

And is it also possible to configure the display for buffers, that are opened by specific commands ? One example is shell-mode. When I open a new shell buffer, with another one already existing, my display modifications don't work because the name of the buffer is different.

Answer 1

Citation of my comment:

Did you really try M-x (display-buffer "*Messages*")?? It works for me with your entry in display-buffer-alist and "*flycheck errors*" replaced by "*Messages*"! Could it be that you tried switch-to-buffer instead and expected the same effects as for display-buffer? They behave differently (at least for me).

And @bertfred's answer:

That was the problem. I have a custom function that displays the message buffer. However it works with eshell when I use

(defun switch-to-eshell () (interactive) (switch-to-buffer (eshell)))

eshell generates the buffer and shows it with pop-to-buffer-same-window which in turn calls pop-to-buffer and this calls display-buffer.

There are also occasions when switch-to-buffer calls pop-to-buffer. In that case your entries in display-buffer-alist become relevant. But normally, switch-to-buffer uses just the low-level routine set-buffer where the entries in display-buffer-alist are irrelevant.

Relevant citation from the help of switch-to-buffer:

If the selected window cannot display the specified buffer because it is a minibuffer window or strongly dedicated to another buffer, call ‘pop-to-buffer’ to select the buffer in another window. In interactive use, if the selected window is strongly dedicated to its buffer, the value of the option ‘switch-to-buffer-in-dedicated-window’ specifies how to proceed.

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You also asked:

And is it also possible to configure the display for buffers, that are opened by specific commands ? One example is shell-mode. When I open a new shell buffer, with another one already existing, my display modifications don't work because the name of the buffer is different.

The documentation of generate-new-buffer-name describes how unique buffernames are generated:

generate-new-buffer-name is a built-in function in ‘C source code’.

(generate-new-buffer-name NAME &optional IGNORE)

Return a string that is the name of no existing buffer based on NAME. If there is no live buffer named NAME, then return NAME. Otherwise modify name by appending ‘<NUMBER>’, incrementing NUMBER (starting at 2) until an unused name is found, and then return that name. Optional second argument IGNORE specifies a name that is okay to use (if it is in the sequence to be tried) even if a buffer with that name exists.

If NAME begins with a space (i.e., a buffer that is not normally visible to users), then if buffer NAME already exists a random number is first appended to NAME, to speed up finding a non-existent buffer.

So (rx "SomeBufferName<" (one-or-more digit) ">") should do the job. Just replace SomeBufferName with the name of the first buffer of this special kind.