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When I try to filter buffers by mode in ibuffer, I am not able to filter by major mode helm-mode. For example,

 MR Name                 Size Mode
 -- ----                 ---- ----
 *  *helm apropos*        117 Helm             
 *  *helm projectile*    3633 Helm             
 *  *helm-package*        187 Helm             

these three buffers say "Helm" in the mode column, but will only match fundamental-mode when filtering on major mode or derived mode. Is this a bug?

6

It is not a bug. helm.el does not provide any major mode for helm buffers. So they are infact in fundamental-mode. However it does set the variable mode-name to Helm which is what you are seeing in the mode column. The mode-name variable is a buffer local variable that can contain a user friendly name for the buffer's major-mode and is/can be different from major-mode.

Check out the defun helm-create-helm-buffer for more details.

Note that ibuffer lets you mark all helm buffers by marking by mode regexp % m followed by Helm at the prompt. The usual * M does not work though. If you want to create filter groups for helm, you can use the ibuffer-filter-by-predicate mapped to / e and entering the following at the prompt.

(string-match "Helm" mode-name)

For instance, here is a working example of a saved filter group

enter image description here

and here is the resulting ibuffer window after ibuffer-switch-to-saved-filter-groups.

enter image description here

I can only guess why Helm does not have a dedicated major mode. Unlike buffers with major modes

  • helm completion buffers are always disposable,
  • do not need any special syntax map,
  • font-lock is dependent upon the command invoked
  • most importantly, keymap is active only for the active helm buffer

So there is no special reason for these buffers to have a dedicated major-mode. You can ask the maintainer for his reasons though. Maybe, the overhead of having a major-mode is not worth the trivial advantages it brings.

  • Unfortunately buffer marking functions do not allow me to create custom filter groups. – nispio Oct 15 '14 at 13:12
  • 1
    Okay, I see what you are saying. So why is Helm changing mode-name without changing the mode? Why not create an inherited mode from fundamental mode and invoke it from helm-create-helm-buffer? Would there be some disadvantage to creating a helm mode vs faking it by overwriting mode-name? – nispio Oct 15 '14 at 13:15
  • Regarding why there is no dedicated major mode, I can only guess the intentions of the maintainer. There is nothing to be gained by defining a new major mode for helm completion buffers which are disposable. Mode-name is just the lighter for the modeline. For instance the scratch buffer has a major mode of lisp-interaction-mode while its mode-name is Lisp Interaction. mode-name is visible to the user, so a friendly string is often used. – Vamsi Oct 15 '14 at 15:43
  • @nispio I have edited the answer to show how you can filter helm buffers as well. – Vamsi Oct 15 '14 at 16:59

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