Filter Helm buffers by mode in ibuffer

Question

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?

Answer 1

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

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

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.