3

My Emacs version is 24.5.1.

Comint-mode protects the prompt by somehow defining the beginning of line to start directly after the prompt regex. This works for normal motion commands like move-beginning-of-line and even evil-mode motions. For example I can kill the current input by calling evil-change-whole-line and leave the prompt on the same line intact.

Eshell-mode isn't derived from comint mode, and the C-a shortcut is overriden to eshell-bol, which takes the prompt into consideration. So by using normal Emacs shortcuts most things work, but trying to use the standard commands for movement like move-beginning-of-line yields unexpected results. So by using evil-change-whole-line I kill the whole line, when I only wanted to kill the input.

How does comint-mode protect the prompt and is it possible to implement the same behavior in eshell-mode?

Things I have tried but didn't bear fruit:

  1. comint-line-beginning-position and comint-bolare defined in comint.el, but they aren't called when calling evil-change-whole-line or move-beginning-of-line.
  2. I noticed some references to the inhibit-field-text-motion variable in comint.el. But it is nil in at least shell-mode, which is comint-derived.
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Dan's comment helped me on the way. Comint achieves the prompt protecting functionality with text-properties. I can add the needed properties in eshell by evaluating.

(add-text-properties (point-at-bol)
                     (point)
                     '(inhibit-line-move-field-capture t
                       rear-nonsticky t
                       field output
                       front-sticky (field inhibit-line-move-field-capture)))

I'm still unsure how this specific combination of properties result in the functionality. But I was satisfied and added these properties to my custom prompt with propertize

  • "how [these] ... specific properties result in the functionality" - field and the "sticky" properties are explained in the linked manual page. inhibit-line-move-field-capture is not documented, but appears to be checked by line-move-1 and line-move-finish in simple.el. – npostavs Jul 1 '15 at 20:53
  • Thanks @npostavs for pointing me to simple.el! At least line-move-1 is called for most of the evil-mode movement commands. It's a shame the inhibit-line-move-field-capture property isn't documented thoroughly, because those functions are quite complex. I hope I have the time to study this further so I can propose a patch for eshell. – Martin Yrjölä Jul 2 '15 at 6:02

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