add: a text property for display string in the right margin

[AmaiKinono]

See #14

The right margin text is displayed in the same line:

or in a new line, when the space is not enough:

[raxod502]

The feature is fine, but text display based on window width calculations is too flaky (what happens if you resize the window during a session?). A better approach is to use a text overlay, as in radian-software/ctrlf#32 (comment).

[AmaiKinono]

I failed to figure it out. The code I gave in radian-software/ctrlf#32 (comment) displays a very wide space, and from the manual, seems that's its only usage. I didn't find other display property of overlay that allows right aligning text.

Could you explain a bit more about how this should be done?

[raxod502]

Sorry, didn't realize that example was not an appropriate one. It is in fact possible, though: lsp-ui does this to display its in-buffer error messages. Here's the code:

https://github.com/emacs-lsp/lsp-ui/blob/bf3966e87c91c5d825c483ce0883f30dd2272b62/lsp-ui-sideline.el#L257-L259

It uses a "pixel specification" in the :align-to property. This allows the alignment to be recomputed on every redisplay, solving the window resizing problem.

Here's what the overlays look like in that package:

[AmaiKinono]

Thanks for the example, the trick is neat :D

Please see if this can be merged.

[raxod502]

• looks good
• some minor suggestions
• can you suggest a code snippet that demonstrates the functionality so I can test it?
• we should have an entry in the CHANGELOG

Thank you for the help!

[AmaiKinono]

an entry in the CHANGELOG

Done.

can you suggest a code snippet that demonstrates the functionality so I can test it?

This is a simple test:

(completing-read
 "Hi: "
 (list
  (propertize "item1"
              'selectrum-candidate-display-right-margin "annotation1"
              'selectrum-candidate-display-prefix "prefix1 ")
  (propertize "item2"
              'selectrum-candidate-display-right-margin "annotation2"
              'selectrum-candidate-display-prefix "prefix2 ")))

And this is a command I want to implement using this feature:

(defun insert-unicode-char (&optional count)
  (interactive "p")
  (let ((selectrum-preprocess-candidates-function
         (lambda (collection)
           (selectrum--map-destructive
            (lambda (name)
              (let ((code (char-from-name name)))
                (propertize
                 name
                 'selectrum-candidate-full
                 (format "%c" code name code)
                 'selectrum-candidate-display-prefix
                 (format "%06X " code)
                 'selectrum-candidate-display-right-margin
                 (format "%c" code))))
            collection))))
    (call-interactively #'insert-char)))