filling in the minibuffer

[Alex Schroeder]

I sometimes have the need for filling a paragraph in the minibuffer.

(let ((debug-ignored-errors nil)
      (debug-on-error t))
  (read-from-minibuffer "Text: "))

Type a few words, hit M-q.

You get an error:

fill-delete-newlines: Text is read-only

When you type a few words, C-q C-j to insert a newline, and type some
more, and then hit M-q, filling works as expected.

I think we should try to make it work without a newline in the
minibuffer, too.  In fact, I think this used to work in earlier
versions.

Why does it happen?

The prompt ends with a space.  When fill-delete-newlines gets called, 
we have a problem at the very end:

  (if (and nosqueeze (not (eq justify 'full)))
      nil
    (canonically-space-region (or squeeze-after (point)) to)
    ;; Remove trailing whitespace.
    ;; Maybe canonically-space-region should do that.
    (goto-char to) (delete-char (- (skip-chars-backward " \t"))))
  (goto-char from))

That is, this tries to delete the space ending the prompt, which
fails.

What should we do?  Should we just skip over read-only text when
filling?

Maybe that is not the whole story, because why is the code being
called on the prompt only?

Edebugging fill-paragraph I note the following:

        (save-excursion
          ;; To make sure the return value of forward-paragraph is meaningful,
          ;; we have to start from the beginning of line, otherwise skipping
          ;; past the last few chars of a paragraph-separator would count as
          ;; a paragraph (and not skipping any chars at EOB would not count
          ;; as a paragraph even if it is).
          (move-to-left-margin)
          (if (not (zerop (forward-paragraph)))
              ;; There's no paragraph at or after point: give up.
              (setq fill-pfx "")
            (let ((end (point))
                  (beg (progn (backward-paragraph) (point))))
              (goto-char before)

The call to move-to-left-margin takes us to the beginning of the
prompt.  The forward-paragraph takes us to end of the prompt (end).
Then the next backward-paragraph takes us to the beginning of the
prompt again (beg).  I think this is the bug.

Maybe move-to-left-margin should stop at field boundaries?  I'm not
sure this is the correct solution...

Alex.
-- 
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