Make the minibuffer prompt always have a default argument

Question

Is it possible to make the first history item available as the default argument when running commands like eval-expression and goto-line?

I'd like to be able to just press enter to use the previous value.

I started writing a wrapper around goto-line but thought there must be a more general solution.

To be clearer, here's an example:

1. I run goto-line, type 236 and press enter.
2. I edit around for some time.
3. I run goto-line again and I want to just press enter to go to line 236.

I use helm for M-x and C-x b, but there does not seem to be helm support for these other commands.

Answer 1

[I edited the tags and title: The question is not about the prompt; it's about providing a default value when reading from the minibuffer. That the default is generally shown in the prompt is something else. If no default value has been provided then none will appear in the prompt.]

Whether there's a default value (or several), and what it is, is determined by the read function call (read-from-minibuffer, completing-read etc.), i.e., by the programmer who wrote that call. While reading, it's available in variable minibuffer-default (the value is put there by read-from-minibuffer C code).

You could conceivably advise some basic read functions to add your own chosen default value, but why?

What default value would you want to add, when there isn't one? And when: during the read? And how: interactively or with Lisp? Do you want to impose your own default value, regardless of what's being read? If so, on what basis would you pick that value? Exactly what behavior are you looking for?

If the read function call doesn't provide a default value then you should consider that to be by design (the programmer's choice). You can, however, send a suggestion to the maintainer of the code that makes that function call, suggesting provision of a default value.

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On the other hand, you could add one or more values to the value of minibuffer-history-variable using minibuffer-with-setup-hook. Then you could use M-p to access those values. But you'd either have to do that for an individual read function call or you'd have to advise such a read function.

Answer 2

I am not sure if this will cause any problems when calling some other functions (it is pefectly save to try it), but as mentioned by Drew already, you could advise the 'underlying' functions. For goto-line the following advice should do the trick:

(defun goto-line-advice-default-last (orig-fun &rest args)
  (when-let (hist (nth 2 args))
    (setf (nth 1 args) (string-to-number (car (eval hist)))))
  (apply orig-fun args))

(advice-add 'read-number :around #'goto-line-advice-default-last)

(note that the default value is displayed in the prompt, but/so you can just press RET)

And for eval-expression, the following advice should do it:

(defun eval-expression-advice-default-last (orig-fun &rest args)
  ;; only for eval-expression (so this is configurable)
  (when (string-match-p (car args) "Eval: ")
    (when-let (hist (nth 4 args))
      (if (eq (length args) 5)
          (add-to-list 'args nil t (lambda (a b))))
      (setf (car args) (format "Eval [%s]: " (car (eval hist))))
      (setf (nth 5 args) (car (eval hist)))))
  (apply orig-fun args))

(advice-add 'read-from-minibuffer :around #'eval-expression-advice-default-last)

You can configure where the advice applies via the first conditional (here I am using a when but you could also use an unless, see also the edit history for earlier versions).

Of course, you could additionally remove the item(s) from the history. If you really want that, I'll leave it for you as a nice little lisp exercise :)