GNU bug report logs - #50811
28.0.50; Misleading Docstring for read-string function

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Codruț Constantin Gușoi <mail <at> codrut.pro>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: 28.0.50; Misleading Docstring for read-string function
Date: Sun, 26 Sep 2021 08:28:05 +0000

While trying to solve and issue in an emacs pacage: https://github.com/Alexander-Miller/cfrs/pull/6 I encountered the following docstring entry for the read-string function:


```

If non-nil, second arg INITIAL-INPUT is a string to insert before reading.
  This argument has been superseded by DEFAULT-VALUE and should normally be nil
  in new code.  It behaves as INITIAL-CONTENTS in `read-from-minibuffer' (which
  see).
```


This is misleading since INITIAL-INPUT behaves differently from DEFAULT-VALUE:


```

;; No pre-completed value, returns "" when empty.
(read-string "PROMPT ")

;; Pre-completed with "A", returns "" when empty.
(read-string "PROMPT " "A")

;; Pre-completed with "A", returns "B" when empty.
(read-string "PROMPT " "A" nil "B")

;; No pre-completed value, returns "B" when empty.
(read-string "PROMPT " nil nil "B")

```


Not sure what should be done here, either remove that note, since both arguments do a different job, or change the code to pass around DEFAULT-VALUE instead of INITIAL-INPUT internally when INITIAL-INPUT is nil, as the docstring suggests. But the latter feels weird to me as getting rid of INITIAL-INPUT would be a breaking change so it's probably never going to be removed from the arguments list. Also I am not sure what the initial intention of superseding INITIAL-INPUT was.


Let me know what you think works best and I can submit patches.

Cheers,
Codruț

www.codrut.pro

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