bug#67395: Fix "Text is read-only" on backspacing initial calc input

bug#67395: Fix "Text is read-only" on backspacing initial calc input

[George Kuzler]

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This is a one-line fix for a minor issue in calc-mode. When your last
command has caused the minibuffer to open for input - for example,
you've typed a digit - and you immediately press backspace, it should
clear the minibuffer and return you to *Calculator*. Instead, the
minibuffer is unchanged, and emacs prints the message "Text is
read-only". Note that you can then backspace again to delete the
minibuffer contents as normal; this bug only manifests if you try to
backspace right after the command that puts you in the minibuffer.

The issue is that `calcDigit-backspace' tries to clear the minibuffer with
`erase-buffer', which also tries to delete the prompt, which is
read-only. `delete-minibuffer-contents' would have the desired effect
since it doesn't try to delete the prompt. This change just replaces the
former function with the latter.



In GNU Emacs 29.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.8) of 2023-09-24 built on
 e1d0f5fdfea948b9bb25e212c9c623e4
Windowing system distributor 'The X.Org Foundation', version 11.0.12302002
System Description: Fedora Linux 39 (Workstation Edition)

Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var --runstatedir=/run
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xpm --with-x-toolkit=gtk3 --with-gpm=no
 --with-xwidgets --with-modules --with-harfbuzz --with-cairo --with-json
 --with-native-compilation=aot --with-tree-sitter --with-sqlite3
 --with-webp --with-xinput2 build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu CC=gcc 'CFLAGS=-DMAIL_USE_LOCKF -O2
 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches
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 -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS
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 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection
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 LDFLAGS=-Wl,-z,relro
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From: George Kuzler <gkuzler@gmail.com>
Date: Wed, 22 Nov 2023 19:45:55 -0500
Subject: Fix "Text is read-only" on backspacing initial calc input

Immediately after calc-mode opens the minibuffer for input (because you typed a
digit, "e", etc), pressing backspace should clear the minibuffer and return you
to the *Calculator* buffer. Instead, it leaves the minibuffer as-is and prints
the message "Text is read-only"; this is because the function used,
`erase-buffer', tries to erase the read-only minibuffer prompt. Using
`delete-minibuffer-contents' fixes this, since it doesn't attempt to delete the
prompt.

* lisp/calc/calc.el (calcDigit-backspace): Use `delete-minibuffer-contents'
instead of `erase-buffer'.
---
 lisp/calc/calc.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/calc/calc.el b/lisp/calc/calc.el
index b347cc1da23..41aeb17c252 100644
--- a/lisp/calc/calc.el
+++ b/lisp/calc/calc.el
@@ -2491,7 +2491,7 @@ the United States."
 (defun calcDigit-backspace ()
   (interactive)
   (cond ((eq last-command 'calcDigit-start)
-	 (erase-buffer))
+	 (delete-minibuffer-contents))
 	(t (with-suppressed-warnings ((interactive-only backward-delete-char))
              (backward-delete-char 1))))
   (if (= (calc-minibuffer-size) 0)
-- 
2.42.0

bug#67395: Fix "Text is read-only" on backspacing initial calc input

[Eli Zaretskii]

> From: George Kuzler <gkuzler@gmail.com>
> Date: Wed, 22 Nov 2023 21:02:31 -0500
> 
> This is a one-line fix for a minor issue in calc-mode. When your last
> command has caused the minibuffer to open for input - for example,
> you've typed a digit - and you immediately press backspace, it should
> clear the minibuffer and return you to *Calculator*. Instead, the
> minibuffer is unchanged, and emacs prints the message "Text is
> read-only". Note that you can then backspace again to delete the
> minibuffer contents as normal; this bug only manifests if you try to
> backspace right after the command that puts you in the minibuffer.
> 
> The issue is that `calcDigit-backspace' tries to clear the minibuffer with
> `erase-buffer', which also tries to delete the prompt, which is
> read-only. `delete-minibuffer-contents' would have the desired effect
> since it doesn't try to delete the prompt. This change just replaces the
> former function with the latter.

Thanks, I installed this on the emacs-29 branch, and I'm closing the
bug.