org-insert-item, indent causes a soft freeze or error message

[Duianto - <otnaiud@gmail.com>]

Hello

Depending on the indentation amount on the line following a list item,
when (org-insert-item) is evaluated.

Causes Emacs to soft freeze (can be canceled by pressing: C-g)
or an error message is shown: (args-out-of-range 0 1)


Reproduction Steps:

Copy the following lines:
1. a
   b
2. c

(the second line is indented by 3 spaces)

Open a new buffer: C-x b test.org RET
Switch to org mode: M-x org-mode RET
Paste the copied lines: C-y
Move the cursor to the end of the first line, after the: a
(if the cursor is before the a, then the list item is added on a new line above
probably as expected)
Evaluate the following command: S-M-; (org-insert-item) RET

Observed:
The only visible change is that the cursor moves to the beginning of
the "Eval:" prompt in the minibuffer.
The Emacs cpu usage spikes (an infinite loop?)
The soft freeze can be canceled by pressing: C-g
The buffer now shows:
1. a
1.
   b
2. c

The initial example above had three spaces before the: b
The same soft freeze is observed if more spaces are added before the: b
(I only tested it, up to five spaces, but I there might not be an upper limit)

Indented by one or two spaces:
If the initial second line is indented with one or two spaces, then
Emacs shows an error message instead of freezing.
A Backtrace buffer opens with the message:

Debugger entered--Lisp error: (args-out-of-range 0 1)
  replace-match("1. " nil nil nil 1)
  #f(compiled-function (struct old-struct item) #<bytecode
0x497071>)(((1 0 "1. " nil nil nil 6) (6 0 "2. " nil nil nil 13) (16 0
"1. " nil nil nil 20)) ((1 0 "1. " nil nil nil 6) (6 0 "1. " nil nil
nil 13) (16 0 "2. " nil nil nil 20)) 16)
  org-list-struct-apply-struct(((1 0 "1. " nil nil nil 6) (6 0 "2. "
nil nil nil 13) (16 0 "1. " nil nil nil 20)) ((1 0 "1. " nil nil nil
6) (6 0 "1. " nil nil nil 13) (16 0 "2. " nil nil nil 20)))
  org-list-write-struct(((1 0 "1. " nil nil nil 6) (6 0 "2. " nil nil
nil 13) (16 0 "1. " nil nil nil 20)) ((1) (6) (16)))
  org-insert-item()
  eval((org-insert-item) nil)
  eval-expression((org-insert-item) nil nil 127)
  funcall-interactively(eval-expression (org-insert-item) nil nil 127)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)


No indentation:
If the indentation is removed from the second line:
1. a
b
2. c

Then it might be working as expected:
1. a
2.
b
2. c

a correctly numbered list item is inserted.

The fourth lines list number: 2. c
didn't change, but it might be expected since there was no indentation
before the: b
therefore it might be assumed that the list ended there.

At least Emacs didn't freeze or show any errors.


System info:
Org mode version 9.3.7 (9.3.7-4-gba6ca7-elpaplus @
c:/Users/username/.emacs.d/elpa/org-plus-contrib-20200622/)
GNU Emacs 26.3 (build 1, x86_64-w64-mingw32) of 2019-08-29
Windows 1903