bug#43003: 28.0.50; comint-password-prompt-regexp too restrictive

[Robert Pluim]

>>>>> On Mon, 31 Aug 2020 11:26:10 +0200, Stephen Berman 
>>>>> <stephen.berman@gmx.net> said:

    Stephen> On Sun, 30 Aug 2020 15:41:57 +0200 Lars Ingebrigtsen 
<larsi@gnus.org> wrote:
    >> Stephen Berman <stephen.berman@gmx.net> writes:
    >> 
    >>> True, I wasn't thinking about that.  Then I guess it's best to leave
    >>> comint-password-prompt-regexp as is and I'll just change it locally.
    >>> The problem I have with it doesn't seem to be widespread, to say the
    >>> least.  So feel free to close the bug.
    >> 
    >> OK; done.

    Stephen> A postscript with additional datapoints: In my OP, the the system 
that
    Stephen> the problem occurs on (Linux From Scratch) uses openssh 8.2p1, 
while the
    Stephen> system without the problem (an older Linux From Scratch) uses 
openssh
    Stephen> 7.9p1.  I've now reproduced the problem on two other GNU/Linux 
systems:
    Stephen> current openSUSE Tumbleweed, which uses openssh 8.3p1 (and I see 
the
    Stephen> problem here on two different machines), and openSUSE Leap 15.2, 
which
    Stephen> uses openssh 8.1p1.  This supports my conjecture that the 
problematic
    Stephen> carriage return in the prompt comes from openssh.  If anyone else
    Stephen> running a system with openssh 8.{1,2,3}p1 can reproduce the 
problem,
    Stephen> then perhaps a different way of handling it than changing the 
default
    Stephen> value of comint-password-prompt-regexp can be found.

That matches the analysis done in

https://emacs.stackexchange.com/questions/60394/unable-to-push-into-github-using-magit

which leads to:

https://github.com/magit/magit/issues/3843

TL;DR magit decided to strip the \r from the prompt received from
openssh.

We could strip control characters in comint-watch-for-password-prompt,
but then people who've legitimately put control characters in
comint-password-prompt-regexp will get annoyed.

Perhaps just strip '\r'? (And document it, of course)

diff --git a/lisp/comint.el b/lisp/comint.el
index be0e32b9e0..74c5c7f94f 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -2427,7 +2427,8 @@ comint-watch-for-password-prompt
 
 This function could be in the list `comint-output-filter-functions'."
   (when (let ((case-fold-search t))
-         (string-match comint-password-prompt-regexp string))
+         (string-match comint-password-prompt-regexp
+                        (replace-regexp-in-string "\r" "" string)))
     (when (string-match "^[ \n\r\t\v\f\b\a]+" string)
       (setq string (replace-match "" t t string)))
     (let ((comint--prompt-recursion-depth (1+ comint--prompt-recursion-depth)))