bug#12145: Fix causes problems with other processes

[Thomas Koch]

The fix for this bug seems to cause a problem with "concurrent" processes over 
SSH with ControlMaster, see https://debbugs.gnu.org/61350

For testing I've removed the JUST-THIS-ONE arguments from all 
accept-process-output calls in Tramp. Afterwards the bug can still be 
reproduced in tramp 2.6.0 as described above.

At this point I wanted to paste the backtrace of the issue. However I found 
myself unable to reproduce the issue a second time. Only after I started eglot, 
I could trigger actually two different backtraces, depending on the starting 
folder for `find-name-dired` or the pattern.


Debugger entered--Lisp error: (wrong-type-argument processp nil)
  set-process-filter(nil find-dired-filter)
  find-dired("/blacky:/home/thk/git/yacy_search_server/source/ne..." "-name 
\\*.java")
  find-name-dired("/blacky:/home/thk/git/yacy_search_server/source/ne..." 
"*.java")
  funcall-interactively(find-name-dired 
"/blacky:/home/thk/git/yacy_search_server/source/ne..." "*.java")
  call-interactively(find-name-dired record nil)
  command-execute(find-name-dired record)
  execute-extended-command(nil "find-name-dired" nil)
  funcall-interactively(execute-extended-command nil "find-name-dired" nil)
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)


Debugger entered--Lisp error: (wrong-type-argument "markerp nil")
  signal(wrong-type-argument ("markerp nil"))
  tramp-error((tramp-file-name #("scp" 0 3 (tramp-default t)) nil nil "blacky" 
nil "/home/thk/git/yacy_search_server/.dir-locals.el" nil) wrong-type-argument 
"markerp nil")
  tramp-signal-hook-function(wrong-type-argument (markerp nil))
  comint-output-filter(#<process *Find*> "    74785      4 -rw-r--r--   1 thk   
   thk      ...")
  accept-process-output(#<process *tramp/scp blacky*> nil nil t)
  tramp-accept-process-output(#<process *tramp/scp blacky*>)
  tramp-wait-for-regexp(#<process *tramp/scp blacky*> nil 
"\\(?:^\\|\0\\)\\(?:[^\n#$]*///ad07405faf7fa5751ee9747c48...")
  tramp-wait-for-output(#<process *tramp/scp blacky*>)
  tramp-send-command((tramp-file-name #("scp" 0 3 (tramp-default t)) nil nil 
"blacky" nil "/home/thk/git/yacy_search_server/.dir-locals.el" nil) "test -r 
/home/thk/git/yacy_search_server/.dir-loca...")
  tramp-send-command-and-check((tramp-file-name #("scp" 0 3 (tramp-default t)) 
nil nil "blacky" nil "/home/thk/git/yacy_search_server/.dir-locals.el" nil) 
"test -r /home/thk/git/yacy_search_server/.dir-loca...")
  tramp-run-test("-r" "/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  
tramp-sh-handle-file-readable-p("/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  apply(tramp-sh-handle-file-readable-p 
"/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  tramp-sh-file-name-handler(file-readable-p 
"/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  apply(tramp-sh-file-name-handler file-readable-p 
"/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  tramp-file-name-handler(file-readable-p 
"/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  file-readable-p("/blacky:/home/thk/git/yacy_search_server/.dir-loca...")
  dir-locals--all-files("/blacky:/home/thk/git/yacy_search_server/")
  locate-dominating-file("/blacky:/home/thk/git/yacy_search_server/" 
dir-locals--all-files)
  dir-locals-find-file("/blacky:/home/thk/git/yacy_search_server/")
  hack-dir-local-variables()
  hack-dir-local-variables-non-file-buffer()
  dired-mode("/blacky:/home/thk/git/yacy_search_server/" "-dilsb")
  find-dired("/blacky:/home/thk/git/yacy_search_server/" "-name \\*.bat")
  find-name-dired("/blacky:/home/thk/git/yacy_search_server/" "*.bat")
  funcall-interactively(find-name-dired 
"/blacky:/home/thk/git/yacy_search_server/" "*.bat")
  call-interactively(find-name-dired record nil)
  command-execute(find-name-dired record)
  execute-extended-command(nil "find-name-dired" nil)
  funcall-interactively(execute-extended-command nil "find-name-dired" nil)
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)


I'd like to try to understand this bug better and to find a fix that does not 
set JUST-THIS-ONE to t. Any help is appreciated.