Re: Emacs 23.1 flushes stdin on startup

[Ted Zlatanov]

The following message is a courtesy copy of an article
that has been posted to gnu.emacs.help as well.

On Wed, 05 Aug 2009 00:33:56 +0200 address@hidden (Johan Bockgård) wrote: 

JB> "David F. Skoll" <address@hidden> writes:
>> I've noticed a behavior change in 23.1 that doesn't seem to be documented:
>> If I start Emacs in text mode (eg: "emacs -nw") and type stuff before
>> Emacs has started up, the stuff I type is lost.  Version 22 would not
>> flush the input, and my pre-startup stuff would appear in the buffer.

JB> It's caused by the xterm init code (info "(elisp) Terminal-Specific")
JB> for finding out if the terminal is modern enough to support the
JB> `modifyOtherKeys' feature; see term/xterm.el.

JB>       [...]
JB>       ;; Pending input can be mistakenly returned by the calls to
JB>       ;; read-event below.  Discard it.
JB>       (discard-input)
JB>       ;; Try to find out the type of terminal by sending a "Secondary
JB>       ;; Device Attributes (DA)" query.
JB>       (send-string-to-terminal "\e[>0c")

>> I really miss the old behavior.  Is there any way to convince Emacs 23.1
>> not to flush stdin on startup?

JB> There's no simple knob, unfortunately, but there's always some way.

How about adding a variable xterm-modify-other-keys-supported with
values t, nil, and 'check?  It would make the startup slightly faster,
too.

Small untested patch attached to illustrate.

Ted

Index: xterm.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/term/xterm.el,v
retrieving revision 1.62
diff -c -r1.62 xterm.el
*** xterm.el    5 Jan 2009 03:23:59 -0000       1.62
--- xterm.el    5 Aug 2009 13:59:26 -0000
***************
*** 25,30 ****
--- 25,36 ----
  
  ;;; Code:
  
+ (defcustom xterm-modify-other-keys-supported 'check
+   "Whether the XTerm supports modifyOtherKeys."
+   :type '(choice (const :tag "No" nil)
+                (const :tag "Yes" t)
+                (const :tag "Check" check)))
+ 
  (defvar xterm-function-map
    (let ((map (make-sparse-keymap)))
  
***************
*** 470,515 ****
      ;; C-. C-, etc.
      ;; To do that we need to find out if the current terminal supports
      ;; modifyOtherKeys. At this time only xterm does.
!     (let ((coding-system-for-read 'binary)
!         (chr nil)
!         (str nil))
!       ;; Pending input can be mistakenly returned by the calls to
!       ;; read-event below.  Discard it.
!       (discard-input)
!       ;; Try to find out the type of terminal by sending a "Secondary
!       ;; Device Attributes (DA)" query.
!       (send-string-to-terminal "\e[>0c")
! 
!       ;; The reply should be of the form: \e [ > NUMBER1 ; NUMBER2 ; NUMBER3 c
!       ;; If the timeout is completely removed for read-event, this
!       ;; might hang for terminals that pretend to be xterm, but don't
!       ;; respond to this escape sequence.  RMS' opinion was to remove
!       ;; it completely.  That might be right, but let's first try to
!       ;; see if by using a longer timeout we get rid of most issues.
!       (when (equal (read-event nil nil 2) ?\e)
!       (when (equal (read-event nil nil 2) ?\[)
!         (while (not (equal (setq chr (read-event nil nil 2)) ?c))
!           (setq str (concat str (string chr))))
!         (when (string-match ">0;\\([0-9]+\\);0" str)
!           ;; NUMBER2 is the xterm version number, look for something
!           ;; greater than 216, the version when modifyOtherKeys was
!           ;; introduced.
!           (when (>= (string-to-number
!                      (substring str (match-beginning 1) (match-end 1))) 216)
!             ;; Make sure that the modifyOtherKeys state is restored when
!             ;; suspending, resuming and exiting.
!             (add-hook 'suspend-hook 'xterm-turn-off-modify-other-keys)
!             (add-hook 'suspend-resume-hook 'xterm-turn-on-modify-other-keys)
!             (add-hook 'kill-emacs-hook 'xterm-remove-modify-other-keys)
!             (add-hook 'delete-terminal-functions 
'xterm-remove-modify-other-keys)
!             ;; Add the selected frame to the list of frames that
!             ;; need to deal with modify-other-keys.
!             (push (frame-terminal (selected-frame))
!                   xterm-modify-other-keys-terminal-list)
!             (xterm-turn-on-modify-other-keys))))))
  
      (run-hooks 'terminal-init-xterm-hook))
  
  ;; Set up colors, for those versions of xterm that support it.
  (defvar xterm-standard-colors
    ;; The names in the comments taken from XTerm-col.ad in the xterm
--- 476,529 ----
      ;; C-. C-, etc.
      ;; To do that we need to find out if the current terminal supports
      ;; modifyOtherKeys. At this time only xterm does.
!     (when xterm-modify-other-keys-supported
!       (cond
!        ((eq xterm-modify-other-keys-supported 'check)
!       (let ((coding-system-for-read 'binary)
!             (chr nil)
!             (str nil))
!         ;; Pending input can be mistakenly returned by the calls to
!         ;; read-event below.  Discard it.
!         (discard-input)
!         ;; Try to find out the type of terminal by sending a "Secondary
!         ;; Device Attributes (DA)" query.
!         (send-string-to-terminal "\e[>0c")
! 
!         ;; The reply should be of the form: \e [ > NUMBER1 ; NUMBER2 ; 
NUMBER3 c
!         ;; If the timeout is completely removed for read-event, this
!         ;; might hang for terminals that pretend to be xterm, but don't
!         ;; respond to this escape sequence.  RMS' opinion was to remove
!         ;; it completely.  That might be right, but let's first try to
!         ;; see if by using a longer timeout we get rid of most issues.
!         (when (equal (read-event nil nil 2) ?\e)
!           (when (equal (read-event nil nil 2) ?\[)
!             (while (not (equal (setq chr (read-event nil nil 2)) ?c))
!               (setq str (concat str (string chr))))
!             (when (string-match ">0;\\([0-9]+\\);0" str)
!               ;; NUMBER2 is the xterm version number, look for something
!               ;; greater than 216, the version when modifyOtherKeys was
!               ;; introduced.
!               (when (>= (string-to-number
!                          (substring str (match-beginning 1) (match-end 1))) 
216)
!                 (terminal-init-xterm-modify-other-keys)))))))
!        (t (terminal-init-xterm-modify-other-keys))))
  
      (run-hooks 'terminal-init-xterm-hook))
  
+ (defun terminal-init-xterm-modify-other-keys ()
+   "Terminal initialization for xterm's modifyOtherKeys support."
+   ;; Make sure that the modifyOtherKeys state is restored when
+   ;; suspending, resuming and exiting.
+   (add-hook 'suspend-hook 'xterm-turn-off-modify-other-keys)
+   (add-hook 'suspend-resume-hook 'xterm-turn-on-modify-other-keys)
+   (add-hook 'kill-emacs-hook 'xterm-remove-modify-other-keys)
+   (add-hook 'delete-terminal-functions 'xterm-remove-modify-other-keys)
+   ;; Add the selected frame to the list of frames that
+   ;; need to deal with modify-other-keys.
+   (push (frame-terminal (selected-frame))
+       xterm-modify-other-keys-terminal-list)
+   (xterm-turn-on-modify-other-keys))
+ 
  ;; Set up colors, for those versions of xterm that support it.
  (defvar xterm-standard-colors
    ;; The names in the comments taken from XTerm-col.ad in the xterm