Re: PATCH: $PREDISPLAY/$POSTDISPLAY

[Peter Stephenson <pws@csr.com>]

Sven Wischnowsky wrote:
> Peter Stephenson wrote:
> > Note the way these parameters survive across invocations of zle.  This
> > was simply because it was the most natural way of writing it.  We can
> > make zleread() reinitialise them if it seems preferable.
> 
> I can see that it's more powerful, but it's really rather irritating,
> isn't it? Especially since you can't make them go away from the
> (normal) command line. Although with well-behaved widgets...

Yes, I came to that conclusion, too.

> It could also be nice if we could restrict
> the allowed movement-range in recursive edits (kind of like
> narrow-to-region in emacs).

You can already do this bit, with the same limitation as the Emacs
function, i.e. the editable region is always the bit in the middle.

narrow-to-region() {
  # Restrict the start of the editable line to the position
  # between MARK and CURSOR

  local lbuffer rbuffer
  integer start=$MARK end=$CURSOR swap

  if (( start == end )); then
    return 1
  elif (( start > end )); then
    swap=start
    start=end
    end=swap
  fi

  (( end++ ))

  PREDISPLAY=${BUFFER[1,start]}
  lbuffer=$PREDISPLAY
  POSTDISPLAY=${BUFFER[end,-1]}
  rbuffer=$POSTDISPLAY
  BUFFER=${BUFFER[start+1,end-1]}
  if (( swap )); then 
    CURSOR=0 
    MARK=${#BUFFER}
  else
    MARK=0
    CURSOR=${#BUFFER}
  fi

  zle recursive-edit

  PREDISPLAY=
  POSTDISPLAY=
  LBUFFER="$lbuffer$LBUFFER"
  RBUFFER="$RBUFFER$rbuffer"
}

Obviously, you can easily modify this to make the text outside the
region display as "...", and so on.  You might want to make accept-line
a dummy during this and define a widget `widen' which calls
.accept-line, or make the normal accept-line set a flag that
restrict-start will propagate the accept-line upwards, or something.

To be consistent, it would be better not to assume PREDISPLAY and
POSTDISPLAY are empty, i.e. we should really set predisplay=$PREDISPLAY,
PREDISPLAY+=... before and PREDISPLAY=$predisplay after, but I got bored
at that point.

There could be lurking off-by-one errors, but it seemed to do roughly
what I expected.

Index: Doc/Zsh/zle.yo
===================================================================
RCS file: /cvsroot/zsh/zsh/Doc/Zsh/zle.yo,v
retrieving revision 1.24
diff -u -r1.24 zle.yo
--- Doc/Zsh/zle.yo	1 Jul 2002 16:50:43 -0000	1.24
+++ Doc/Zsh/zle.yo	4 Jul 2002 09:28:36 -0000
@@ -666,17 +666,15 @@
 item(tt(PREDISPLAY) (scalar))(
 Text to be displayed before the start of the editable text buffer.  This
 does not have to be a complete line; to display a complete line, a newline
-must be appended explicitly.  Note that the text survives between calls to zle
-and hence must be removed explicitly by assigning an empty value to the
-parameter.
+must be appended explicitly.    The text is reset on each new invocation
+(but not recursive invocation) of zle.
 )
 vindex(POSTDISPLAY)
 item(tt(POSTDISPLAY) (scalar))(
 Text to be displayed after the end of the editable text buffer.  This
 does not have to be a complete line; to display a complete line, a newline
-must be prepended explicitly.  Note that the text survives between calls to
-zle and hence must be removed explicitly by assigning an empty value to the
-parameter.
+must be prepended explicitly.  The text is reset on each new invocation
+(but not recursive invocation) of zle.
 )
 vindex(RBUFFER)
 item(tt(RBUFFER) (scalar))(
Index: Src/Zle/zle_main.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/Zle/zle_main.c,v
retrieving revision 1.25
diff -u -r1.25 zle_main.c
--- Src/Zle/zle_main.c	1 Jul 2002 09:54:48 -0000	1.25
+++ Src/Zle/zle_main.c	4 Jul 2002 09:28:36 -0000
@@ -752,6 +752,7 @@
     pmpt_attr = txtchange;
     rpromptbuf = promptexpand(rp, 1, NULL, NULL);
     rpmpt_attr = txtchange;
+    free_prepostdisplay();
 
     zlereadflags = flags;
     histline = curhist;
Index: Src/Zle/zle_params.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/Zle/zle_params.c,v
retrieving revision 1.5
diff -u -r1.5 zle_params.c
--- Src/Zle/zle_params.c	1 Jul 2002 16:50:43 -0000	1.5
+++ Src/Zle/zle_params.c	4 Jul 2002 09:28:36 -0000
@@ -516,3 +516,13 @@
 {
     return get_prepost(postdisplay, postdisplaylen);
 }
+
+/**/
+void
+free_prepostdisplay(void)
+{
+    if (predisplaylen)
+	set_prepost(&predisplay, &predisplaylen, NULL);
+    if (postdisplaylen)
+	set_prepost(&postdisplay, &postdisplaylen, NULL);
+}

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 392070


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