PATCH: Polite output from traps with zle active

[Peter Stephenson <pws@csr.com>]

In parallel to Sven's changes for traps, here is something I have wanted
for some time:  the ability for traps to keep the line editing display neat
in the same way that e.g. information from exiting background jobs has
always done.  It alters zle -R to allow it to be called when zle is not
active --- it simply returns zero --- and adds `zle -I' (invalidate), which
simply calls trashzle().  Both are allowed when zle is not active (and do
nothing) because there is no good reason for forcing the onus of deciding
whether the display needs to be cleared and refreshed onto the writer of the
trap function.  So a prototype is:

TRAPUSR1() {
  zle -I
  print Hello, I am output
  zle -R
}

It's possible there are extra safeguards I should have added but missed.
If anyone thinks this should be done a different way, now would be a good
time to mention it.

I probably won't commit this at the moment, anyway, because my zle_main.c
has Sven's trap changes mixed in it --- maybe they can eventually go in
together.

Index: Src/Zle/zle_main.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/Zle/zle_main.c,v
retrieving revision 1.13
diff -u -r1.13 zle_main.c
--- Src/Zle/zle_main.c	2000/10/22 02:34:19	1.13
+++ Src/Zle/zle_main.c	2000/11/02 11:08:56
@@ -1083,7 +1092,7 @@
 static struct builtin bintab[] = {
     BUILTIN("bindkey", 0, bin_bindkey, 0, -1, 0, "evaMldDANmrsLR", NULL),
     BUILTIN("vared",   0, bin_vared,   1,  7, 0, NULL,             NULL),
-    BUILTIN("zle",     0, bin_zle,     0, -1, 0, "lDANCLmMgGcRaU", NULL),
+    BUILTIN("zle",     0, bin_zle,     0, -1, 0, "lDANCLmMgGcRaUI", NULL),
 };
 
 /* The order of the entries in this table has to match the *HOOK
Index: Src/Zle/zle_thingy.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/Zle/zle_thingy.c,v
retrieving revision 1.2
diff -u -r1.2 zle_thingy.c
--- Src/Zle/zle_thingy.c	2000/07/13 09:11:54	1.2
+++ Src/Zle/zle_thingy.c	2000/11/02 11:08:56
@@ -339,6 +339,7 @@
 	{ 'R', bin_zle_refresh, 0, -1 },
 	{ 'M', bin_zle_mesg, 1, 1 },
 	{ 'U', bin_zle_unget, 1, 1 },
+	{ 'I', bin_zle_invalidate, 0, 0 },
 	{ 0,   bin_zle_call, 0, -1 },
     };
     struct opn const *op, *opp;
@@ -396,10 +397,8 @@
     char *s = statusline;
     int sl = statusll, ocl = clearlist;
 
-    if (!zleactive) {
-	zwarnnam(name, "can only be called from widget function", NULL, 0);
-	return 1;
-    }
+    if (!zleactive)
+	return 0;
     statusline = NULL;
     statusll = 0;
     if (*args) {
@@ -654,6 +653,14 @@
     if (saveflag)
 	zmod = modsave;
     return ret;
+}
+
+/**/
+static int
+bin_zle_invalidate(char *name, char **args, char *ops, char func)
+{
+    trashzle();
+    return 0;
 }
 
 /*******************/
Index: Doc/Zsh/mod_zle.yo
===================================================================
RCS file: /cvsroot/zsh/zsh/Doc/Zsh/mod_zle.yo,v
retrieving revision 1.8
diff -u -r1.8 mod_zle.yo
--- Doc/Zsh/mod_zle.yo	2000/09/11 07:08:28	1.8
+++ Doc/Zsh/mod_zle.yo	2000/11/02 11:08:56
@@ -198,6 +198,7 @@
 xitem(tt(zle) tt(-R) [ tt(-c) ] [ var(display-string) ] [ var(string) ... ])
 xitem(tt(zle) tt(-M) var(string))
 xitem(tt(zle) tt(-U) var(string))
+xitem(tt(zle) tt(-I))
 xitem(tt(zle) var(widget) tt([ -n) var(num) tt(]) tt([ -N ]) var(args) ...)
 item(tt(zle))(
 The tt(zle) builtin performs a number of different actions concerning
@@ -263,6 +264,12 @@
 Note that this option is only useful for widgets that do not exit
 immediately after using it because the strings displayed will be erased 
 immediately after return from the widget.
+
+This command can safely be called outside user defined widgets; if zle is
+active, the display will be refreshed, while if zle is not active, the
+command has no effect.  This is useful for trap functions, which may be
+called while zle is active, in order to tidy up the display on exit.
+In this case there will usually be no other arguments.
 )
 item(tt(-M) var(string))(
 As with the tt(-R) option, the var(string) will be displayed below the 
@@ -280,6 +287,27 @@
 the last string pushed onto the stack will be processed first.  However,
 the characters in each var(string) will be processed in the order in which
 they appear in the string.
+)
+item(tt(-I))(
+Unusually, this option is only useful em(outside) ordinary widget functions.
+It invalidates the current zle display in preparation for output; usually
+this will be from a trap function.  As it has no effect if zle is not
+active, a safe idiom for ensuring that output from traps interacts cleanly
+with text being edited is:
+
+example(TRAPUSR1() {
+    # Invalidate zle display
+  zle -I
+    # Show output
+  print Hello
+    # Refresh display
+  zle -R
+})
+
+Note that there are better ways of manipulating the display from within zle
+widgets.  In general, the trap function may need to test whether zle is
+loaded before using this method; if it is not, there is no point in loading
+it specially since the line editor will not be active.
 )
 item(var(widget) tt([ -n) var(num) tt(]) tt([ -N ]) var(args) ...)(
 Invoke the specified widget.  This can only be done when ZLE is

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
Cambridge Silicon Radio, Unit 300, Science Park, Milton Road,
Cambridge, CB4 0XL, UK                          Tel: +44 (0)1223 392070