Re: Phil's prompt is not working when LANG is set to UTF-8

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Sat, 16 Feb 2008 11:13:35 -0800
Bart Schaefer <schaefer@brasslantern.com> wrote:
> On Feb 15, 11:52pm, Peter Stephenson wrote:
> }
> } - Hence it falls foul of the multibyte tests.  In principle it
> }   might clash with a UTF-8 character anyway and have the wrong
> }   width, so assuming a width 1 for an unknown character is not
> }   necessarily better than assuming width 0.
> 
> I agree with "not necessarily," but I suspect it'll be right more
> often than wrong to assume 1.  *Most* characters are not going to be
> "non-printing," and if the mb library doesn't recognize them, then
> they're also unlikely to be simultaneously multibyte and handled
> correctly by the terminal.

OK, I'll change that (though needless to say the %G method is
still recommended as being less hit and miss).

> I like this, but I'm wondering if it might not be better to have %{
> accept a count, e.g., instead of %{...%6G%} just write %6{...%}.

That was my originally thought, but then I realisd that as far as the
code is concerned they're logically independent.  From the point of view
of the user it's a rather different matter, however.  It's trivial to
support both.

> Does it matter where %G appears?  %{...%7G...%} ?

Because they're indepdendent, it doesn't matter at all, and multiple
uses acumulate.  In fact, they don't actually need to appear within
the %{...%}, although there's no obvious reason to put them elsewhere.

> Ooh, and what about negative numbers?  Can one say %-4G to mean that
> the sequence actually moved the cursor to the LEFT four positions?
> *That* could be really useful.

Yes, but I picked the present change because it was already supported by
the backend code.  Additions like the above are another story.

Index: Doc/Zsh/prompt.yo
===================================================================
RCS file: /cvsroot/zsh/zsh/Doc/Zsh/prompt.yo,v
retrieving revision 1.10
diff -u -r1.10 prompt.yo
--- Doc/Zsh/prompt.yo	15 Feb 2008 23:59:09 -0000	1.10
+++ Doc/Zsh/prompt.yo	17 Feb 2008 16:42:43 -0000
@@ -187,6 +187,9 @@
 Include a string as a literal escape sequence.
 The string within the braces should not change the cursor
 position.  Brace pairs can nest.
+
+A positive numeric argument between the tt(%) and the %%({) is treated as
+described for tt(%G) below.
 )
 item(tt(%G))(
 Within a tt(%{)...tt(%}) sequence, include a `glitch': that is, assume
@@ -199,6 +202,9 @@
 indicates a character width other than one.  Hence tt(%{)var(seq)tt(%2G%})
 outputs var(seq) and assumes it takes up the width of two standard
 characters.
+
+Multiple uses of tt(%G) accumulate in the obvious fashion; the position
+of the tt(%G) is unimportant.  Negative integers are not handled.
 )
 enditem()
 
Index: Src/prompt.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/prompt.c,v
retrieving revision 1.45
diff -u -r1.45 prompt.c
--- Src/prompt.c	15 Feb 2008 23:59:09 -0000	1.45
+++ Src/prompt.c	17 Feb 2008 16:42:43 -0000
@@ -472,7 +472,10 @@
 		    addbufspc(1);
 		    *bp++ = Inpar;
 		}
-		break;
+		if (arg <= 0)
+		    break;
+		/* else */
+		/* FALLTHROUGH */
 	    case 'G':
 		if (arg > 0) {
 		    addbufspc(arg);
@@ -948,9 +951,11 @@
 		break;
 	    case MB_INVALID:
 		memset(&mbs, 0, sizeof mbs);
-		/* FALL THROUGH */
+		/* Invalid character: assume single width. */
+		multi = 0;
+		w++;
+		break;
 	    case 0:
-		/* Invalid character or null: assume no output. */
 		multi = 0;
 		break;
 	    default:

-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/