fix multiple bugs in countprompt

1. Height off by one in the presence of meta characters at the end of the line.

The following prompt has height 2 but countprompt used to return 3.

    PROMPT="${(pl.$COLUMNS..-.)}%f"$'\n'

You can observe the effects of the bug with esc-x followed by reset-prompt.

2. Width off by one when a line is broken in the middle of a wide character.

Assuming COLUMNS=79, the following prompt has width 2 but countprompt used to return 0.

    PROMPT="${(pl.40..\u3050.)}" zsh -df

Press ctrl-r or type ls<tab> to observe the effects of the bug.

3. Width off by 1-7 when a line is broken in the middle of a tab.

Assuming COLUMNS=79, the following prompt has width 1 but countprompt used to return 0.

    PROMPT="${(pl.10..\t.)}" zsh -df

Press Ctrl-R or type ls<TAB> to observe the effects of the bug.

1 files changed, 27 insertions, 8 deletions

diff --git a/Src/prompt.c b/Src/prompt.c
index e8d50d161..7f4d7a70e 100644
--- a/Src/prompt.c
+++ b/Src/prompt.c
@@ -1075,10 +1075,9 @@ putstr(int d)
 mod_export void
 countprompt(char *str, int *wp, int *hp, int overf)
 {
-    int w = 0, h = 1, multi = 0;
+    int w = 0, h = 1, multi = 0, wcw = 0;
     int s = 1;
 #ifdef MULTIBYTE_SUPPORT
-    int wcw;
     char inchar;
     mbstate_t mbs;
     wchar_t wc;
@@ -1092,10 +1091,23 @@ countprompt(char *str, int *wp, int *hp, int overf)
 	 * prompt and the line it terminates takes up exactly the width of the
 	 * terminal
 	 */
-	if (w >= zterm_columns && overf >= 0 && !multi && *str != '\n') {
-	    w = 0;
+	while (w > zterm_columns && overf >= 0 && !multi) {
 	    h++;
+	    if (wcw) {
+		/*
+		 * Wide characters don't get split off. They move to the
+		 * next line if there is not enough space.
+		 */
+		w = wcw;
+		break;
+	    } else {
+		/*
+		 * Tabs overflow to the next line as if they were made of spaces.
+		 */
+		w -= zterm_columns;
+	    }
 	}
+	wcw = 0;
 	/*
 	 * Input string should be metafied, so tokens in it should
 	 * be real tokens, even if there are multibyte characters.
@@ -1176,12 +1188,19 @@ countprompt(char *str, int *wp, int *hp, int overf)
      * This isn't easy to handle generally; just assume there's no
      * output.
      */
-    if(w >= zterm_columns && overf >= 0) {
-	if (!overf || w > zterm_columns) {
-	    w = 0;
-	    h++;
+    while (w > zterm_columns && overf >= 0) {
+	h++;
+	if (wcw) {
+	    w = wcw;
+	    break;
+	} else {
+	    w -= zterm_columns;
 	}
     }
+    if (w == zterm_columns && overf == 0) {
+	w = 0;
+	h++;
+    }
     if(wp)
 	*wp = w;
     if(hp)