Avoid printing a [0] element for .sh.match

This long overdue bugfix prevents name_match() in init.c from printing a
spurious zero element when using ${!.sh.match}. I haven't been able to
break this bugfix during testing and it's one of the last remaining
issues with .sh.match, so it's about time this is submitted as a pull
request.

(See ksh93#308 (comment)
 and the related comments in the thread.)

NEWS

@@ -7,6 +7,9 @@ Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 - Fixed a rare crash or rare incorrect behaviour in .sh.tilde.{get,set}
   discipline functions for ~ expansion (see 2021-03-16 below).
 
+- Fixed a bug that caused listing the .sh.match variable with ${!.sh.match} to
+  show a spurious zero element.
+
 2024-01-22:
 
 - Fixed a bug in the loop invariants optimizer (SHOPT_OPTIMIZE) that caused

src/cmd/ksh93/sh/init.c

@@ -1015,7 +1015,10 @@ static char* get_match(Namval_t* np, Namfun_t *fp)
 static char *name_match(Namval_t *np, Namfun_t *fp)
 {
 	int sub = nv_aindex(SH_MATCHNOD);
-	sfprintf(sh.strbuf,".sh.match[%d]",sub);
+	if(sub==0)
+		sfprintf(sh.strbuf,".sh.match");
+	else
+		sfprintf(sh.strbuf,".sh.match[%d]",sub);
 	return sfstruse(sh.strbuf);
 }
 

src/cmd/ksh93/tests/variables.sh

@@ -1650,5 +1650,12 @@ done
 unset i got bound
 SRANDOM=0
 
+# ======
+# Avoid printing a [0] element for .sh.match
+exp='.sh.match'
+got=${ $SHELL -c 'print ${!.sh.match}' }
+[[ $exp == "$got" ]] || err_exit "'print \${!.sh.match}' should not print a [0] subscript" \
+	"(expected ${ printf %q "$exp" }, got ${ printf %q "$got" })"
+
 # ======
 exit $((Errors<125?Errors:125))