Fix field separator for $* in here-document

Reproducer:

    IFS=/
    set a b c
    cat <<EOF
    $*
    EOF

Actual output: a b c
Expected output: a/b/c

In any context in which field splitting is not possible, POSIX
specifies that $* uses the first character of $IFS as the output
field separator.[*] Here-documents are such a context.

Analysis: In macro.c, there are three places where IFS is
initialised - in sh_mactrim, sh_macexpand and in sh_machere. The
latter function deals with here-documents. IFS is initialised by
pointing ifsp to the value of IFSNOD and setting ifs to the first
byte of this value. However, in sh_machere, ifs is hardcoded to a
space. This is the bug.

src/cmd/ksh93/sh/macro.c:
- Add setup_ifs function to centralise this logic.
- Call setup_ifs in the three places mentioned, replacing the
  duplicative old code (including the buggy version).

[*] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_05_02

Author: McDutchie

NEWS

@@ -2,6 +2,12 @@ This documents significant changes in the dev branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2025-04-24:
+
+- Fixed a bug in the expansion of $* within a here-document: the positional
+  parameters were separated by a hardcoded space instead of the first
+  character of $IFS (which defaults to a space but can be changed).
+
 2025-04-23:
 
 - [v1.1] Ksh now supports the bash-like case modification expansions

src/cmd/ksh93/sh/macro.c

@@ -145,6 +145,19 @@ char *sh_mactry(char *string)
 	return "";
 }
 
+/*
+ * Read $IFS and initialize:
+ * - ifsp: pointer to value of IFS (NULL if IFS is unset)
+ * - ifs: first byte of value of IFS (0 if empty, space if IFS is unset)
+ */
+static void setup_ifs(Mac_t *mp)
+{
+	if(mp->ifsp = nv_getval(sh_scoped(IFSNOD)))
+		mp->ifs = *mp->ifsp;
+	else
+		mp->ifs = ' ';
+}
+
 /*
  * Perform parameter expansion, command substitution, and arithmetic
  * expansion on <str>.
@@ -167,10 +180,7 @@ char *sh_mactrim(char *str, int mode)
 		mp->assign = -mode;
 	mp->quoted = mp->lit = mp->split = mp->quote = 0;
 	mp->sp = 0;
-	if(mp->ifsp=nv_getval(sh_scoped(IFSNOD)))
-		mp->ifs = *mp->ifsp;
-	else
-		mp->ifs = ' ';
+	setup_ifs(mp);
 	stkseek(stkp,0);
 	fcsopen(str);
 	copyto(mp,0,mp->arith);
@@ -204,10 +214,7 @@ int sh_macexpand(struct argnod *argp, struct argnod **arghead,int flag)
 	Mac_t	savemac = *mp;
 	Stk_t	*stkp = sh.stk;
 	mp->sp = 0;
-	if(mp->ifsp=nv_getval(sh_scoped(IFSNOD)))
-		mp->ifs = *mp->ifsp;
-	else
-		mp->ifs = ' ';
+	setup_ifs(mp);
 	if((flag&ARG_OPTIMIZE) && !sh.indebug && !(flags&ARG_MESSAGE))
 		nv_setoptimize((char**)&argp->argchn.ap);
 	else
@@ -275,8 +282,7 @@ void sh_machere(Sfio_t *infile, Sfio_t *outfile, char *string)
 	mp->sp = outfile;
 	mp->split = mp->assign = mp->pattern = mp->patfound = mp->lit = mp->arith = 0;
 	mp->quote = 1;
-	mp->ifsp = nv_getval(sh_scoped(IFSNOD));
-	mp->ifs = ' ';
+	setup_ifs(mp);
 	fcsave(&save);
 	if(infile)
 		fcfopen(infile);

src/cmd/ksh93/tests/heredoc.sh

@@ -580,5 +580,26 @@ exp=$'\t\tTest line 1\n\tTest line 2'
 [[ $got == "$exp" ]] || err_exit "processing a here-document from a command substitution in a here-document" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
+# ======
+# $@ and $* in here-document
+# Note: POSIX sys that $@ has unspecified behaviour in this context because
+# field generation is not posible, but ksh's traditional behaviour is to pull
+# a space out of a hat and use it as the output field separator. Only $* makes
+# sense in a here-document. In any scalar context (in which field splittig is
+# not possible), POSIX specifies that $* uses the first character of $IFS as
+# the output field separator.
+got=$(
+	IFS=/
+	set ONE TWO THREE
+	cat <<-EOF
+		start$@end
+		start$*end
+	EOF
+)
+exp=$'startONE TWO THREEend\nstartONE/TWO/THREEend'
+[[ $got == "$exp" ]] || err_exit '$@ and $* in here-document' \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
+
 # ======
 exit $((Errors<125?Errors:125))