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difference between ${...=...} and ${...+...} with (j:_:)

While looking at the multsub() code, I noticed something that may be

    % foo=(1 2 3)
    % unset ick; echo ${(j:_:)ick=$foo}
    1 2 3
    % echo ${(j:_:)ick+$foo}

Now, the first case makes sense to me because the joined value of $foo
gets assigned to $ick, and the 'j' flag applies to that variable (doing
nothing).  The latter looks like a mistake, since $foo should get joined
with the normal IFS char (since it is not the object of the 'j' flag).
I would assume that the user should apply the 'j' flag directly to the
array variable to get joining (both of which works right):

    % foo=(1 2 3)
    % unset ick; echo ${ick=${(j:_:)foo}}
    % echo ${ick+${(j:_:)foo}}

Is this an inconsistency?  Or a misunderstanding on my part?

I'm also keen to change is the unused arg sent to multsub().  Currently
the comment prior to the function says that it honors the sep arg when
joining arrays, but it doesn't really.  Since it appears we don't need
it, should we remove it?  I chose to re-active it, and just make all the
current callers pass a NULL.

Another thing I saw was some useless code in multsub() that checks if
"l" is non-zero where it can't possibly be anything but 0.  I thought at
first that the "if ((l = countlinknodes(&foo)))" check should be changed
into "if ((l = countlinknodes(&foo)) > 1)", but it appears that some
callers like to receive a 1-element array (fortunately, one of the test
cases depends on this).  So, I'd suggest that we change that line to be
"if ((l = countlinknodes(&foo)) > (a ? 0 : 1))", since this just avoids
creating a one-element array if we're going to join it into a scalar
(because the caller didn't give us a way to return an array).

Attached is a patch that optimizes multsub(), makes its "sep" arg work
again (though no callers currently use it), fixes the inconsistency
mentioned at the start of this message, and gets rid of a superfluous
"isarr = 0" assignment (due to both of the following multsub() calls
now passing in &isarr).

This seems safe enough to check in (assuming that item #1 needs to be

--- Src/subst.c	6 Feb 2006 11:57:06 -0000	1.44
+++ Src/subst.c	13 Feb 2006 07:35:53 -0000
@@ -310,7 +310,7 @@ static int mult_isarr;
 static int
-multsub(char **s, char ***a, int *isarr, UNUSED(char *sep))
+multsub(char **s, char ***a, int *isarr, char *sep)
     int l, omi = mult_isarr;
     char **r, **p;
@@ -325,7 +325,7 @@ multsub(char **s, char ***a, int *isarr,
 	mult_isarr = omi;
 	return 0;
-    if ((l = countlinknodes(&foo))) {
+    if ((l = countlinknodes(&foo)) > (a ? 0 : 1)) {
 	p = r = hcalloc((l + 1) * sizeof(char*));
 	while (nonempty(&foo))
 	    *p++ = (char *)ugetnode(&foo);
@@ -345,7 +345,7 @@ multsub(char **s, char ***a, int *isarr,
 	    mult_isarr = omi;
 	    return 0;
-	*s = sepjoin(r, NULL, 1);
+	*s = sepjoin(r, sep, 1);
 	mult_isarr = omi;
 	if (isarr)
 	    *isarr = 0;
@@ -2012,6 +2012,7 @@ paramsubst(LinkList l, LinkNode n, char 
 		multsub(&val, (aspar ? NULL : &aval), &isarr, NULL);
 		copied = 1;
+		sep = NULL;
 	case ':':
@@ -2029,7 +2030,6 @@ paramsubst(LinkList l, LinkNode n, char 
 		*idend = '\0';
 		val = dupstring(s);
-		isarr = 0;
 		 * TODO: this is one of those places where I don't
 		 * think we want to do the joining until later on.
@@ -2037,7 +2037,7 @@ paramsubst(LinkList l, LinkNode n, char 
 		 * point and unset them.
 		if (spsep || spbreak || !arrasg)
-		    multsub(&val, NULL, NULL, sep);
+		    multsub(&val, NULL, &isarr, NULL);
 		    multsub(&val, &aval, &isarr, NULL);
 		if (arrasg) {

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