54674: ::= didn't respect parameter flags

The documentation says
    ${name::=word}
          In  the first form, if name is unset then set it to word; in
          the second form, if name is unset or null then set it to word;
          and in the third form, unconditionally  set name to word.  In
          all forms, the value of the parameter is then substituted.

Particularly that "the value of the parameter is substituted", not "the
word is substituted".

This is what happens before the fix, and similarly for array flags like "unique":

% typeset -E3 fl; hi=5; echo ${fl::=hi}
hi
% echo $fl
5.00e+00

1 files changed, 13 insertions, 3 deletions

diff --git a/Src/subst.c b/Src/subst.c
index 16a3cb055..f72a6baf2 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -3300,13 +3300,23 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 			Param pm = sethparam(idbeg, a);
 			if (pm)
 			    aval = paramvalarr(pm->gsu.h->getfn(pm), hkeys|hvals);
-		    } else
-			setaparam(idbeg, a);
+		    } else {
+			Param pm = setaparam(idbeg, a);
+			if (pm)
+			    aval = pm->gsu.a->getfn(pm);
+		    }
 		    isarr = 1;
 		    arrasg = 0;
 		} else {
 		    untokenize(val);
-		    setsparam(idbeg, ztrdup(val));
+		    Param pm = setsparam(idbeg, ztrdup(val));
+		    if (pm) {
+			struct value vbuf = { 0 };
+			vbuf.pm = pm;
+			vbuf.end = -1;
+			vbuf.valflags = VALFLAG_SUBST;
+			val = getstrvalue(&vbuf);
+		    }
 		}
 		*idend = sav;
 		copied = 1;