hush: fix quoted "${notexist-}" expansion to not disappear

function                                             old     new   delta
expand_one_var                                      2296    2311     +15

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-vars/param_expand_default.right

@@ -5,3 +5,5 @@ _aaaa _aaaa _aaaa _aaaa _aaaa
 _ _ _ _word _word
 _ _ _ _ _word
 _fff _fff _fff _fff _fff
+1:1
+0:0

shell/ash_test/ash-vars/param_expand_default.tests

@@ -21,3 +21,8 @@ echo _$f _${f-} _${f:-} _${f-word} _${f:-word}
 
 f=fff
 echo _$f _${f-} _${f:-} _${f-word} _${f:-word}
+
+set --
+set -- "${1-}"; echo 1:$#
+set --
+set -- ${1-}; echo 0:$#

shell/hush.c

@@ -6132,6 +6132,12 @@ static int encode_then_append_var_plusminus(o_string *output, int n,
 		/* string has no special chars
 		 * && string has no $IFS chars
 		 */
+		if (dquoted) {
+			/* Prints 1 (quoted expansion is a "" word, not nothing):
+			 * set -- "${notexist-}"; echo $#
+			 */
+			output->has_quoted_part = 1;
+		}
 		return expand_vars_to_list(output, n, str);
 	}
 

shell/hush_test/hush-vars/param_expand_default.right

@@ -6,3 +6,5 @@ _aaaa _aaaa _aaaa _aaaa _aaaa
 _ _ _ _word _word
 _ _ _ _ _word
 _fff _fff _fff _fff _fff
+1:1
+0:0

shell/hush_test/hush-vars/param_expand_default.tests

@@ -22,3 +22,8 @@ echo _$f _${f-} _${f:-} _${f-word} _${f:-word}
 
 f=fff
 echo _$f _${f-} _${f:-} _${f-word} _${f:-word}
+
+set --
+set -- "${1-}"; echo 1:$#
+set --
+set -- ${1-}; echo 0:$#