string-output-visitor: Support lists for non-integer types

With the introduction of list-based array properties in qdev, the string
output visitor has to deal with lists of non-integer elements now ('info
qtree' prints all properties with the string output visitor).

Currently there is no explicit support for such lists, and the resulting
output is only the last element because string_output_set() always
replaces the output with the latest value. Instead of replacing the old
value, append comma separated values in list context.

The difference can be observed in 'info qtree' with a 'rocker' device
that has a 'ports' list with more than one element.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20231121173416.346610-3-kwolf@redhat.com>

qapi/string-output-visitor.c

@@ -74,11 +74,27 @@ static StringOutputVisitor *to_sov(Visitor *v)
 
 static void string_output_set(StringOutputVisitor *sov, char *string)
 {
-    if (sov->string) {
-        g_string_free(sov->string, true);
+    switch (sov->list_mode) {
+    case LM_STARTED:
+        sov->list_mode = LM_IN_PROGRESS;
+        /* fall through */
+    case LM_NONE:
+        if (sov->string) {
+            g_string_free(sov->string, true);
+        }
+        sov->string = g_string_new(string);
+        g_free(string);
+        break;
+
+    case LM_IN_PROGRESS:
+    case LM_END:
+        g_string_append(sov->string, ", ");
+        g_string_append(sov->string, string);
+        break;
+
+    default:
+        abort();
     }
-    sov->string = g_string_new(string);
-    g_free(string);
 }
 
 static void string_output_append(StringOutputVisitor *sov, int64_t a)