From b1d02f9323d4eb157dc99e0b7a79d06a2e510500 Mon Sep 17 00:00:00 2001
From: Ryan Lortie <desrt@desrt.ca>
Date: Fri, 11 Feb 2011 10:14:29 -0500
Subject: [PATCH] GVariant: support NULL for empty arrays in varargs

g_variant_new("as", NULL); now gives an empty array of strings, for
example.

This was documented as working already, but was never actually
implemented (due to the fact that it muddies the water when considering
maybe types).  It's being implemented now because its convenience to
programmers exceeds any damage done to the conceptual purity of the API.
---
 docs/reference/glib/gvariant-varargs.xml |  5 +++
 glib/gvariant.c                          | 52 ++++++++++++++++--------
 glib/tests/gvariant.c                    | 16 ++++++++
 3 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/docs/reference/glib/gvariant-varargs.xml b/docs/reference/glib/gvariant-varargs.xml
index 334285988..8e87cde58 100644
--- a/docs/reference/glib/gvariant-varargs.xml
+++ b/docs/reference/glib/gvariant-varargs.xml
@@ -681,6 +681,11 @@ g_variant_unref (value);]]></programlisting></informalexample>
     prefixed with an '<literal>m</literal>', the type of arguments that are collected does not change in any way, but
     <link linkend='NULL--CAPS'><literal>NULL</literal></link> becomes a permissable value, to indicate the Nothing case.
    </para>
+   <para>
+    Note that the "special exception" introduced in the array section for constructing empty arrays is ignored
+    here.  Using a <literal>NULL</literal> pointer with the format string '<literal>mas</literal>' constructs
+    the Nothing value -- not an empty array.
+   </para>
    <para>
     The second way is used with all other format strings.  For
     <link linkend='g-variant-new'><function>g_variant_new()</function></link> an additional
diff --git a/glib/gvariant.c b/glib/gvariant.c
index 33bae0354..6bfc9007d 100644
--- a/glib/gvariant.c
+++ b/glib/gvariant.c
@@ -3643,30 +3643,46 @@ g_variant_valist_new_nnp (const gchar **str,
   switch (*(*str)++)
     {
     case 'a':
-      {
-        const GVariantType *type;
-        GVariant *value;
+      if (ptr != NULL)
+        {
+          const GVariantType *type;
+          GVariant *value;
 
-        value = g_variant_builder_end (ptr);
-        type = g_variant_get_type (value);
+          value = g_variant_builder_end (ptr);
+          type = g_variant_get_type (value);
 
-        if G_UNLIKELY (!g_variant_type_is_array (type))
-          g_error ("g_variant_new: expected array GVariantBuilder but "
-                   "the built value has type `%s'",
-                   g_variant_get_type_string (value));
+          if G_UNLIKELY (!g_variant_type_is_array (type))
+            g_error ("g_variant_new: expected array GVariantBuilder but "
+                     "the built value has type `%s'",
+                     g_variant_get_type_string (value));
 
-        type = g_variant_type_element (type);
+          type = g_variant_type_element (type);
 
-        if G_UNLIKELY (!g_variant_type_is_subtype_of (type, (GVariantType *) *str))
-          g_error ("g_variant_new: expected GVariantBuilder array element "
-                   "type `%s' but the built value has element type `%s'",
-                   g_variant_type_dup_string ((GVariantType *) *str),
-                   g_variant_get_type_string (value) + 1);
+          if G_UNLIKELY (!g_variant_type_is_subtype_of (type, (GVariantType *) *str))
+            g_error ("g_variant_new: expected GVariantBuilder array element "
+                     "type `%s' but the built value has element type `%s'",
+                     g_variant_type_dup_string ((GVariantType *) *str),
+                     g_variant_get_type_string (value) + 1);
 
-        g_variant_type_string_scan (*str, NULL, str);
+          g_variant_type_string_scan (*str, NULL, str);
 
-        return value;
-      }
+          return value;
+        }
+      else
+
+        /* special case: NULL pointer for empty array */
+        {
+          const GVariantType *type = (GVariantType *) *str;
+
+          g_variant_type_string_scan (*str, NULL, str);
+
+          if G_UNLIKELY (!g_variant_type_is_definite (type))
+            g_error ("g_variant_new: NULL pointer given with indefinite "
+                     "array type; unable to determine which type of empty "
+                     "array to construct.");
+
+          return g_variant_new_array (type, NULL, 0);
+        }
 
     case 's':
       return g_variant_new_string (ptr);
diff --git a/glib/tests/gvariant.c b/glib/tests/gvariant.c
index afbafd4e3..7fc96e59f 100644
--- a/glib/tests/gvariant.c
+++ b/glib/tests/gvariant.c
@@ -3331,6 +3331,22 @@ test_varargs (void)
     g_variant_unref (value);
   }
 
+  {
+    GVariant *value;
+    gchar *str;
+
+    value = g_variant_new ("(masas)", NULL, NULL);
+    g_variant_ref_sink (value);
+
+    str = g_variant_print (value, TRUE);
+    g_assert_cmpstr (str, ==, "(@mas nothing, @as [])");
+    g_variant_unref (value);
+    g_free (str);
+
+    if (do_failed_test ("*which type of empty array*"))
+      g_variant_new ("(a{s*})", NULL);
+  }
+
   g_variant_type_info_assert_no_infos ();
 }