[pygobject] cairo: Fix GValue converters in case it contains NULL

[Christoph Reiter <creiter src gnome org>]

commit c6ef6bafe795a4a4ac5dd72eb11c433a1e107af1
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Sat Nov 24 21:36:21 2018 +0100

    cairo: Fix GValue converters in case it contains NULL
    
    The default values for the cairo boxed types is NULL and the converters
    incorrectly returned NULL instead of a None object.
    Also add tests for all of them.

 gi/pygi-foreign-cairo.c | 10 +++++-----
 tests/test_cairo.py     | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+), 5 deletions(-)
---
diff --git a/gi/pygi-foreign-cairo.c b/gi/pygi-foreign-cairo.c
index 718f9a0f..c99847bf 100644
--- a/gi/pygi-foreign-cairo.c
+++ b/gi/pygi-foreign-cairo.c
@@ -118,7 +118,7 @@ cairo_context_from_gvalue (const GValue *value)
     /* PycairoContext_FromContext steals a ref, so we dup it out of the GValue. */
     cairo_t *cr = g_value_dup_boxed (value);
     if (!cr) {
-        return NULL;
+        Py_RETURN_NONE;
     }
 
     return PycairoContext_FromContext (cr, &PycairoContext_Type, NULL);
@@ -203,7 +203,7 @@ cairo_surface_from_gvalue (const GValue *value)
     /* PycairoSurface_FromSurface steals a ref, so we dup it out of the GValue. */
     cairo_surface_t *surface = g_value_dup_boxed (value);
     if (!surface) {
-        return NULL;
+        Py_RETURN_NONE;
     }
 
     return PycairoSurface_FromSurface (surface, NULL);
@@ -308,7 +308,7 @@ cairo_font_face_from_gvalue (const GValue *value)
 {
     cairo_font_face_t *font_face = g_value_dup_boxed (value);
     if (!font_face) {
-        return NULL;
+        Py_RETURN_NONE;
     }
 
     return PycairoFontFace_FromFontFace (font_face);
@@ -398,7 +398,7 @@ cairo_scaled_font_from_gvalue (const GValue *value)
     /* PycairoScaledFont_FromScaledFont steals a ref, so we dup it out of the GValue. */
     cairo_scaled_font_t *scaled_font = g_value_dup_boxed (value);
     if (!scaled_font) {
-        return NULL;
+        Py_RETURN_NONE;
     }
 
     return PycairoScaledFont_FromScaledFont (scaled_font);
@@ -436,7 +436,7 @@ cairo_pattern_from_gvalue (const GValue *value)
     /* PycairoPattern_FromPattern steals a ref, so we dup it out of the GValue. */
     cairo_pattern_t *pattern = g_value_dup_boxed (value);
     if (!pattern) {
-        return NULL;
+        Py_RETURN_NONE;
     }
 
     return PycairoPattern_FromPattern (pattern, NULL);
diff --git a/tests/test_cairo.py b/tests/test_cairo.py
index 8ccbe15a..f4d0d7c9 100644
--- a/tests/test_cairo.py
+++ b/tests/test_cairo.py
@@ -30,6 +30,27 @@ from gi.repository import GObject, Regress
 
 @unittest.skipUnless(has_cairo, 'built without cairo support')
 class Test(unittest.TestCase):
+
+    def test_gvalue_converters(self):
+        surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 10, 10)
+        context = cairo.Context(surface)
+        objects = {
+            'CairoContext': context,
+            'CairoSurface': surface,
+            'CairoFontFace': context.get_font_face(),
+            'CairoScaledFont': context.get_scaled_font(),
+            'CairoPattern': context.get_source(),
+        }
+        for type_name, cairo_obj in objects.items():
+            gtype = GObject.type_from_name(type_name)
+            v = GObject.Value()
+            assert v.init(gtype) is None
+            assert v.get_value() is None
+            v.set_value(None)
+            assert v.get_value() is None
+            v.set_value(cairo_obj)
+            assert v.get_value() == cairo_obj
+
     def test_cairo_context(self):
         context = Regress.test_cairo_context_full_return()
         self.assertTrue(isinstance(context, cairo.Context))