[gimp] Add GError reporting to gimp_image_merge_down()

[Michael Natterer <mitch src gnome org>]

commit d37dc64b1628ea5ad4794b80c2a69240442c70c6
Author: Michael Natterer <mitch gimp org>
Date:   Tue Aug 25 22:02:02 2009 +0200

    Add GError reporting to gimp_image_merge_down()
    
    - turn g_return_if_fail() of more complex conditions into errors.
    - change PDB wrapper accordingly instead of adding a ton of conditions
      there.

 app/actions/layers-commands.c |    2 +-
 app/core/gimpimage-merge.c    |   34 ++++++++++++++++++++++++++--------
 app/core/gimpimage-merge.h    |    3 ++-
 app/pdb/image-cmds.c          |   10 ++++++++--
 tools/pdbgen/pdb/image.pdb    |   10 ++++++++--
 5 files changed, 45 insertions(+), 14 deletions(-)
---
diff --git a/app/actions/layers-commands.c b/app/actions/layers-commands.c
index 2499aac..5236eee 100644
--- a/app/actions/layers-commands.c
+++ b/app/actions/layers-commands.c
@@ -501,7 +501,7 @@ layers_merge_down_cmd_callback (GtkAction *action,
   return_if_no_layer (image, layer, data);
 
   gimp_image_merge_down (image, layer, action_data_get_context (data),
-                         GIMP_EXPAND_AS_NECESSARY);
+                         GIMP_EXPAND_AS_NECESSARY, NULL);
   gimp_image_flush (image);
 }
 
diff --git a/app/core/gimpimage-merge.c b/app/core/gimpimage-merge.c
index e293b25..2d06c22 100644
--- a/app/core/gimpimage-merge.c
+++ b/app/core/gimpimage-merge.c
@@ -174,10 +174,11 @@ gimp_image_flatten (GimpImage   *image,
 }
 
 GimpLayer *
-gimp_image_merge_down (GimpImage     *image,
-                       GimpLayer     *current_layer,
-                       GimpContext   *context,
-                       GimpMergeType  merge_type)
+gimp_image_merge_down (GimpImage      *image,
+                       GimpLayer      *current_layer,
+                       GimpContext    *context,
+                       GimpMergeType   merge_type,
+                       GError        **error)
 {
   GimpLayer *layer;
   GList     *list;
@@ -187,9 +188,15 @@ gimp_image_merge_down (GimpImage     *image,
   g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
   g_return_val_if_fail (GIMP_IS_LAYER (current_layer), NULL);
   g_return_val_if_fail (gimp_item_is_attached (GIMP_ITEM (current_layer)), NULL);
-  g_return_val_if_fail (gimp_viewable_get_children (GIMP_VIEWABLE (current_layer)) == NULL,
-                        NULL);
   g_return_val_if_fail (GIMP_IS_CONTEXT (context), NULL);
+  g_return_val_if_fail (error == NULL || *error == NULL, NULL);
+
+  if (gimp_viewable_get_children (GIMP_VIEWABLE (current_layer)))
+    {
+      g_set_error_literal (error, 0, 0,
+                           _("Cannot merge down a group layer."));
+      return NULL;
+    }
 
   for (list = gimp_item_get_container_iter (GIMP_ITEM (current_layer));
        list;
@@ -209,14 +216,25 @@ gimp_image_merge_down (GimpImage     *image,
 
       if (gimp_item_get_visible (GIMP_ITEM (layer)))
         {
-          g_return_val_if_fail (! gimp_item_get_lock_content (GIMP_ITEM (layer)),
-                                NULL);
+          if (gimp_item_get_lock_content (GIMP_ITEM (layer)))
+            {
+              g_set_error_literal (error, 0, 0,
+                                   _("The layer to merge down to is locked."));
+              return NULL;
+            }
 
           merge_list = g_slist_append (NULL, layer);
           break;
         }
     }
 
+  if (! merge_list)
+    {
+      g_set_error_literal (error, 0, 0,
+                           _("There is no visible layer to merge down to."));
+      return NULL;
+    }
+
   merge_list = g_slist_prepend (merge_list, current_layer);
 
   gimp_set_busy (image->gimp);
diff --git a/app/core/gimpimage-merge.h b/app/core/gimpimage-merge.h
index fe290b2..32a3779 100644
--- a/app/core/gimpimage-merge.h
+++ b/app/core/gimpimage-merge.h
@@ -26,7 +26,8 @@ GimpLayer   * gimp_image_merge_visible_layers  (GimpImage      *image,
 GimpLayer   * gimp_image_merge_down            (GimpImage      *image,
                                                 GimpLayer      *current_layer,
                                                 GimpContext    *context,
-                                                GimpMergeType   merge_type);
+                                                GimpMergeType   merge_type,
+                                                GError        **error);
 GimpLayer   * gimp_image_flatten               (GimpImage      *image,
                                                 GimpContext    *context);
 GimpVectors * gimp_image_merge_visible_vectors (GimpImage      *image,
diff --git a/app/pdb/image-cmds.c b/app/pdb/image-cmds.c
index e0c123c..610b6ba 100644
--- a/app/pdb/image-cmds.c
+++ b/app/pdb/image-cmds.c
@@ -1508,9 +1508,15 @@ image_merge_down_invoker (GimpProcedure      *procedure,
 
   if (success)
     {
-      layer = gimp_image_merge_down (image, merge_layer, context, merge_type);
+      if (gimp_pdb_item_is_attached (GIMP_ITEM (merge_layer), FALSE, error))
+        {
+          layer = gimp_image_merge_down (image, merge_layer, context, merge_type,
+                                         error);
 
-      if (! layer)
+          if (! layer)
+            success = FALSE;
+        }
+      else
         success = FALSE;
     }
 
diff --git a/tools/pdbgen/pdb/image.pdb b/tools/pdbgen/pdb/image.pdb
index 8585db2..3e4eba8 100644
--- a/tools/pdbgen/pdb/image.pdb
+++ b/tools/pdbgen/pdb/image.pdb
@@ -941,9 +941,15 @@ HELP
 	headers => [ qw("core/gimpimage-merge.h") ],
 	code => <<'CODE'
 {
-  layer = gimp_image_merge_down (image, merge_layer, context, merge_type);
+  if (gimp_pdb_item_is_attached (GIMP_ITEM (merge_layer), FALSE, error))
+    {
+      layer = gimp_image_merge_down (image, merge_layer, context, merge_type,
+                                     error);
 
-  if (! layer)
+      if (! layer)
+        success = FALSE;
+    }
+  else
     success = FALSE;
 }
 CODE