Outliner: Refactor element warning and mode column querying

Uses a inheritance based approach for querying warning of tree elements
and the mode column support of display modes.

For the warnings, tree elements can override the
`AbstractTreeElement::getWarning()` method and return a warning string.
The UI will draw the warning column with warning icons. This makes the
warning column more generalized and easier to extend to more use-cases.
E.g. library override elements will use this after a followup commit.

To support mode toggles a display mode can now just return true in the
`AbstractTreeDisplay::supportsModeColumn()` method. This makes it
trivial to add mode columns to other display modes, and less error prone
because there's no need to hunt down a bunch of display mode checks in
different places.

1 files changed, 8 insertions, 9 deletions

diff --git a/source/blender/editors/space_outliner/tree/tree_element.hh b/source/blender/editors/space_outliner/tree/tree_element.hh
index c6593a517dd..d665ff49f53 100644
--- a/source/blender/editors/space_outliner/tree/tree_element.hh
+++ b/source/blender/editors/space_outliner/tree/tree_element.hh
@@ -8,6 +8,8 @@
 
 #include <memory>
 
+#include "BLI_string_ref.hh"
+
 struct ListBase;
 struct SpaceOutliner;
 struct TreeElement;
@@ -56,6 +58,12 @@ class AbstractTreeElement {
   }
 
   /**
+   * By letting this return a warning message, the tree element will display a warning icon with
+   * the message in the tooltip.
+   */
+  virtual blender::StringRefNull getWarning() const;
+
+  /**
    * Expand this tree element if it is displayed for the first time (as identified by its
    * tree-store element).
    *
@@ -96,13 +104,4 @@ struct TreeElement *outliner_add_element(SpaceOutliner *space_outliner,
 
 void tree_element_expand(const AbstractTreeElement &tree_element, SpaceOutliner &space_outliner);
 
-/**
- * Get actual warning data of a tree element, if any.
- *
- * \param r_icon: The icon to display as warning.
- * \param r_message: The message to display as warning.
- * \return true if there is a warning, false otherwise.
- */
-bool tree_element_warnings_get(struct TreeElement *te, int *r_icon, const char **r_message);
-
 }  // namespace blender::ed::outliner