Geometry Nodes: initial attribute list for meshes

This adds a new Attributes panel in the mesh properties editor.
It shows a list of all the generic attributes on the mesh.
In the future, we want to show built-in and other attributes in the
list as well. Related technical design tasks: T88460, T89054.

There is also a new simple name collision check that warns the user
when there are multiple attributes with the same name. This can be
problematic when the attribute is supposed to be used in geometry
nodes or during rendering.

Differential Revision: https://developer.blender.org/D11276

release/scripts/startup/bl_ui/properties_data_mesh.py

@@ -20,6 +20,7 @@
 import bpy
 from bpy.types import Menu, Panel, UIList
 from rna_prop_ui import PropertyPanel
+from collections import defaultdict
 
 
 class MESH_MT_vertex_group_context_menu(Menu):
@@ -566,6 +567,89 @@ class DATA_PT_custom_props_mesh(MeshButtonsPanel, PropertyPanel, Panel):
     _property_type = bpy.types.Mesh
 
 
+class MESH_UL_attributes(UIList):
+    display_domain_names = {
+        'POINT': "Vertex",
+        'EDGE': "Edge",
+        'FACE': "Face",
+        'CORNER': "Face Corner",
+    }
+
+    def draw_item(self, _context, layout, _data, attribute, _icon, _active_data, _active_propname, _index):
+        data_type = attribute.bl_rna.properties['data_type'].enum_items[attribute.data_type]
+
+        domain_name = self.display_domain_names.get(attribute.domain, "")
+
+        split = layout.split(factor=0.50)
+        split.emboss = 'NONE'
+        split.prop(attribute, "name", text="")
+        sub = split.row()
+        sub.alignment = 'RIGHT'
+        sub.active = False
+        sub.label(text="%s ▶ %s" % (domain_name, data_type.name))
+
+
+class DATA_PT_mesh_attributes(MeshButtonsPanel, Panel):
+    bl_label = "Attributes"
+    bl_options = {'DEFAULT_CLOSED'}
+    COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_EEVEE', 'BLENDER_WORKBENCH'}
+
+    def draw(self, context):
+        mesh = context.mesh
+
+        layout = self.layout
+        row = layout.row()
+
+        col = row.column()
+        col.template_list(
+            "MESH_UL_attributes",
+            "attributes",
+            mesh,
+            "attributes",
+            mesh.attributes,
+            "active_index",
+            rows=3,
+        )
+
+        col = row.column(align=True)
+        col.operator("geometry.attribute_add", icon='ADD', text="")
+        col.operator("geometry.attribute_remove", icon='REMOVE', text="")
+
+        self.draw_attribute_warnings(context, layout)
+
+    def draw_attribute_warnings(self, context, layout):
+        attributes_by_name = defaultdict(list)
+
+        ob = context.object
+        mesh = ob.data
+
+        builtin_attribute = object()
+
+        def add_builtin(name):
+            attributes_by_name[name].append(builtin_attribute)
+
+        def add_attributes(layers):
+            for layer in layers:
+                attributes_by_name[layer.name].append(layer)
+
+        add_builtin("position")
+        add_builtin("material_index")
+        add_builtin("shade_smooth")
+        add_builtin("normal")
+        add_builtin("crease")
+
+        add_attributes(mesh.attributes)
+        add_attributes(mesh.uv_layers)
+        add_attributes(mesh.vertex_colors)
+        add_attributes(ob.vertex_groups)
+
+        colliding_names = [name for name, layers in attributes_by_name.items() if len(layers) >= 2]
+        if len(colliding_names) == 0:
+            return
+
+        layout.label(text="Name Collisions: {}".format(", ".join(colliding_names)), icon='INFO')
+
+
 classes = (
     MESH_MT_vertex_group_context_menu,
     MESH_MT_shape_key_context_menu,
@@ -574,6 +658,7 @@ classes = (
     MESH_UL_shape_keys,
     MESH_UL_uvmaps,
     MESH_UL_vcols,
+    MESH_UL_attributes,
     DATA_PT_context_mesh,
     DATA_PT_vertex_groups,
     DATA_PT_shape_keys,
@@ -581,6 +666,7 @@ classes = (
     DATA_PT_vertex_colors,
     DATA_PT_sculpt_vertex_colors,
     DATA_PT_face_maps,
+    DATA_PT_mesh_attributes,
     DATA_PT_normals,
     DATA_PT_texture_space,
     DATA_PT_remesh,