Nodes: support optional labels for group inputs

Built-in nodes already used the functionality to hide the input labels in a few
situations. However, this functionality was not exposed for node groups before.
It required some refactoring to get the semantics of the flag right. The tricky
aspect is that "Hide Label" would be an incorrect name, because the label is
still shown under various circumstances. Instead, the flag merely indicates that
drawing code may skip drawing the label.

This adds a new "Optional Label" input for node group inputs. Other names are
possible like "Requires Label" which would be the inverse.

Overall the implementation is pretty straight forward after
1f489ea31a,
469a70dba9 and
f79896f5b9.

Pull Request: https://projects.blender.org/blender/blender/pulls/146939

source/blender/blenkernel/intern/node_tree_interface.cc

@@ -1156,6 +1156,7 @@ bNodeTreeInterfaceSocket *add_interface_socket_from_node(bNodeTree &ntree,
       if (!decl->description.empty()) {
         description = decl->description;
       }
+      SET_FLAG_FROM_TEST(flag, decl->optional_label, NODE_INTERFACE_SOCKET_OPTIONAL_LABEL);
     }
 
     iosock = ntree.tree_interface.add_socket(name, description, socket_type, flag, nullptr);

source/blender/editors/space_node/drawnode.cc

@@ -1420,6 +1420,9 @@ static void std_node_socket_interface_draw(ID *id,
     }
   }
 
+  if (interface_socket->flag & NODE_INTERFACE_SOCKET_INPUT) {
+    col->prop(&ptr, "optional_label", DEFAULT_FLAGS, std::nullopt, ICON_NONE);
+  }
   {
     uiLayout *sub = &col->column(false);
     sub->active_set(interface_socket->default_input == NODE_DEFAULT_INPUT_VALUE);

source/blender/makesdna/DNA_node_tree_interface_types.h

@@ -70,8 +70,13 @@ typedef enum NodeTreeInterfaceSocketFlag {
   NODE_INTERFACE_SOCKET_PANEL_TOGGLE = 1 << 8,
   /* Menu socket should be drawn expanded instead of as drop-down menu. */
   NODE_INTERFACE_SOCKET_MENU_EXPANDED = 1 << 9,
+  /**
+   * Indicates that drawing code may decide not to draw the label if that would result in a
+   * cleaner UI.
+   */
+  NODE_INTERFACE_SOCKET_OPTIONAL_LABEL = 1 << 10,
 } NodeTreeInterfaceSocketFlag;
-ENUM_OPERATORS(NodeTreeInterfaceSocketFlag, NODE_INTERFACE_SOCKET_MENU_EXPANDED);
+ENUM_OPERATORS(NodeTreeInterfaceSocketFlag, NODE_INTERFACE_SOCKET_OPTIONAL_LABEL);
 
 typedef enum NodeSocketInterfaceStructureType {
   NODE_INTERFACE_SOCKET_STRUCTURE_TYPE_AUTO = 0,

source/blender/makesrna/intern/rna_node_tree_interface.cc

@@ -1205,6 +1205,16 @@ static void rna_def_node_interface_socket(BlenderRNA *brna)
       prop, "Menu Expanded", "Draw the menu socket as an expanded drop-down menu");
   RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_NodeTreeInterfaceItem_update");
 
+  prop = RNA_def_property(srna, "optional_label", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, nullptr, "flag", NODE_INTERFACE_SOCKET_OPTIONAL_LABEL);
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_ui_text(
+      prop,
+      "Optional Label",
+      "Indicate that the label of this socket is not necessary to understand its meaning. This "
+      "may result in the label being skipped in some cases");
+  RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_NodeTreeInterfaceItem_update");
+
   prop = RNA_def_property(srna, "attribute_domain", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_items(prop, rna_enum_attribute_domain_items);
   RNA_def_property_enum_funcs(

source/blender/nodes/intern/node_common.cc

@@ -393,6 +393,7 @@ static BaseSocketDeclarationBuilder &build_interface_socket_declaration(
   decl->hide_value(io_socket.flag & NODE_INTERFACE_SOCKET_HIDE_VALUE);
   decl->compact(io_socket.flag & NODE_INTERFACE_SOCKET_COMPACT);
   decl->panel_toggle(io_socket.flag & NODE_INTERFACE_SOCKET_PANEL_TOGGLE);
+  decl->optional_label(io_socket.flag & NODE_INTERFACE_SOCKET_OPTIONAL_LABEL);
   decl->default_input_type(NodeDefaultInputType(io_socket.default_input));
   if (structure_type) {
     decl->structure_type(*structure_type);