Early migration warning for editor-placeholder change

Author: Bromeon

godot-core/src/classes/class_runtime.rs

@@ -330,6 +330,7 @@ where
 /// Panic emitted when `bind()` / `bind_mut()` is called on a placeholder instance (runtime class accessed in the editor).
 #[track_caller]
 pub(crate) fn panic_placeholder_bind<T>(method: &str) -> ! {
+    crate::warn_editor_placeholder_v06!(id: "EditorPlaceholderV06Bind", surface: "Gd::bind/bind_mut");
     panic!(
         "Gd::{method}() called on a placeholder instance of `{name}`.\n\
         A non-tool class does not have a real instance in the editor.\n\

godot-core/src/private.rs

@@ -227,6 +227,39 @@ pub fn is_class_runtime(is_tool: bool) -> bool {
     global_config.tool_only_in_editor
 }
 
+/// Emits a one-shot startup warning when an editor code path is about to diverge from v0.6 default behavior.
+///
+/// Expands to a per-call-site `static Once` plus an `is_editor()` check, so each call site fires at most once.
+/// All ids share the `EditorPlaceholderV06` prefix and are individually suppressible via
+/// `GDRUST_SUPPRESSED_WARNINGS=<id>,...`.
+#[cfg(not(feature = "upcoming-editor-placeholders"))]
+#[macro_export]
+#[doc(hidden)]
+macro_rules! warn_editor_placeholder_v06 {
+    (id: $id:literal, surface: $surface:literal) => {{
+        static WARNED: std::sync::Once = std::sync::Once::new();
+        if $crate::sys::is_editor() {
+            WARNED.call_once(|| {
+                ::godot_ffi::defer_startup_warn!(
+                    id: $id,
+                    "godot-rust v0.6 will change editor behavior for non-`#[class(tool)]` runtime classes.\n\
+                    Your code currently relies on old behavior for {}.\n\
+                    Opt in early via the `upcoming-editor-placeholders` feature.",
+                    $surface,
+                );
+            });
+        }
+    }};
+}
+
+/// No-op stub when the feature is enabled, so call sites stay unconditional.
+#[cfg(feature = "upcoming-editor-placeholders")]
+#[macro_export]
+#[doc(hidden)]
+macro_rules! warn_editor_placeholder_v06 {
+    (id: $id:literal, surface: $surface:literal) => {{}};
+}
+
 /// Converts a default parameter value to a runtime-immutable `Variant`.
 ///
 /// This function is used internally by the `#[opt(default)]` attribute to:

godot-core/src/registry/callbacks.rs

@@ -214,6 +214,8 @@ pub unsafe extern "C" fn get_virtual<T: cap::ImplementsGodotVirtual>(
     name: sys::GDExtensionConstStringNamePtr,
     hash: u32,
 ) -> sys::GDExtensionClassCallVirtual {
+    crate::warn_editor_placeholder_v06!(id: "EditorPlaceholderV06Virtual", surface: "virtual callbacks (ready, notification, on_property_get_revert, ...)");
+
     unsafe {
         // This string is not ours, so we cannot call the destructor on it.
         let borrowed_string = StringName::borrow_string_sys(name);
@@ -228,6 +230,8 @@ pub unsafe extern "C" fn get_virtual<T: cap::ImplementsGodotVirtual>(
     _class_user_data: *mut std::ffi::c_void,
     name: sys::GDExtensionConstStringNamePtr,
 ) -> sys::GDExtensionClassCallVirtual {
+    crate::warn_editor_placeholder_v06!(id: "EditorPlaceholderV06Virtual", surface: "virtual callbacks (ready, notification, on_property_get_revert, ...)");
+
     // This string is not ours, so we cannot call the destructor on it.
     let borrowed_string = StringName::borrow_string_sys(name);
     let method_name = borrowed_string.to_string();
@@ -299,6 +303,8 @@ pub unsafe extern "C" fn get_property<T: cap::GodotGet>(
     name: sys::GDExtensionConstStringNamePtr,
     ret: sys::GDExtensionVariantPtr,
 ) -> sys::GDExtensionBool {
+    crate::warn_editor_placeholder_v06!(id: "EditorPlaceholderV06Property", surface: "#[var] accessors and IObject::on_get/on_set");
+
     unsafe {
         let storage = as_storage::<T>(instance);
         let instance = T::Recv::instance(storage);
@@ -319,6 +325,8 @@ pub unsafe extern "C" fn set_property<T: cap::GodotSet>(
     name: sys::GDExtensionConstStringNamePtr,
     value: sys::GDExtensionConstVariantPtr,
 ) -> sys::GDExtensionBool {
+    crate::warn_editor_placeholder_v06!(id: "EditorPlaceholderV06Property", surface: "#[var] accessors and IObject::on_get/on_set");
+
     unsafe {
         let storage = as_storage::<T>(instance);
         let instance = T::Recv::instance(storage);