Handle panic in OnReady auto_init.

Author: Yarwin

godot-core/src/obj/on_ready.rs

@@ -207,13 +207,9 @@ impl<T> OnReady<T> {
             InitState::ManualUninitialized => {
                 self.state = InitState::Initialized { value };
             }
-            InitState::AutoPrepared { .. } => {
+            InitState::AutoPrepared { .. } | InitState::AutoInitializationFailed => {
                 panic!("cannot call init() on auto-initialized OnReady objects")
             }
-            InitState::AutoInitializing => {
-                // SAFETY: Loading is ephemeral state that is only set in init_auto() and immediately overwritten.
-                unsafe { std::hint::unreachable_unchecked() }
-            }
             InitState::Initialized { .. } => {
                 panic!("already initialized; did you call init() more than once?")
             }
@@ -223,22 +219,22 @@ impl<T> OnReady<T> {
     /// Runs initialization.
     ///
     /// # Panics
-    /// If the value is already initialized.
+    /// - If the value is already initialized.
+    /// - If previous auto initialization failed.
     pub(crate) fn init_auto(&mut self, base: &Gd<Node>) {
         // Two branches needed, because mem::replace() could accidentally overwrite an already initialized value.
         match &self.state {
             InitState::ManualUninitialized => return, // skipped
             InitState::AutoPrepared { .. } => {}      // handled below
-            InitState::AutoInitializing => {
-                // SAFETY: Loading is ephemeral state that is only set below and immediately overwritten.
-                unsafe { std::hint::unreachable_unchecked() }
+            InitState::AutoInitializationFailed => {
+                panic!("OnReady automatic value initialization has already failed")
             }
             InitState::Initialized { .. } => panic!("OnReady object already initialized"),
         };
 
-        // Temporarily replace with dummy state, as it's not possible to take ownership of the initializer closure otherwise.
+        // Temporally replace with AutoInitializationFailed state which will be left in iff initialization fails.
         let InitState::AutoPrepared { initializer } =
-            mem::replace(&mut self.state, InitState::AutoInitializing)
+            mem::replace(&mut self.state, InitState::AutoInitializationFailed)
         else {
             // SAFETY: condition checked above.
             unsafe { std::hint::unreachable_unchecked() }
@@ -267,7 +263,9 @@ impl<T> std::ops::Deref for OnReady<T> {
             InitState::AutoPrepared { .. } => {
                 panic!("OnReady automatic value uninitialized, is only available in ready()")
             }
-            InitState::AutoInitializing => unreachable!(),
+            InitState::AutoInitializationFailed => {
+                panic!("OnReady automatic value initialization failed")
+            }
             InitState::Initialized { value } => value,
         }
     }
@@ -284,7 +282,9 @@ impl<T> std::ops::DerefMut for OnReady<T> {
             InitState::ManualUninitialized | InitState::AutoPrepared { .. } => {
                 panic!("value not yet initialized")
             }
-            InitState::AutoInitializing => unreachable!(),
+            InitState::AutoInitializationFailed => {
+                panic!("OnReady automatic value initialization failed")
+            }
         }
     }
 }
@@ -313,7 +313,7 @@ type InitFn<T> = dyn FnOnce(&Gd<Node>) -> T;
 enum InitState<T> {
     ManualUninitialized,
     AutoPrepared { initializer: Box<InitFn<T>> },
-    AutoInitializing, // needed because state cannot be empty
+    AutoInitializationFailed,
     Initialized { value: T },
 }
 
@@ -324,7 +324,9 @@ impl<T: Debug> Debug for InitState<T> {
             InitState::AutoPrepared { .. } => {
                 fmt.debug_struct("AutoPrepared").finish_non_exhaustive()
             }
-            InitState::AutoInitializing => fmt.debug_struct("AutoInitializing").finish(),
+            InitState::AutoInitializationFailed => {
+                fmt.debug_struct("AutoInitializationFailed").finish()
+            }
             InitState::Initialized { value } => fmt
                 .debug_struct("Initialized")
                 .field("value", value)

itest/rust/src/object_tests/onready_test.rs

@@ -7,6 +7,8 @@
 
 // Integration of OnReady with #[init(load = "PATH")] is tested in save_load_test.rs.
 
+use std::ops::{Deref, DerefMut};
+
 use godot::classes::notify::NodeNotification;
 use godot::classes::{INode, Node};
 use godot::obj::{Gd, NewAlloc, OnReady};
@@ -33,6 +35,39 @@ fn onready_deref() {
     node.free();
 }
 
+#[itest]
+fn onready_poisoned() {
+    let node = Node::new_alloc();
+    let mut l = OnReady::<i32>::new(|| panic!("Auto init failure."));
+    expect_panic("Auto init must fail", || {
+        godot::private::auto_init(&mut l, &node)
+    });
+    expect_panic("Calling `init` after failed auto init fails", || {
+        l.init(44);
+    });
+
+    expect_panic(
+        "Calling `auto_init` again after failed auto init fails",
+        || {
+            godot::private::auto_init(&mut l, &node);
+        },
+    );
+    expect_panic(
+        "Panic on deref after automatic initialization failure",
+        || {
+            let _failed_deref = Deref::deref(&l);
+        },
+    );
+    expect_panic(
+        "Panic on deref mut after automatic initialization failure",
+        || {
+            let _failed_deref = DerefMut::deref_mut(&mut l);
+        },
+    );
+
+    node.free();
+}
+
 #[itest]
 fn onready_deref_on_uninit() {
     expect_panic("Deref on uninit fails", || {