Add Response::parent_id and improve warn_if_rect_changes_id (#8010)

Reduces the amount of false positives

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui/src/containers/area.rs

@@ -516,6 +516,7 @@ impl Area {
             let move_response = ctx.create_widget(
                 WidgetRect {
                     id: interact_id,
+                    parent_id: id,
                     layer_id,
                     rect: state.rect(),
                     interact_rect: state.rect().intersect(constrain_rect),

crates/egui/src/containers/window.rs

@@ -962,6 +962,7 @@ fn do_resize_interaction(
             WidgetRect {
                 layer_id,
                 id,
+                parent_id: layer_id.id,
                 rect,
                 interact_rect: rect,
                 sense: Sense::DRAG, // Don't use Sense::drag() since we don't want these to be focusable

crates/egui/src/context.rs

@@ -1360,6 +1360,7 @@ impl Context {
 
         let WidgetRect {
             id,
+            parent_id: _,
             layer_id,
             rect,
             interact_rect,
@@ -4324,6 +4325,15 @@ fn warn_if_rect_changes_id(
                 continue;
             }
 
+            // Only warn if at least one widget has the same parent_id in both frames.
+            // If all parent_ids changed too, this is a cascading id shift, not a widget bug.
+            if !prev_at_rect
+                .iter()
+                .any(|pw| new_at_rect.iter().any(|nw| nw.parent_id == pw.parent_id))
+            {
+                continue;
+            }
+
             let rect = new_at_rect[0].rect;
 
             log::warn!(

crates/egui/src/hit_test.rs

@@ -450,6 +450,7 @@ mod tests {
     fn wr(id: Id, sense: Sense, rect: Rect) -> WidgetRect {
         WidgetRect {
             id,
+            parent_id: Id::NULL,
             layer_id: LayerId::background(),
             rect,
             interact_rect: rect,

crates/egui/src/response.rs

@@ -151,6 +151,22 @@ bitflags::bitflags! {
 }
 
 impl Response {
+    /// The [`Id`] of the parent [`crate::Ui`] that hosts this widget.
+    ///
+    /// Looks up the [`WidgetRect`] from the current (or previous) pass.
+    pub fn parent_id(&self) -> Id {
+        let id = self.ctx.viewport(|viewport| {
+            viewport
+                .this_pass
+                .widgets
+                .get(self.id)
+                .or_else(|| viewport.prev_pass.widgets.get(self.id))
+                .map(|w| w.parent_id)
+        });
+        debug_assert!(id.is_some(), "WidgetRect for Response not found!");
+        id.unwrap_or(Id::NULL)
+    }
+
     /// Returns true if this widget was clicked this frame by the primary button.
     ///
     /// A click is registered when the mouse or touch is released within
@@ -761,6 +777,7 @@ impl Response {
             WidgetRect {
                 layer_id: self.layer_id,
                 id: self.id,
+                parent_id: self.parent_id(),
                 rect: self.rect,
                 interact_rect: self.interact_rect,
                 sense: self.sense | sense,

crates/egui/src/style.rs

@@ -1303,7 +1303,8 @@ pub struct DebugOptions {
     /// Show interesting widgets under the mouse cursor.
     pub show_widget_hits: bool,
 
-    /// Show a warning if the same `Rect` had different `Id` on the previous frame.
+    /// Show a warning if the same `Rect` had different `Id` and the same parent `Id` on the
+    /// previous frame.
     pub warn_if_rect_changes_id: bool,
 
     /// If true, highlight widgets that are not aligned to [`emath::GUI_ROUNDING`].

crates/egui/src/ui.rs

@@ -173,6 +173,7 @@ impl Ui {
         ui.ctx().create_widget(
             WidgetRect {
                 id: ui.unique_id,
+                parent_id: ui.id,
                 layer_id: ui.layer_id(),
                 rect: start_rect,
                 interact_rect: start_rect,
@@ -339,6 +340,7 @@ impl Ui {
         child_ui.ctx().create_widget(
             WidgetRect {
                 id: child_ui.unique_id,
+                parent_id: self.id,
                 layer_id: child_ui.layer_id(),
                 rect: start_rect,
                 interact_rect: start_rect,
@@ -1043,6 +1045,7 @@ impl Ui {
         self.ctx().create_widget(
             WidgetRect {
                 id,
+                parent_id: self.id,
                 layer_id: self.layer_id(),
                 rect,
                 interact_rect: self.clip_rect().intersect(rect),
@@ -1112,6 +1115,7 @@ impl Ui {
         let mut response = self.ctx().create_widget(
             WidgetRect {
                 id: self.unique_id,
+                parent_id: self.id,
                 layer_id: self.layer_id(),
                 rect: self.min_rect(),
                 interact_rect: self.clip_rect().intersect(self.min_rect()),

crates/egui/src/widget_rect.rs

@@ -17,6 +17,12 @@ pub struct WidgetRect {
     /// You can ensure globally unique ids using [`crate::Ui::push_id`].
     pub id: Id,
 
+    /// The [`Id`] of the parent [`crate::Ui`] that hosts this widget.
+    ///
+    /// Used by debug checks to distinguish true id-instability from
+    /// cascading id shifts caused by a parent Ui's auto-id changing.
+    pub parent_id: Id,
+
     /// What layer the widget is on.
     pub layer_id: LayerId,
 
@@ -46,6 +52,7 @@ impl WidgetRect {
     pub fn transform(self, transform: emath::TSTransform) -> Self {
         let Self {
             id,
+            parent_id,
             layer_id,
             rect,
             interact_rect,
@@ -54,6 +61,7 @@ impl WidgetRect {
         } = self;
         Self {
             id,
+            parent_id,
             layer_id,
             rect: transform * rect,
             interact_rect: transform * interact_rect,

tests/egui_tests/tests/regression_tests.rs

@@ -280,6 +280,49 @@ fn warn_if_rect_changes_id() {
     );
 }
 
+/// When a parent Ui's id changes (e.g. via `push_id` with a dynamic value),
+/// all child widget ids shift too. This should NOT trigger `warn_if_rect_changes_id` because the
+/// `parent_id` also changed — it's a cascading id shift, not a widget bug.
+#[test]
+fn warn_if_rect_changes_id_false_positive_parent_shift() {
+    use std::cell::Cell;
+
+    let counter = Cell::new(0);
+    let button_rect = egui::Rect::from_min_size(egui::pos2(10.0, 10.0), egui::vec2(100.0, 30.0));
+
+    let mut harness = Harness::builder().with_size((200.0, 100.0)).build_ui(|ui| {
+        // push_id with a changing value causes the child Ui's id to shift,
+        // which in turn shifts all widget ids inside it.
+        ui.push_id(counter.get(), |ui| {
+            let id = ui.id().with("my_widget");
+            let _response = ui.interact(button_rect, id, Sense::click());
+        });
+    });
+
+    // Frame 1: counter=0 — establishes prev_pass
+    harness.step();
+    assert!(
+        !has_red_warning_rect(harness.output()),
+        "Should not warn on first frame"
+    );
+
+    // Frame 2: counter=0 — prev_pass == this_pass
+    harness.step();
+    assert!(
+        !has_red_warning_rect(harness.output()),
+        "Should not warn when nothing changed"
+    );
+
+    // Now change the parent id, shifting all child widget ids
+    counter.set(1);
+    harness.step();
+
+    assert!(
+        !has_red_warning_rect(harness.output()),
+        "Should NOT warn when parent Ui's id shifted (cascading id change)"
+    );
+}
+
 #[test]
 fn horizontal_wrapped_multiline_row_height() {
     let mut harness = Harness::builder().with_size((350.0, 300.0)).build_ui(|ui| {