From 823905cd3b70ad95556f37d5ebed279cb1aef558 Mon Sep 17 00:00:00 2001
From: Tobias Hunger <tobias.hunger@slint.dev>
Date: Wed, 26 Mar 2025 11:20:41 +0000
Subject: [PATCH] interpreter: Support debug-hooks

---
 internal/interpreter/api.rs               |  8 +++++
 internal/interpreter/debug_hook.rs        | 37 +++++++++++++++++++++++
 internal/interpreter/dynamic_item_tree.rs |  2 +-
 internal/interpreter/eval.rs              |  8 ++++-
 internal/interpreter/global_component.rs  | 10 +++++-
 internal/interpreter/lib.rs               |  2 ++
 6 files changed, 64 insertions(+), 3 deletions(-)
 create mode 100644 internal/interpreter/debug_hook.rs

diff --git a/internal/interpreter/api.rs b/internal/interpreter/api.rs
index 148be397eb0..9579c0ff385 100644
--- a/internal/interpreter/api.rs
+++ b/internal/interpreter/api.rs
@@ -1527,6 +1527,14 @@ impl ComponentInstance {
     ) -> Vec<(i_slint_compiler::object_tree::ElementRc, usize)> {
         crate::highlight::element_node_at_source_code_position(&self.inner, path, offset)
     }
+
+    /// Set a callback triggered by `Expression::DebugHook``.
+    #[cfg(feature = "internal-highlight")]
+    pub fn set_debug_hook_callback(&self, callback: Option<crate::debug_hook::DebugHookCallback>) {
+        generativity::make_guard!(guard);
+        let comp = self.inner.unerase(guard);
+        crate::debug_hook::set_debug_hook_callback(comp, callback);
+    }
 }
 
 impl ComponentHandle for ComponentInstance {
diff --git a/internal/interpreter/debug_hook.rs b/internal/interpreter/debug_hook.rs
new file mode 100644
index 00000000000..0ba10e6ae1e
--- /dev/null
+++ b/internal/interpreter/debug_hook.rs
@@ -0,0 +1,37 @@
+// Copyright © SixtyFPS GmbH <info@slint.dev>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
+
+use crate::{dynamic_item_tree, Value};
+
+use smol_str::SmolStr;
+
+use std::pin::Pin;
+
+pub type DebugHookCallback = Box<dyn Fn(&str, crate::Value) -> Value>;
+
+pub(crate) fn set_debug_hook_callback(
+    component: Pin<&dynamic_item_tree::ItemTreeBox>,
+    func: Option<DebugHookCallback>,
+) {
+    let Some(global_storage) = component.description().compiled_globals.clone() else {
+        return;
+    };
+    *(global_storage.debug_hook_callback.borrow_mut()) = func;
+}
+
+pub(crate) fn debug_hook_triggered(
+    component_instance: &dynamic_item_tree::InstanceRef,
+    id: SmolStr,
+    value: Value,
+) -> Value {
+    let Some(global_storage) = component_instance.description.compiled_globals.clone() else {
+        return value;
+    };
+    let callback = global_storage.debug_hook_callback.borrow();
+
+    if let Some(callback) = callback.as_ref() {
+        callback(id.as_str(), value)
+    } else {
+        value
+    }
+}
diff --git a/internal/interpreter/dynamic_item_tree.rs b/internal/interpreter/dynamic_item_tree.rs
index 9d06b14878f..6cce8065ed3 100644
--- a/internal/interpreter/dynamic_item_tree.rs
+++ b/internal/interpreter/dynamic_item_tree.rs
@@ -402,7 +402,7 @@ pub struct ItemTreeDescription<'id> {
     pub(crate) popup_menu_description: PopupMenuDescription,
 
     /// The collection of compiled globals
-    compiled_globals: Option<Rc<CompiledGlobalCollection>>,
+    pub(crate) compiled_globals: Option<Rc<CompiledGlobalCollection>>,
 
     /// The type loader, which will be available only on the top-most `ItemTreeDescription`.
     /// All other `ItemTreeDescription`s have `None` here.
diff --git a/internal/interpreter/eval.rs b/internal/interpreter/eval.rs
index e18a8d32fbb..d166bf15c35 100644
--- a/internal/interpreter/eval.rs
+++ b/internal/interpreter/eval.rs
@@ -396,7 +396,13 @@ pub fn eval_expression(expression: &Expression, local_context: &mut EvalLocalCon
             }
         }
         Expression::EmptyComponentFactory => Value::ComponentFactory(Default::default()),
-        Expression::DebugHook { expression, .. } => eval_expression(expression, local_context),
+        Expression::DebugHook { expression, id: _id } => {
+            let value = eval_expression(expression, local_context);
+            #[cfg(feature = "internal-highlight")]
+            let value = crate::debug_hook::debug_hook_triggered(&local_context.component_instance, _id.clone(), value);
+            value
+
+        }
     }
 }
 
diff --git a/internal/interpreter/global_component.rs b/internal/interpreter/global_component.rs
index 96958137ad2..5c17f1caa90 100644
--- a/internal/interpreter/global_component.rs
+++ b/internal/interpreter/global_component.rs
@@ -23,6 +23,9 @@ pub struct CompiledGlobalCollection {
     /// Map of all exported global singletons and their index in the compiled_globals vector. The key
     /// is the normalized name of the global.
     pub exported_globals_by_name: BTreeMap<SmolStr, usize>,
+
+    #[cfg(feature = "internal-highlight")]
+    pub(crate) debug_hook_callback: RefCell<Option<crate::debug_hook::DebugHookCallback>>,
 }
 
 impl CompiledGlobalCollection {
@@ -54,7 +57,12 @@ impl CompiledGlobalCollection {
                 global
             })
             .collect();
-        Self { compiled_globals, exported_globals_by_name }
+        Self {
+            compiled_globals,
+            exported_globals_by_name,
+            #[cfg(feature = "internal-highlight")]
+            debug_hook_callback: RefCell::new(None),
+        }
     }
 }
 
diff --git a/internal/interpreter/lib.rs b/internal/interpreter/lib.rs
index f8efd56c89b..c7f11b54732 100644
--- a/internal/interpreter/lib.rs
+++ b/internal/interpreter/lib.rs
@@ -79,6 +79,8 @@ compile_error!(
 );
 
 mod api;
+#[cfg(feature = "internal-highlight")]
+mod debug_hook;
 mod dynamic_item_tree;
 mod dynamic_type;
 mod eval;