From dbd277e899990271da6c7ea6af4a705b5ee678de Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Fri, 14 Jun 2024 17:39:05 +0100
Subject: [PATCH 1/6] recompose

---
 src/textual/_compose.py | 28 ++++++++++++++++++++++++++++
 src/textual/app.py      | 10 +++++++---
 src/textual/dom.py      | 13 +++++++++++++
 src/textual/widget.py   | 10 ++++++++--
 4 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/src/textual/_compose.py b/src/textual/_compose.py
index 482b27fb6a..1d18b9e67d 100644
--- a/src/textual/_compose.py
+++ b/src/textual/_compose.py
@@ -76,3 +76,31 @@ def compose(node: App | Widget) -> list[Widget]:
         app._compose_stacks.pop()
         app._composed.pop()
     return nodes
+
+
+def recompose(node: App | Widget) -> tuple[list[Widget], set[Widget]]:
+    """Recompose a node (nodes with a matching nodes will have their state copied).
+
+    Args:
+        Node to be recomposed.
+
+    Returns:
+        A list of new nodes, and a list of nodes to be removed.
+    """
+    children: list[Widget] = list(
+        child for child in node.children if not child.has_class("-textual-system")
+    )
+    children_by_id = {child.id: child for child in children if child.id is not None}
+    new_children: list[Widget] = []
+    remove_children: set[Widget] = set(children)
+    for node in compose(node):
+        if node.id is None:
+            new_children.append(node)
+        else:
+            if (existing_child := children_by_id.pop(node.id, None)) is not None:
+                new_children.append(existing_child)
+                remove_children.discard(existing_child)
+                existing_child.copy_state(node)
+            else:
+                new_children.append(node)
+    return (new_children, remove_children)
diff --git a/src/textual/app.py b/src/textual/app.py
index a9237dc6ec..fa4118194d 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -70,6 +70,7 @@
 from ._ansi_theme import ALABASTER, MONOKAI
 from ._callback import invoke
 from ._compose import compose
+from ._compose import recompose as recompose_node
 from ._compositor import CompositorUpdate
 from ._context import active_app, active_message_pump
 from ._context import message_hook as message_hook_context_var
@@ -2620,9 +2621,12 @@ async def recompose(self) -> None:
         if self._exit:
             return
         try:
-            async with self.screen.batch():
-                await self.screen.query("*").exclude(".-textual-system").remove()
-                await self.screen.mount_all(compose(self))
+            new_children, remove_children = recompose_node(self.screen)
+            print("new", new_children)
+            print("remove", remove_children)
+            await self.app._remove_nodes(list(remove_children), self.screen)
+            if self.screen.is_attached:
+                await self.screen.mount_all(new_children)
         except ScreenStackError:
             pass
 
diff --git a/src/textual/dom.py b/src/textual/dom.py
index c8243d1edd..c3f7e4c3f7 100644
--- a/src/textual/dom.py
+++ b/src/textual/dom.py
@@ -284,6 +284,19 @@ def compose(self) -> ComposeResult:
             self.call_later(self._initialize_data_bind)
         return self
 
+    def copy_state(self, node: DOMNode) -> None:
+        """Copy the state from another node.
+
+        The default implementation will copy over reactives with the same name,
+        but this method may be override for different strategies.
+
+        Args:
+            node: A node to copy state from.
+        """
+        for key in node._reactives:
+            if key in self._reactives:
+                setattr(self, key, getattr(node, key))
+
     def _initialize_data_bind(self) -> None:
         """initialize a data binding.
 
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 5c701695c3..8c2c0c1f5d 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -48,6 +48,7 @@
 from ._animator import DEFAULT_EASING, Animatable, BoundAnimator, EasingFunction
 from ._arrange import DockArrangeResult, arrange
 from ._compose import compose
+from ._compose import recompose as recompose_node
 from ._context import NoActiveAppError, active_app
 from ._easing import DEFAULT_SCROLL_EASING
 from ._layout import Layout
@@ -1130,9 +1131,14 @@ async def recompose(self) -> None:
         if not self.is_attached:
             return
         async with self.batch():
-            await self.query("*").exclude(".-textual-system").remove()
+            new_children, remove_children = recompose_node(self)
+            await self.app._remove_nodes(list(remove_children), self)
             if self.is_attached:
-                await self.mount_all(compose(self))
+                await self.mount_all(new_children)
+
+            # await self.query("*").exclude(".-textual-system").remove()
+            # if self.is_attached:
+            #     await self.mount_all(compose(self))
 
     def _post_register(self, app: App) -> None:
         """Called when the instance is registered.

From 38ace6f62e3319e3c1a6a8954dd2eee3a6e2f9b3 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Fri, 14 Jun 2024 17:57:07 +0100
Subject: [PATCH 2/6] debug

---
 src/textual/_compose.py | 23 +++++++++++++----------
 src/textual/app.py      |  3 +++
 src/textual/widget.py   |  2 ++
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/textual/_compose.py b/src/textual/_compose.py
index 1d18b9e67d..96b23e4e58 100644
--- a/src/textual/_compose.py
+++ b/src/textual/_compose.py
@@ -88,19 +88,22 @@ def recompose(node: App | Widget) -> tuple[list[Widget], set[Widget]]:
         A list of new nodes, and a list of nodes to be removed.
     """
     children: list[Widget] = list(
-        child for child in node.children if not child.has_class("-textual-system")
+        child for child in node._nodes if not child.has_class("-textual-system")
     )
     children_by_id = {child.id: child for child in children if child.id is not None}
     new_children: list[Widget] = []
     remove_children: set[Widget] = set(children)
-    for node in compose(node):
-        if node.id is None:
-            new_children.append(node)
+    print("?", node)
+    for compose_node in compose(node):
+        print("!!", compose_node)
+        if (
+            compose_node.id is not None
+            and (existing_child := children_by_id.pop(compose_node.id, None))
+            is not None
+        ):
+            new_children.append(existing_child)
+            remove_children.discard(existing_child)
+            existing_child.copy_state(compose_node)
         else:
-            if (existing_child := children_by_id.pop(node.id, None)) is not None:
-                new_children.append(existing_child)
-                remove_children.discard(existing_child)
-                existing_child.copy_state(node)
-            else:
-                new_children.append(node)
+            new_children.append(compose_node)
     return (new_children, remove_children)
diff --git a/src/textual/app.py b/src/textual/app.py
index fa4118194d..c0863a729f 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -2618,8 +2618,11 @@ async def recompose(self) -> None:
 
         Recomposing will remove children and call `self.compose` again to remount.
         """
+
         if self._exit:
             return
+        await self.screen.recompose()
+        return
         try:
             new_children, remove_children = recompose_node(self.screen)
             print("new", new_children)
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 8c2c0c1f5d..1695273a9b 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -1132,6 +1132,8 @@ async def recompose(self) -> None:
             return
         async with self.batch():
             new_children, remove_children = recompose_node(self)
+            print("widget new", new_children)
+            print("widget remove", remove_children)
             await self.app._remove_nodes(list(remove_children), self)
             if self.is_attached:
                 await self.mount_all(new_children)

From e92507aba8988b1c434b2f73e16e5af1579b30e2 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Fri, 14 Jun 2024 18:21:16 +0100
Subject: [PATCH 3/6] app recompose

---
 src/textual/_compose.py | 11 ++++++-----
 src/textual/app.py      | 15 +++++++--------
 src/textual/widget.py   |  9 ++-------
 3 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/src/textual/_compose.py b/src/textual/_compose.py
index 96b23e4e58..e8d9869d0c 100644
--- a/src/textual/_compose.py
+++ b/src/textual/_compose.py
@@ -78,11 +78,14 @@ def compose(node: App | Widget) -> list[Widget]:
     return nodes
 
 
-def recompose(node: App | Widget) -> tuple[list[Widget], set[Widget]]:
+def recompose(
+    node: App | Widget, compose_node: App | Widget | None = None
+) -> tuple[list[Widget], set[Widget]]:
     """Recompose a node (nodes with a matching nodes will have their state copied).
 
     Args:
-        Node to be recomposed.
+        node: Node to be recomposed.
+        compose_node: Node where new nodes are composed, or `None` for the same node.
 
     Returns:
         A list of new nodes, and a list of nodes to be removed.
@@ -93,9 +96,7 @@ def recompose(node: App | Widget) -> tuple[list[Widget], set[Widget]]:
     children_by_id = {child.id: child for child in children if child.id is not None}
     new_children: list[Widget] = []
     remove_children: set[Widget] = set(children)
-    print("?", node)
-    for compose_node in compose(node):
-        print("!!", compose_node)
+    for compose_node in compose(node if compose_node is None else compose_node):
         if (
             compose_node.id is not None
             and (existing_child := children_by_id.pop(compose_node.id, None))
diff --git a/src/textual/app.py b/src/textual/app.py
index c0863a729f..be8ef47ec3 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -2621,15 +2621,14 @@ async def recompose(self) -> None:
 
         if self._exit:
             return
-        await self.screen.recompose()
-        return
+
         try:
-            new_children, remove_children = recompose_node(self.screen)
-            print("new", new_children)
-            print("remove", remove_children)
-            await self.app._remove_nodes(list(remove_children), self.screen)
-            if self.screen.is_attached:
-                await self.screen.mount_all(new_children)
+            screen = self.screen
+            new_children, remove_children = recompose_node(screen, self)
+            async with screen.batch():
+                await self.app._remove_nodes(list(remove_children), self.screen)
+                if self.screen.is_attached:
+                    await self.screen.mount_all(new_children)
         except ScreenStackError:
             pass
 
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 1695273a9b..210d06634a 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -1132,16 +1132,11 @@ async def recompose(self) -> None:
             return
         async with self.batch():
             new_children, remove_children = recompose_node(self)
-            print("widget new", new_children)
-            print("widget remove", remove_children)
-            await self.app._remove_nodes(list(remove_children), self)
+            if remove_children:
+                await self.app._remove_nodes(list(remove_children), self)
             if self.is_attached:
                 await self.mount_all(new_children)
 
-            # await self.query("*").exclude(".-textual-system").remove()
-            # if self.is_attached:
-            #     await self.mount_all(compose(self))
-
     def _post_register(self, app: App) -> None:
         """Called when the instance is registered.
 

From a6e70c67d8891cfe8d58e426eca741fc88db4cb5 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Fri, 14 Jun 2024 19:00:56 +0100
Subject: [PATCH 4/6] move to end

---
 CHANGELOG.md              |  7 +++++++
 src/textual/_node_list.py | 10 ++++++++++
 src/textual/app.py        |  4 +++-
 src/textual/dom.py        |  8 +++++---
 src/textual/reactive.py   |  9 +++++++++
 5 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7a4854f20f..6003180822 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Changed
+
+- Recompose will now keep widgets with matching IDs (with the same parent)
+- Added `state` to Reactive
+
 ## [0.68.0] - 2024-06-14
 
 ### Added
diff --git a/src/textual/_node_list.py b/src/textual/_node_list.py
index ac9b425f32..6aff990e3d 100644
--- a/src/textual/_node_list.py
+++ b/src/textual/_node_list.py
@@ -119,6 +119,16 @@ def _insert(self, index: int, widget: Widget) -> None:
                 self._nodes_by_id[widget_id] = widget
             self._updates += 1
 
+    def _move_to_end(self, widget: Widget) -> None:
+        """Move a widget to the end.
+
+        Args:
+            widget: Widget to move (should be in the list).
+        """
+        if widget in self._nodes_set:
+            self._nodes.remove(widget)
+            self._nodes.append(widget)
+
     def _ensure_unique_id(self, widget_id: str) -> None:
         if widget_id in self._nodes_by_id:
             raise DuplicateIds(
diff --git a/src/textual/app.py b/src/textual/app.py
index be8ef47ec3..7a09b6a44c 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -2718,7 +2718,9 @@ def _register(
         for widget in widget_list:
             if not isinstance(widget, Widget):
                 raise AppError(f"Can't register {widget!r}; expected a Widget instance")
-            if widget not in self._registry:
+            if widget in self._registry:
+                parent._nodes._move_to_end(widget)
+            else:
                 self._register_child(parent, widget, before, after)
                 if widget._nodes:
                     self._register(widget, *widget._nodes, cache=cache)
diff --git a/src/textual/dom.py b/src/textual/dom.py
index c3f7e4c3f7..61e2523ce9 100644
--- a/src/textual/dom.py
+++ b/src/textual/dom.py
@@ -293,9 +293,11 @@ def copy_state(self, node: DOMNode) -> None:
         Args:
             node: A node to copy state from.
         """
-        for key in node._reactives:
-            if key in self._reactives:
-                setattr(self, key, getattr(node, key))
+        for key, reactive in node._reactives.items():
+            if reactive.state:
+                if key in self._reactives:
+                    if hasattr(node, reactive.internal_name):
+                        setattr(self, key, getattr(node, key))
 
     def _initialize_data_bind(self) -> None:
         """initialize a data binding.
diff --git a/src/textual/reactive.py b/src/textual/reactive.py
index c9b153a743..d9de57a5c6 100644
--- a/src/textual/reactive.py
+++ b/src/textual/reactive.py
@@ -122,6 +122,7 @@ def __init__(
         compute: bool = True,
         recompose: bool = False,
         bindings: bool = False,
+        state: bool = True,
     ) -> None:
         self._default = default
         self._layout = layout
@@ -132,6 +133,7 @@ def __init__(
         self._recompose = recompose
         self._bindings = bindings
         self._owner: Type[MessageTarget] | None = None
+        self.state = state
 
     def __rich_repr__(self) -> rich.repr.Result:
         yield self._default
@@ -141,6 +143,7 @@ def __rich_repr__(self) -> rich.repr.Result:
         yield "always_update", self._always_update
         yield "compute", self._run_compute
         yield "recompose", self._recompose
+        yield "state", self.state
 
     @property
     def owner(self) -> Type[MessageTarget]:
@@ -375,6 +378,7 @@ class reactive(Reactive[ReactiveType]):
         init: Call watchers on initialize (post mount).
         always_update: Call watchers even when the new value equals the old value.
         bindings: Refresh bindings when the reactive changes.
+        state: Include this value in `copy_state`.
     """
 
     def __init__(
@@ -387,6 +391,7 @@ def __init__(
         always_update: bool = False,
         recompose: bool = False,
         bindings: bool = False,
+        state: bool = True,
     ) -> None:
         super().__init__(
             default,
@@ -396,6 +401,7 @@ def __init__(
             always_update=always_update,
             recompose=recompose,
             bindings=bindings,
+            state=state,
         )
 
 
@@ -407,6 +413,7 @@ class var(Reactive[ReactiveType]):
         init: Call watchers on initialize (post mount).
         always_update: Call watchers even when the new value equals the old value.
         bindings: Refresh bindings when the reactive changes.
+        state: Include this value in `copy_state`.
     """
 
     def __init__(
@@ -415,6 +422,7 @@ def __init__(
         init: bool = True,
         always_update: bool = False,
         bindings: bool = False,
+        state: bool = True,
     ) -> None:
         super().__init__(
             default,
@@ -423,6 +431,7 @@ def __init__(
             init=init,
             always_update=always_update,
             bindings=bindings,
+            state=state,
         )
 
 

From 24080530ec940bf7899d95293eb09d681f4ce994 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sun, 16 Jun 2024 07:48:26 +0100
Subject: [PATCH 5/6] tests

---
 tests/test_recompose.py | 46 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 tests/test_recompose.py

diff --git a/tests/test_recompose.py b/tests/test_recompose.py
new file mode 100644
index 0000000000..40ee406713
--- /dev/null
+++ b/tests/test_recompose.py
@@ -0,0 +1,46 @@
+from textual.app import App, ComposeResult
+from textual.containers import Vertical
+from textual.widgets import Input, Label
+
+
+async def test_recompose_preserve_id():
+    """Check recomposing leaves widgets with matching ID."""
+
+    class MyVertical(Vertical):
+        def compose(self) -> ComposeResult:
+            yield Label("foo", classes="foo", name="foo")
+            yield Input(id="bar", name="bar")
+            yield Label("baz", classes="baz", name="baz")
+
+    class RecomposeApp(App):
+        def compose(self) -> ComposeResult:
+            yield MyVertical()
+
+    app = RecomposeApp()
+    async with app.run_test() as pilot:
+        foo = app.query_one(".foo")
+        bar = app.query_one("#bar")
+        baz = app.query_one(".baz")
+        assert [node.name for node in app.query("MyVertical > *")] == [
+            "foo",
+            "bar",
+            "baz",
+        ]
+
+        bar.focus()
+        await pilot.press("h", "i")
+        await app.query_one(MyVertical).recompose()
+
+        # Order shouldn't change
+        assert [node.name for node in app.query("MyVertical > *")] == [
+            "foo",
+            "bar",
+            "baz",
+        ]
+
+        # Check that only the ID is the same instance
+        assert app.query_one(".foo") is not foo  # New instance
+        assert app.query_one("#bar") is bar  # Matching id, so old instance
+        assert app.query_one(".baz") is not baz  # new instance
+
+        assert app.query_one("#bar", Input).value == "hi"

From dd3ff8492e8b8264cd905fa2d36e9dfc5eb37195 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Mon, 17 Jun 2024 21:22:43 +0100
Subject: [PATCH 6/6] wip

---
 src/textual/_compose.py             | 43 +++++++++++++++++++++++++++++
 src/textual/_node_list.py           | 10 +++++++
 src/textual/widgets/_footer.py      |  6 +++-
 src/textual/widgets/_placeholder.py |  1 +
 4 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/src/textual/_compose.py b/src/textual/_compose.py
index e8d9869d0c..50e26b3bea 100644
--- a/src/textual/_compose.py
+++ b/src/textual/_compose.py
@@ -78,6 +78,26 @@ def compose(node: App | Widget) -> list[Widget]:
     return nodes
 
 
+def _pending_children(
+    node: Widget, children_by_id: dict[str, Widget]
+) -> dict[str, Widget]:
+    def recurse_children(widget: Widget):
+        children: list[Widget] = list(
+            child
+            for child in widget._pending_children
+            if not child.has_class("-textual-system")
+        )
+
+        if widget.id is not None and widget.id not in children_by_id:
+            children_by_id[widget.id] = widget
+        for child in children:
+            recurse_children(child)
+
+    recurse_children(node)
+
+    return children_by_id
+
+
 def recompose(
     node: App | Widget, compose_node: App | Widget | None = None
 ) -> tuple[list[Widget], set[Widget]]:
@@ -96,7 +116,25 @@ def recompose(
     children_by_id = {child.id: child for child in children if child.id is not None}
     new_children: list[Widget] = []
     remove_children: set[Widget] = set(children)
+
+    composed = compose(node if compose_node is None else compose_node)
+
     for compose_node in compose(node if compose_node is None else compose_node):
+        _pending_children(compose_node, children_by_id)
+
+    def recurse_pending(node: Widget) -> None:
+        print("recurse", node, children_by_id)
+        for child in list(node._nodes):
+            if child.id is not None and child.id in children_by_id:
+                print(1)
+                existing_child = children_by_id.pop(child.id)
+                if node._nodes._replace(child, existing_child):
+                    remove_children.add(child)
+            else:
+                print(2)
+                recurse_pending(child)
+
+    for compose_node in composed:
         if (
             compose_node.id is not None
             and (existing_child := children_by_id.pop(compose_node.id, None))
@@ -107,4 +145,9 @@ def recompose(
             existing_child.copy_state(compose_node)
         else:
             new_children.append(compose_node)
+            recurse_pending(node)
+
+    node.log(children_by_id)
+    print(new_children, remove_children)
+
     return (new_children, remove_children)
diff --git a/src/textual/_node_list.py b/src/textual/_node_list.py
index f448a6f493..7e8f75c3cd 100644
--- a/src/textual/_node_list.py
+++ b/src/textual/_node_list.py
@@ -128,6 +128,16 @@ def _move_to_end(self, widget: Widget) -> None:
         if widget in self._nodes_set:
             self._nodes.remove(widget)
             self._nodes.append(widget)
+            self._updates += 1
+
+    def _replace(self, widget: Widget, new_widget: Widget) -> bool:
+        try:
+            index = self._nodes.index(widget)
+        except ValueError:
+            return False
+        else:
+            self._nodes[index] = new_widget
+        return True
 
     def _ensure_unique_id(self, widget_id: str) -> None:
         if widget_id in self._nodes_by_id:
diff --git a/src/textual/widgets/_footer.py b/src/textual/widgets/_footer.py
index aa39e3719e..2632c84bc2 100644
--- a/src/textual/widgets/_footer.py
+++ b/src/textual/widgets/_footer.py
@@ -9,6 +9,7 @@
 from ..app import ComposeResult
 from ..binding import Binding
 from ..containers import ScrollableContainer
+from ..dom import NoScreen
 from ..reactive import reactive
 from ..widget import Widget
 
@@ -173,7 +174,10 @@ async def bindings_changed(screen: Screen) -> None:
         self.screen.bindings_updated_signal.subscribe(self, bindings_changed)
 
     def on_unmount(self) -> None:
-        self.screen.bindings_updated_signal.unsubscribe(self)
+        try:
+            self.screen.bindings_updated_signal.unsubscribe(self)
+        except NoScreen:
+            pass
 
     def watch_compact(self, compact: bool) -> None:
         self.set_class(compact, "-compact")
diff --git a/src/textual/widgets/_placeholder.py b/src/textual/widgets/_placeholder.py
index 3b210db921..0208d18994 100644
--- a/src/textual/widgets/_placeholder.py
+++ b/src/textual/widgets/_placeholder.py
@@ -143,6 +143,7 @@ def render(self) -> RenderResult:
         Returns:
             The value to render.
         """
+        return str(id(self))
         return self._renderables[self.variant]
 
     def cycle_variant(self) -> Self: