Put `Theme` behind an `Arc` (#3017)

Marshall Bowers and Piotr Osiewicz created 2 years ago

This PR puts the `Theme` returned from the `theme` function behind an
`Arc`.

### Motivation

While working on wiring up window focus events for the `TitleBar`
component we ran into issues where `theme` was holding an immutable
borrow to the `ViewContext` for the entirety of the `render` scope,
which prevented having mutable borrows in the same scope.

### Explanation

To avoid this, we can make `theme` return an `Arc<Theme>` to allow for
cheap clones and avoiding the issues with the borrow checker.

Release Notes:

- N/A

Co-authored-by: Piotr Osiewicz <[e-mail]>

Change summary

crates/gpui/src/app/window.rs           | 14 +++++++++-----
crates/storybook/src/collab_panel.rs    | 14 +++++++-------
crates/ui/src/templates/collab_panel.rs | 14 +++++++-------
crates/ui/src/templates/status_bar.rs   |  4 ++--
crates/ui/src/theme.rs                  |  3 ++-
5 files changed, 27 insertions(+), 22 deletions(-)

Detailed changes

crates/gpui/src/app/window.rs

@@ -33,6 +33,7 @@ use std::{
     any::{type_name, Any, TypeId},
     mem,
     ops::{Deref, DerefMut, Range, Sub},
+    sync::Arc,
 };
 use taffy::{
     tree::{Measurable, MeasureFunc},
@@ -56,7 +57,7 @@ pub struct Window {
     pub(crate) rendered_views: HashMap<usize, Box<dyn AnyRootElement>>,
     scene: SceneBuilder,
     pub(crate) text_style_stack: Vec<TextStyle>,
-    pub(crate) theme_stack: Vec<Box<dyn Any>>,
+    pub(crate) theme_stack: Vec<Arc<dyn Any + Send + Sync>>,
     pub(crate) new_parents: HashMap<usize, usize>,
     pub(crate) views_to_notify_if_ancestors_change: HashMap<usize, SmallVec<[usize; 2]>>,
     titlebar_height: f32,
@@ -1336,18 +1337,21 @@ impl<'a> WindowContext<'a> {
         self.window.text_style_stack.pop();
     }
 
-    pub fn theme<T: 'static>(&self) -> &T {
+    pub fn theme<T: 'static + Send + Sync>(&self) -> Arc<T> {
         self.window
             .theme_stack
             .iter()
             .rev()
-            .find_map(|theme| theme.downcast_ref())
+            .find_map(|theme| {
+                let entry = Arc::clone(theme);
+                entry.downcast::<T>().ok()
+            })
             .ok_or_else(|| anyhow!("no theme provided of type {}", type_name::<T>()))
             .unwrap()
     }
 
-    pub fn push_theme<T: 'static>(&mut self, theme: T) {
-        self.window.theme_stack.push(Box::new(theme));
+    pub fn push_theme<T: 'static + Send + Sync>(&mut self, theme: T) {
+        self.window.theme_stack.push(Arc::new(theme));
     }
 
     pub fn pop_theme(&mut self) {

crates/storybook/src/collab_panel.rs

@@ -52,12 +52,12 @@ impl<V: 'static> CollabPanelElement<V> {
                             //:: https://tailwindcss.com/docs/hover-focus-and-other-states#styling-based-on-parent-state
                             // .group()
                             // List Section Header
-                            .child(self.list_section_header("#CRDB", true, theme))
+                            .child(self.list_section_header("#CRDB", true, &theme))
                             // List Item Large
                             .child(self.list_item(
                                 "http://github.com/maxbrunsfeld.png?s=50",
                                 "maxbrunsfeld",
-                                theme,
+                                &theme,
                             )),
                     )
                     .child(
@@ -65,31 +65,31 @@ impl<V: 'static> CollabPanelElement<V> {
                             .py_2()
                             .flex()
                             .flex_col()
-                            .child(self.list_section_header("CHANNELS", true, theme)),
+                            .child(self.list_section_header("CHANNELS", true, &theme)),
                     )
                     .child(
                         div()
                             .py_2()
                             .flex()
                             .flex_col()
-                            .child(self.list_section_header("CONTACTS", true, theme))
+                            .child(self.list_section_header("CONTACTS", true, &theme))
                             .children(
                                 std::iter::repeat_with(|| {
                                     vec![
                                         self.list_item(
                                             "http://github.com/as-cii.png?s=50",
                                             "as-cii",
-                                            theme,
+                                            &theme,
                                         ),
                                         self.list_item(
                                             "http://github.com/nathansobo.png?s=50",
                                             "nathansobo",
-                                            theme,
+                                            &theme,
                                         ),
                                         self.list_item(
                                             "http://github.com/maxbrunsfeld.png?s=50",
                                             "maxbrunsfeld",
-                                            theme,
+                                            &theme,
                                         ),
                                     ]
                                 })

crates/ui/src/templates/collab_panel.rs

@@ -52,12 +52,12 @@ impl<V: 'static> CollabPanelElement<V> {
                             //:: https://tailwindcss.com/docs/hover-focus-and-other-states#styling-based-on-parent-state
                             // .group()
                             // List Section Header
-                            .child(self.list_section_header("#CRDB", true, theme))
+                            .child(self.list_section_header("#CRDB", true, &theme))
                             // List Item Large
                             .child(self.list_item(
                                 "http://github.com/maxbrunsfeld.png?s=50",
                                 "maxbrunsfeld",
-                                theme,
+                                &theme,
                             )),
                     )
                     .child(
@@ -65,31 +65,31 @@ impl<V: 'static> CollabPanelElement<V> {
                             .py_2()
                             .flex()
                             .flex_col()
-                            .child(self.list_section_header("CHANNELS", true, theme)),
+                            .child(self.list_section_header("CHANNELS", true, &theme)),
                     )
                     .child(
                         div()
                             .py_2()
                             .flex()
                             .flex_col()
-                            .child(self.list_section_header("CONTACTS", true, theme))
+                            .child(self.list_section_header("CONTACTS", true, &theme))
                             .children(
                                 std::iter::repeat_with(|| {
                                     vec![
                                         self.list_item(
                                             "http://github.com/as-cii.png?s=50",
                                             "as-cii",
-                                            theme,
+                                            &theme,
                                         ),
                                         self.list_item(
                                             "http://github.com/nathansobo.png?s=50",
                                             "nathansobo",
-                                            theme,
+                                            &theme,
                                         ),
                                         self.list_item(
                                             "http://github.com/maxbrunsfeld.png?s=50",
                                             "maxbrunsfeld",
-                                            theme,
+                                            &theme,
                                         ),
                                     ]
                                 })

crates/ui/src/templates/status_bar.rs

@@ -96,8 +96,8 @@ impl<V: 'static> StatusBar<V> {
             .justify_between()
             .w_full()
             .fill(theme.lowest.base.default.background)
-            .child(self.left_tools(theme))
-            .child(self.right_tools(theme))
+            .child(self.left_tools(&theme))
+            .child(self.right_tools(&theme))
     }
 
     fn left_tools(&self, theme: &Theme) -> impl Element<V> {

crates/ui/src/theme.rs

@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::fmt;
 use std::marker::PhantomData;
+use std::sync::Arc;
 
 use gpui2::color::Hsla;
 use gpui2::element::Element;
@@ -190,6 +191,6 @@ fn preferred_theme<V: 'static>(cx: &AppContext) -> Theme {
         .clone()
 }
 
-pub fn theme<'a>(cx: &'a WindowContext) -> &'a Theme {
+pub fn theme(cx: &WindowContext) -> Arc<Theme> {
     cx.theme::<Theme>()
 }