Pass PaintContext to Element::paint

I want to use this on another branch, but it's a sweeping change,
so this prepares the ground for it. This can always be reverted if
it doesn't work out.

crates/gpui/src/app.rs

@@ -44,6 +44,7 @@ use window_input_handler::WindowInputHandler;
 use crate::{
     elements::{AnyElement, AnyRootElement, RootElement},
     executor::{self, Task},
+    fonts::TextStyle,
     json,
     keymap_matcher::{self, Binding, KeymapContext, KeymapMatcher, Keystroke, MatchResult},
     platform::{
@@ -3363,6 +3364,7 @@ pub struct LayoutContext<'a, 'b, 'c, V: View> {
     view_context: &'c mut ViewContext<'a, 'b, V>,
     new_parents: &'c mut HashMap<usize, usize>,
     views_to_notify_if_ancestors_change: &'c mut HashMap<usize, SmallVec<[usize; 2]>>,
+    text_style_stack: Vec<Arc<TextStyle>>,
     pub refreshing: bool,
 }
 
@@ -3377,6 +3379,7 @@ impl<'a, 'b, 'c, V: View> LayoutContext<'a, 'b, 'c, V> {
             view_context,
             new_parents,
             views_to_notify_if_ancestors_change,
+            text_style_stack: Vec::new(),
             refreshing,
         }
     }
@@ -3428,6 +3431,24 @@ impl<'a, 'b, 'c, V: View> LayoutContext<'a, 'b, 'c, V> {
             .or_default()
             .push(self_view_id);
     }
+
+    pub fn text_style(&self) -> Arc<TextStyle> {
+        self.text_style_stack
+            .last()
+            .cloned()
+            .unwrap_or(Default::default())
+    }
+
+    pub fn with_text_style<S, F, T>(&mut self, style: S, f: F) -> T
+    where
+        S: Into<Arc<TextStyle>>,
+        F: FnOnce(&mut Self) -> T,
+    {
+        self.text_style_stack.push(style.into());
+        let result = f(self);
+        self.text_style_stack.pop();
+        result
+    }
 }
 
 impl<'a, 'b, 'c, V: View> Deref for LayoutContext<'a, 'b, 'c, V> {
@@ -3464,6 +3485,72 @@ impl<V: View> BorrowWindowContext for LayoutContext<'_, '_, '_, V> {
     }
 }
 
+pub struct PaintContext<'a, 'b, 'c, V: View> {
+    view_context: &'c mut ViewContext<'a, 'b, V>,
+    text_style_stack: Vec<Arc<TextStyle>>,
+}
+
+impl<'a, 'b, 'c, V: View> PaintContext<'a, 'b, 'c, V> {
+    pub fn new(view_context: &'c mut ViewContext<'a, 'b, V>) -> Self {
+        Self {
+            view_context,
+            text_style_stack: Vec::new(),
+        }
+    }
+
+    pub fn text_style(&self) -> Arc<TextStyle> {
+        self.text_style_stack
+            .last()
+            .cloned()
+            .unwrap_or(Default::default())
+    }
+
+    pub fn with_text_style<S, F, T>(&mut self, style: S, f: F) -> T
+    where
+        S: Into<Arc<TextStyle>>,
+        F: FnOnce(&mut Self) -> T,
+    {
+        self.text_style_stack.push(style.into());
+        let result = f(self);
+        self.text_style_stack.pop();
+        result
+    }
+}
+
+impl<'a, 'b, 'c, V: View> Deref for PaintContext<'a, 'b, 'c, V> {
+    type Target = ViewContext<'a, 'b, V>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.view_context
+    }
+}
+
+impl<V: View> DerefMut for PaintContext<'_, '_, '_, V> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.view_context
+    }
+}
+
+impl<V: View> BorrowAppContext for PaintContext<'_, '_, '_, V> {
+    fn read_with<T, F: FnOnce(&AppContext) -> T>(&self, f: F) -> T {
+        BorrowAppContext::read_with(&*self.view_context, f)
+    }
+
+    fn update<T, F: FnOnce(&mut AppContext) -> T>(&mut self, f: F) -> T {
+        BorrowAppContext::update(&mut *self.view_context, f)
+    }
+}
+
+impl<V: View> BorrowWindowContext for PaintContext<'_, '_, '_, V> {
+    fn read_with<T, F: FnOnce(&WindowContext) -> T>(&self, window_id: usize, f: F) -> T {
+        BorrowWindowContext::read_with(&*self.view_context, window_id, f)
+    }
+
+    fn update<T, F: FnOnce(&mut WindowContext) -> T>(&mut self, window_id: usize, f: F) -> T {
+        BorrowWindowContext::update(&mut *self.view_context, window_id, f)
+    }
+}
+
 pub struct EventContext<'a, 'b, 'c, V: View> {
     view_context: &'c mut ViewContext<'a, 'b, V>,
     pub(crate) handled: bool,