Improve styling of tabs

* Enforce a min width per tab
* Center the title within tab, regardless of icon
* Render icon over the top of the tab title
* Ensure there is always a fixed minimum amount of filler to the right of all tabs

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

gpui/src/elements/align.rs

@@ -3,7 +3,7 @@ use crate::{
     LayoutContext, PaintContext, SizeConstraint,
 };
 use json::ToJson;
-use pathfinder_geometry::vector::{vec2f, Vector2F};
+use pathfinder_geometry::vector::Vector2F;
 use serde_json::json;
 
 pub struct Align {
@@ -19,8 +19,13 @@ impl Align {
         }
     }
 
-    pub fn top_center(mut self) -> Self {
-        self.alignment = vec2f(0.0, -1.0);
+    pub fn top(mut self) -> Self {
+        self.alignment.set_y(-1.0);
+        self
+    }
+
+    pub fn right(mut self) -> Self {
+        self.alignment.set_x(1.0);
         self
     }
 }

gpui/src/elements/constrained_box.rs

@@ -23,6 +23,11 @@ impl ConstrainedBox {
         }
     }
 
+    pub fn with_min_width(mut self, min_width: f32) -> Self {
+        self.constraint.min.set_x(min_width);
+        self
+    }
+
     pub fn with_max_width(mut self, max_width: f32) -> Self {
         self.constraint.max.set_x(max_width);
         self
@@ -33,6 +38,12 @@ impl ConstrainedBox {
         self
     }
 
+    pub fn with_width(mut self, width: f32) -> Self {
+        self.constraint.min.set_x(width);
+        self.constraint.max.set_x(width);
+        self
+    }
+
     pub fn with_height(mut self, height: f32) -> Self {
         self.constraint.min.set_y(height);
         self.constraint.max.set_y(height);
@@ -51,6 +62,7 @@ impl Element for ConstrainedBox {
     ) -> (Vector2F, Self::LayoutState) {
         constraint.min = constraint.min.max(self.constraint.min);
         constraint.max = constraint.max.min(self.constraint.max);
+        constraint.max = constraint.max.max(constraint.min);
         let size = self.child.layout(constraint, ctx);
         (size, ())
     }

gpui/src/elements/container.rs

@@ -43,6 +43,18 @@ impl Container {
         self
     }
 
+    pub fn with_horizontal_padding(mut self, padding: f32) -> Self {
+        self.padding.left = padding;
+        self.padding.right = padding;
+        self
+    }
+
+    pub fn with_vertical_padding(mut self, padding: f32) -> Self {
+        self.padding.top = padding;
+        self.padding.bottom = padding;
+        self
+    }
+
     pub fn with_uniform_padding(mut self, padding: f32) -> Self {
         self.padding = Padding {
             top: padding,

gpui/src/elements/flex.rs

@@ -1,4 +1,4 @@
-use std::any::Any;
+use std::{any::Any, f32::INFINITY};
 
 use crate::{
     json::{self, ToJson, Value},
@@ -88,9 +88,13 @@ impl Element for Flex {
             let mut remaining_space = constraint.max_along(self.axis) - fixed_space;
             let mut remaining_flex = total_flex;
             for child in &mut self.children {
-                let space_per_flex = remaining_space / remaining_flex;
                 if let Some(flex) = Self::child_flex(&child) {
-                    let child_max = space_per_flex * flex;
+                    let child_max = if remaining_flex == 0.0 {
+                        remaining_space
+                    } else {
+                        let space_per_flex = remaining_space / remaining_flex;
+                        space_per_flex * flex
+                    };
                     let child_constraint = match self.axis {
                         Axis::Horizontal => SizeConstraint::new(
                             vec2f(0.0, constraint.min.y()),