Polish diff for the edit_file tool (#29911)

I added some padding to the editor, and removed the border around each
hunk as it would overlap in weird ways with the card container.

## Before

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/2018feaa-c847-4609-bc82-522660714b9a"
/>

## After

One Light:

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/4da1a4b6-0af2-4479-afcc-02da50178fd6"
/>

One Dark:

<img width="1148" alt="image"
src="https://github.com/user-attachments/assets/0168631d-7b76-4582-8174-c6e9c1297dc8"
/>


Release Notes:

- Improved displaying of diffs when the agent edits files.

crates/assistant_tools/Cargo.toml

@@ -50,13 +50,13 @@ strsim.workspace = true
 task.workspace = true
 terminal.workspace = true
 terminal_view.workspace = true
+theme.workspace = true
 ui.workspace = true
 util.workspace = true
 web_search.workspace = true
 workspace-hack.workspace = true
 workspace.workspace = true
 zed_llm_client.workspace = true
-theme.workspace = true
 
 [dev-dependencies]
 client = { workspace = true, features = ["test-support"] }

crates/assistant_tools/src/edit_file_tool.rs

@@ -5,10 +5,10 @@ use crate::{
 use anyhow::{Context as _, Result, anyhow};
 use assistant_tool::{ActionLog, AnyToolCard, Tool, ToolCard, ToolResult, ToolUseStatus};
 use buffer_diff::{BufferDiff, BufferDiffSnapshot};
-use editor::{Editor, EditorMode, MultiBuffer, PathKey};
+use editor::{Editor, EditorElement, EditorMode, EditorStyle, MultiBuffer, PathKey};
 use gpui::{
     Animation, AnimationExt, AnyWindowHandle, App, AppContext, AsyncApp, Context, Entity, EntityId,
-    Task, TextStyleRefinement, WeakEntity, pulsating_between,
+    Task, TextStyle, TextStyleRefinement, WeakEntity, pulsating_between,
 };
 use language::{
     Anchor, Buffer, Capability, LanguageRegistry, LineEnding, OffsetRangeExt, Rope, TextBuffer,
@@ -382,14 +382,13 @@ impl EditFileToolCard {
                         .map(|diff_hunk| diff_hunk.buffer_range.to_point(&snapshot))
                         .collect::<Vec<_>>();
                     multibuffer.clear(cx);
-                    let (_, is_newly_added) = multibuffer.set_excerpts_for_path(
+                    multibuffer.set_excerpts_for_path(
                         PathKey::for_buffer(&buffer, cx),
                         buffer,
                         diff_hunk_ranges,
                         editor::DEFAULT_MULTIBUFFER_CONTEXT,
                         cx,
                     );
-                    debug_assert!(is_newly_added);
                     multibuffer.add_diff(buffer_diff, cx);
                     let end = multibuffer.len(cx);
                     Some(multibuffer.snapshot(cx).offset_to_point(end).row + 1)
@@ -554,7 +553,30 @@ impl ToolCard for EditFileToolCard {
                 .map(|style| style.text.line_height_in_pixels(window.rem_size()))
                 .unwrap_or_default();
 
-            let element = editor.render(window, cx);
+            let settings = ThemeSettings::get_global(cx);
+            let element = EditorElement::new(
+                &cx.entity(),
+                EditorStyle {
+                    background: cx.theme().colors().editor_background,
+                    horizontal_padding: rems(0.25).to_pixels(window.rem_size()),
+                    local_player: cx.theme().players().local(),
+                    text: TextStyle {
+                        color: cx.theme().colors().editor_foreground,
+                        font_family: settings.buffer_font.family.clone(),
+                        font_features: settings.buffer_font.features.clone(),
+                        font_fallbacks: settings.buffer_font.fallbacks.clone(),
+                        font_size: settings.buffer_font_size(cx).into(),
+                        font_weight: settings.buffer_font.weight,
+                        line_height: relative(settings.buffer_line_height.value()),
+                        ..Default::default()
+                    },
+                    scrollbar_width: EditorElement::SCROLLBAR_WIDTH,
+                    syntax: cx.theme().syntax().clone(),
+                    status: cx.theme().status().clone(),
+                    ..Default::default()
+                },
+            );
+
             (element.into_any_element(), line_height)
         });
 
@@ -775,9 +797,16 @@ async fn build_buffer_diff(
         })?
         .await;
 
+    let secondary_diff = cx.new(|cx| {
+        let mut diff = BufferDiff::new(&buffer, cx);
+        diff.set_snapshot(diff_snapshot.clone(), &buffer, cx);
+        diff
+    })?;
+
     cx.new(|cx| {
         let mut diff = BufferDiff::new(&buffer.text, cx);
-        diff.set_snapshot(diff_snapshot, &buffer.text, cx);
+        diff.set_snapshot(diff_snapshot, &buffer, cx);
+        diff.set_secondary_diff(secondary_diff);
         diff
     })
 }

crates/editor/src/editor.rs

@@ -517,6 +517,7 @@ pub enum SoftWrap {
 #[derive(Clone)]
 pub struct EditorStyle {
     pub background: Hsla,
+    pub horizontal_padding: Pixels,
     pub local_player: PlayerColor,
     pub text: TextStyle,
     pub scrollbar_width: Pixels,
@@ -531,6 +532,7 @@ impl Default for EditorStyle {
     fn default() -> Self {
         Self {
             background: Hsla::default(),
+            horizontal_padding: Pixels::default(),
             local_player: PlayerColor::default(),
             text: TextStyle::default(),
             scrollbar_width: Pixels::default(),
@@ -20352,6 +20354,7 @@ impl Render for Editor {
             &cx.entity(),
             EditorStyle {
                 background,
+                horizontal_padding: Pixels::default(),
                 local_player: cx.theme().players().local(),
                 text: text_style,
                 scrollbar_width: EditorElement::SCROLLBAR_WIDTH,

crates/editor/src/element.rs

@@ -170,7 +170,7 @@ pub struct EditorElement {
 type DisplayRowDelta = u32;
 
 impl EditorElement {
-    pub(crate) const SCROLLBAR_WIDTH: Pixels = px(15.);
+    pub const SCROLLBAR_WIDTH: Pixels = px(15.);
 
     pub fn new(editor: &Entity<Editor>, style: EditorStyle) -> Self {
         Self {
@@ -6810,10 +6810,27 @@ impl Element for EditorElement {
                             cx,
                         )
                         .unwrap_or_default();
-                    let text_width = bounds.size.width - gutter_dimensions.width;
+                    let hitbox = window.insert_hitbox(bounds, false);
+                    let gutter_hitbox =
+                        window.insert_hitbox(gutter_bounds(bounds, gutter_dimensions), false);
+                    let text_hitbox = window.insert_hitbox(
+                        Bounds {
+                            origin: gutter_hitbox.top_right()
+                                + point(style.horizontal_padding, Pixels::default()),
+                            size: size(
+                                bounds.size.width
+                                    - gutter_dimensions.width
+                                    - 2. * style.horizontal_padding,
+                                bounds.size.height,
+                            ),
+                        },
+                        false,
+                    );
 
-                    let editor_width =
-                        text_width - gutter_dimensions.margin - em_width - style.scrollbar_width;
+                    let editor_width = text_hitbox.size.width
+                        - gutter_dimensions.margin
+                        - em_width
+                        - style.scrollbar_width;
 
                     snapshot = self.editor.update(cx, |editor, cx| {
                         editor.last_bounds = Some(bounds);
@@ -6849,24 +6866,13 @@ impl Element for EditorElement {
                         .map(|(guide, active)| (self.column_pixels(*guide, window, cx), *active))
                         .collect::<SmallVec<[_; 2]>>();
 
-                    let hitbox = window.insert_hitbox(bounds, false);
-                    let gutter_hitbox =
-                        window.insert_hitbox(gutter_bounds(bounds, gutter_dimensions), false);
-                    let text_hitbox = window.insert_hitbox(
-                        Bounds {
-                            origin: gutter_hitbox.top_right(),
-                            size: size(text_width, bounds.size.height),
-                        },
-                        false,
-                    );
-
                     // Offset the content_bounds from the text_bounds by the gutter margin (which
                     // is roughly half a character wide) to make hit testing work more like how we want.
                     let content_offset = point(gutter_dimensions.margin, Pixels::ZERO);
                     let content_origin = text_hitbox.origin + content_offset;
 
                     let editor_text_bounds =
-                        Bounds::from_corners(content_origin, bounds.bottom_right());
+                        Bounds::from_corners(content_origin, text_hitbox.bounds.bottom_right());
 
                     let height_in_lines = editor_text_bounds.size.height / line_height;