Combine excerpt footer and header into a single block (#19441)

This simplifies rendering of excerpt headers and footers, and removes
the need to store a `BlockDisposition` on these boundary blocks. It's a
step toward implementing "replace blocks", which we want to use in the
assistant panel.

We've also cleaned up the way heights are specified for headers and
footers and fixed some visual asymmetries between the "expand upward"
and "expand downward" buttons.

Release Notes:

- N/A

---------

Co-authored-by: Richard <richard@zed.dev>

crates/editor/src/editor.rs

@@ -73,12 +73,12 @@ use git::blame::GitBlame;
 use gpui::{
     div, impl_actions, point, prelude::*, px, relative, size, uniform_list, Action, AnyElement,
     AppContext, AsyncWindowContext, AvailableSpace, BackgroundExecutor, Bounds, ClipboardEntry,
-    ClipboardItem, Context, DispatchPhase, ElementId, EntityId, EventEmitter, FocusHandle,
-    FocusOutEvent, FocusableView, FontId, FontWeight, HighlightStyle, Hsla, InteractiveText,
-    KeyContext, ListSizingBehavior, Model, MouseButton, PaintQuad, ParentElement, Pixels, Render,
-    SharedString, Size, StrikethroughStyle, Styled, StyledText, Subscription, Task, TextStyle,
-    UTF16Selection, UnderlineStyle, UniformListScrollHandle, View, ViewContext, ViewInputHandler,
-    VisualContext, WeakFocusHandle, WeakView, WindowContext,
+    ClipboardItem, Context, DispatchPhase, ElementId, EventEmitter, FocusHandle, FocusOutEvent,
+    FocusableView, FontId, FontWeight, HighlightStyle, Hsla, InteractiveText, KeyContext,
+    ListSizingBehavior, Model, MouseButton, PaintQuad, ParentElement, Pixels, Render, SharedString,
+    Size, StrikethroughStyle, Styled, StyledText, Subscription, Task, TextStyle, UTF16Selection,
+    UnderlineStyle, UniformListScrollHandle, View, ViewContext, ViewInputHandler, VisualContext,
+    WeakFocusHandle, WeakView, WindowContext,
 };
 use highlight_matching_bracket::refresh_matching_bracket_highlights;
 use hover_popover::{hide_hover, HoverState};
@@ -171,7 +171,7 @@ use workspace::{Item as WorkspaceItem, OpenInTerminal, OpenTerminal, TabBarSetti
 use crate::hover_links::find_url;
 use crate::signature_help::{SignatureHelpHiddenBy, SignatureHelpState};
 
-pub const FILE_HEADER_HEIGHT: u32 = 1;
+pub const FILE_HEADER_HEIGHT: u32 = 2;
 pub const MULTI_BUFFER_EXCERPT_HEADER_HEIGHT: u32 = 1;
 pub const MULTI_BUFFER_EXCERPT_FOOTER_HEIGHT: u32 = 1;
 pub const DEFAULT_MULTIBUFFER_CONTEXT: u32 = 2;
@@ -640,7 +640,6 @@ pub struct Editor {
     tasks: BTreeMap<(BufferId, BufferRow), RunnableTasks>,
     tasks_update_task: Option<Task<()>>,
     previous_search_ranges: Option<Arc<[Range<Anchor>]>>,
-    file_header_size: u32,
     breadcrumb_header: Option<String>,
     focused_block: Option<FocusedBlock>,
     next_scroll_position: NextScrollCursorCenterTopBottom,
@@ -1846,7 +1845,6 @@ impl Editor {
             }),
             merge_adjacent: true,
         };
-        let file_header_size = if show_excerpt_controls { 3 } else { 2 };
         let display_map = cx.new_model(|cx| {
             DisplayMap::new(
                 buffer.clone(),
@@ -1854,7 +1852,7 @@ impl Editor {
                 font_size,
                 None,
                 show_excerpt_controls,
-                file_header_size,
+                FILE_HEADER_HEIGHT,
                 MULTI_BUFFER_EXCERPT_HEADER_HEIGHT,
                 MULTI_BUFFER_EXCERPT_FOOTER_HEIGHT,
                 fold_placeholder,
@@ -2038,7 +2036,6 @@ impl Editor {
                 .restore_unsaved_buffers,
             blame: None,
             blame_subscription: None,
-            file_header_size,
             tasks: Default::default(),
             _subscriptions: vec![
                 cx.observe(&buffer, Self::on_buffer_changed),
@@ -12808,7 +12805,7 @@ impl Editor {
     }
 
     pub fn file_header_size(&self) -> u32 {
-        self.file_header_size
+        FILE_HEADER_HEIGHT
     }
 
     pub fn revert(
@@ -14120,7 +14117,7 @@ pub fn diagnostic_block_renderer(
 
         let multi_line_diagnostic = diagnostic.message.contains('\n');
 
-        let buttons = |diagnostic: &Diagnostic, block_id: BlockId| {
+        let buttons = |diagnostic: &Diagnostic| {
             if multi_line_diagnostic {
                 v_flex()
             } else {
@@ -14128,7 +14125,7 @@ pub fn diagnostic_block_renderer(
             }
             .when(allow_closing, |div| {
                 div.children(diagnostic.is_primary.then(|| {
-                    IconButton::new(("close-block", EntityId::from(block_id)), IconName::XCircle)
+                    IconButton::new("close-block", IconName::XCircle)
                         .icon_color(Color::Muted)
                         .size(ButtonSize::Compact)
                         .style(ButtonStyle::Transparent)
@@ -14138,7 +14135,7 @@ pub fn diagnostic_block_renderer(
                 }))
             })
             .child(
-                IconButton::new(("copy-block", EntityId::from(block_id)), IconName::Copy)
+                IconButton::new("copy-block", IconName::Copy)
                     .icon_color(Color::Muted)
                     .size(ButtonSize::Compact)
                     .style(ButtonStyle::Transparent)
@@ -14153,7 +14150,7 @@ pub fn diagnostic_block_renderer(
             )
         };
 
-        let icon_size = buttons(&diagnostic, cx.block_id)
+        let icon_size = buttons(&diagnostic)
             .into_any_element()
             .layout_as_root(AvailableSpace::min_size(), cx);
 
@@ -14170,7 +14167,7 @@ pub fn diagnostic_block_renderer(
                     .w(cx.anchor_x - cx.gutter_dimensions.width - icon_size.width)
                     .flex_shrink(),
             )
-            .child(buttons(&diagnostic, cx.block_id))
+            .child(buttons(&diagnostic))
             .child(div().flex().flex_shrink_0().child(
                 StyledText::new(text_without_backticks.clone()).with_highlights(
                     &text_style,