Introduce a new /delta command (#17903)

Release Notes:

- Added a new `/delta` command to re-insert changed files that were
previously included in a context.

---------

Co-authored-by: Roy <roy@anthropic.com>

crates/assistant_slash_command/Cargo.toml

@@ -19,4 +19,5 @@ gpui.workspace = true
 language.workspace = true
 parking_lot.workspace = true
 serde.workspace = true
+serde_json.workspace = true
 workspace.workspace = true

crates/assistant_slash_command/src/assistant_slash_command.rs

@@ -2,7 +2,7 @@ mod slash_command_registry;
 
 use anyhow::Result;
 use gpui::{AnyElement, AppContext, ElementId, SharedString, Task, WeakView, WindowContext};
-use language::{CodeLabel, LspAdapterDelegate};
+use language::{BufferSnapshot, CodeLabel, LspAdapterDelegate, OffsetRangeExt};
 use serde::{Deserialize, Serialize};
 pub use slash_command_registry::*;
 use std::{
@@ -77,6 +77,8 @@ pub trait SlashCommand: 'static + Send + Sync {
     fn run(
         self: Arc<Self>,
         arguments: &[String],
+        context_slash_command_output_sections: &[SlashCommandOutputSection<language::Anchor>],
+        context_buffer: BufferSnapshot,
         workspace: WeakView<Workspace>,
         // TODO: We're just using the `LspAdapterDelegate` here because that is
         // what the extension API is already expecting.
@@ -94,7 +96,7 @@ pub type RenderFoldPlaceholder = Arc<
         + Fn(ElementId, Arc<dyn Fn(&mut WindowContext)>, &mut WindowContext) -> AnyElement,
 >;
 
-#[derive(Debug, Default)]
+#[derive(Debug, Default, PartialEq)]
 pub struct SlashCommandOutput {
     pub text: String,
     pub sections: Vec<SlashCommandOutputSection<usize>>,
@@ -106,4 +108,11 @@ pub struct SlashCommandOutputSection<T> {
     pub range: Range<T>,
     pub icon: IconName,
     pub label: SharedString,
+    pub metadata: Option<serde_json::Value>,
+}
+
+impl SlashCommandOutputSection<language::Anchor> {
+    pub fn is_valid(&self, buffer: &language::TextBuffer) -> bool {
+        self.range.start.is_valid(buffer) && !self.range.to_offset(buffer).is_empty()
+    }
 }