agent: Support adding selection as context (#28964)

https://github.com/user-attachments/assets/42ebe911-3392-48f7-8583-caab285aca09

Release Notes:

- agent: Support adding selections via @selection or `assistant: Quote
selection` as context

crates/agent/src/context.rs

@@ -4,6 +4,7 @@ use gpui::{App, Entity, SharedString};
 use language::{Buffer, File};
 use language_model::LanguageModelRequestMessage;
 use project::{ProjectPath, Worktree};
+use rope::Point;
 use serde::{Deserialize, Serialize};
 use text::{Anchor, BufferId};
 use ui::IconName;
@@ -23,6 +24,7 @@ pub enum ContextKind {
     File,
     Directory,
     Symbol,
+    Excerpt,
     FetchedUrl,
     Thread,
 }
@@ -33,6 +35,7 @@ impl ContextKind {
             ContextKind::File => IconName::File,
             ContextKind::Directory => IconName::Folder,
             ContextKind::Symbol => IconName::Code,
+            ContextKind::Excerpt => IconName::Code,
             ContextKind::FetchedUrl => IconName::Globe,
             ContextKind::Thread => IconName::MessageBubbles,
         }
@@ -46,6 +49,7 @@ pub enum AssistantContext {
     Symbol(SymbolContext),
     FetchedUrl(FetchedUrlContext),
     Thread(ThreadContext),
+    Excerpt(ExcerptContext),
 }
 
 impl AssistantContext {
@@ -56,6 +60,7 @@ impl AssistantContext {
             Self::Symbol(symbol) => symbol.id,
             Self::FetchedUrl(url) => url.id,
             Self::Thread(thread) => thread.id,
+            Self::Excerpt(excerpt) => excerpt.id,
         }
     }
 }
@@ -155,6 +160,14 @@ pub struct ContextSymbolId {
     pub range: Range<Anchor>,
 }
 
+#[derive(Debug, Clone)]
+pub struct ExcerptContext {
+    pub id: ContextId,
+    pub range: Range<Anchor>,
+    pub line_range: Range<Point>,
+    pub context_buffer: ContextBuffer,
+}
+
 /// Formats a collection of contexts into a string representation
 pub fn format_context_as_string<'a>(
     contexts: impl Iterator<Item = &'a AssistantContext>,
@@ -163,6 +176,7 @@ pub fn format_context_as_string<'a>(
     let mut file_context = Vec::new();
     let mut directory_context = Vec::new();
     let mut symbol_context = Vec::new();
+    let mut excerpt_context = Vec::new();
     let mut fetch_context = Vec::new();
     let mut thread_context = Vec::new();
 
@@ -171,6 +185,7 @@ pub fn format_context_as_string<'a>(
             AssistantContext::File(context) => file_context.push(context),
             AssistantContext::Directory(context) => directory_context.push(context),
             AssistantContext::Symbol(context) => symbol_context.push(context),
+            AssistantContext::Excerpt(context) => excerpt_context.push(context),
             AssistantContext::FetchedUrl(context) => fetch_context.push(context),
             AssistantContext::Thread(context) => thread_context.push(context),
         }
@@ -179,6 +194,7 @@ pub fn format_context_as_string<'a>(
     if file_context.is_empty()
         && directory_context.is_empty()
         && symbol_context.is_empty()
+        && excerpt_context.is_empty()
         && fetch_context.is_empty()
         && thread_context.is_empty()
     {
@@ -216,6 +232,15 @@ pub fn format_context_as_string<'a>(
         result.push_str("</symbols>\n");
     }
 
+    if !excerpt_context.is_empty() {
+        result.push_str("<excerpts>\n");
+        for context in excerpt_context {
+            result.push_str(&context.context_buffer.text);
+            result.push('\n');
+        }
+        result.push_str("</excerpts>\n");
+    }
+
     if !fetch_context.is_empty() {
         result.push_str("<fetched_urls>\n");
         for context in &fetch_context {