Add the ability to follow the agent as it makes edits (#29839)

Nathan here: I also tacked on a bunch of UI refinement.

Release Notes:

- Introduced the ability to follow the agent around as it reads and
edits files.

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/assistant_tools/src/read_file_tool.rs

@@ -6,8 +6,9 @@ use gpui::{AnyWindowHandle, App, Entity, Task};
 
 use indoc::formatdoc;
 use itertools::Itertools;
+use language::{Anchor, Point};
 use language_model::{LanguageModelRequestMessage, LanguageModelToolSchemaFormat};
-use project::Project;
+use project::{AgentLocation, Project};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
@@ -35,11 +36,11 @@ pub struct ReadFileToolInput {
 
     /// Optional line number to start reading on (1-based index)
     #[serde(default)]
-    pub start_line: Option<usize>,
+    pub start_line: Option<u32>,
 
     /// Optional line number to end reading on (1-based index, inclusive)
     #[serde(default)]
-    pub end_line: Option<usize>,
+    pub end_line: Option<u32>,
 }
 
 pub struct ReadFileTool;
@@ -109,7 +110,7 @@ impl Tool for ReadFileTool {
         let file_path = input.path.clone();
         cx.spawn(async move |cx| {
             if !exists.await? {
-                return Err(anyhow!("{} not found", file_path))
+                return Err(anyhow!("{} not found", file_path));
             }
 
             let buffer = cx
@@ -118,25 +119,54 @@ impl Tool for ReadFileTool {
                 })?
                 .await?;
 
+            project.update(cx, |project, cx| {
+                project.set_agent_location(
+                    Some(AgentLocation {
+                        buffer: buffer.downgrade(),
+                        position: Anchor::MIN,
+                    }),
+                    cx,
+                );
+            })?;
+
             // Check if specific line ranges are provided
             if input.start_line.is_some() || input.end_line.is_some() {
+                let mut anchor = None;
                 let result = buffer.read_with(cx, |buffer, _cx| {
                     let text = buffer.text();
                     // .max(1) because despite instructions to be 1-indexed, sometimes the model passes 0.
                     let start = input.start_line.unwrap_or(1).max(1);
-                    let lines = text.split('\n').skip(start - 1);
+                    let start_row = start - 1;
+                    if start_row <= buffer.max_point().row {
+                        let column = buffer.line_indent_for_row(start_row).raw_len();
+                        anchor = Some(buffer.anchor_before(Point::new(start_row, column)));
+                    }
+
+                    let lines = text.split('\n').skip(start_row as usize);
                     if let Some(end) = input.end_line {
                         let count = end.saturating_sub(start).saturating_add(1); // Ensure at least 1 line
-                        Itertools::intersperse(lines.take(count), "\n").collect()
+                        Itertools::intersperse(lines.take(count as usize), "\n").collect()
                     } else {
                         Itertools::intersperse(lines, "\n").collect()
                     }
                 })?;
 
                 action_log.update(cx, |log, cx| {
-                    log.track_buffer(buffer, cx);
+                    log.track_buffer(buffer.clone(), cx);
                 })?;
 
+                if let Some(anchor) = anchor {
+                    project.update(cx, |project, cx| {
+                        project.set_agent_location(
+                            Some(AgentLocation {
+                                buffer: buffer.downgrade(),
+                                position: anchor,
+                            }),
+                            cx,
+                        );
+                    })?;
+                }
+
                 Ok(result)
             } else {
                 // No line ranges specified, so check file size to see if it's too big.
@@ -165,7 +195,8 @@ impl Tool for ReadFileTool {
                     })
                 }
             }
-        }).into()
+        })
+        .into()
     }
 }