Systematically optimize agentic editing performance (#28961)

Now that we've established a proper eval in tree, this PR is reboots of
our agent loop back to a set of minimal tools and simpler prompts. We
should aim to get this branch feeling subjectively competitive with
what's on main and then merge it, and build from there.

Let's invest in our eval and use it to drive better performance of the
agent loop. How you can help: Pick an example, and then make the outcome
faster or better. It's fine to even use your own subjective judgment, as
our evaluation criteria likely need tuning as well at this point. Focus
on making the agent work better in your own subjective experience first.
Let's focus on simple/practical improvements to make this thing work
better, then determine how we can craft our judgment criteria to lock
those improvements in.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Agus <agus@zed.dev>
Co-authored-by: Richard <richard@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/assistant_tools/src/edit_file_tool.rs

@@ -0,0 +1,183 @@
+use crate::{replace::replace_with_flexible_indent, schema::json_schema_for};
+use anyhow::{Context as _, Result, anyhow};
+use assistant_tool::{ActionLog, Tool, ToolResult};
+use gpui::{App, AppContext, AsyncApp, Entity, Task};
+use language_model::{LanguageModelRequestMessage, LanguageModelToolSchemaFormat};
+use project::Project;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use std::{path::PathBuf, sync::Arc};
+use ui::IconName;
+
+use crate::replace::replace_exact;
+
+#[derive(Debug, Serialize, Deserialize, JsonSchema)]
+pub struct EditFileToolInput {
+    /// The full path of the file to modify in the project.
+    ///
+    /// WARNING: When specifying which file path need changing, you MUST
+    /// start each path with one of the project's root directories.
+    ///
+    /// The following examples assume we have two root directories in the project:
+    /// - backend
+    /// - frontend
+    ///
+    /// <example>
+    /// `backend/src/main.rs`
+    ///
+    /// Notice how the file path starts with root-1. Without that, the path
+    /// would be ambiguous and the call would fail!
+    /// </example>
+    ///
+    /// <example>
+    /// `frontend/db.js`
+    /// </example>
+    pub path: PathBuf,
+
+    /// A user-friendly markdown description of what's being replaced. This will be shown in the UI.
+    ///
+    /// <example>Fix API endpoint URLs</example>
+    /// <example>Update copyright year in `page_footer`</example>
+    pub display_description: String,
+
+    /// The text to replace.
+    pub old_string: String,
+
+    /// The text to replace it with.
+    pub new_string: String,
+}
+
+pub struct EditFileTool;
+
+impl Tool for EditFileTool {
+    fn name(&self) -> String {
+        "edit_file".into()
+    }
+
+    fn needs_confirmation(&self, _: &serde_json::Value, _: &App) -> bool {
+        false
+    }
+
+    fn description(&self) -> String {
+        include_str!("edit_file_tool/description.md").to_string()
+    }
+
+    fn icon(&self) -> IconName {
+        IconName::Pencil
+    }
+
+    fn input_schema(&self, format: LanguageModelToolSchemaFormat) -> Result<serde_json::Value> {
+        json_schema_for::<EditFileToolInput>(format)
+    }
+
+    fn ui_text(&self, input: &serde_json::Value) -> String {
+        match serde_json::from_value::<EditFileToolInput>(input.clone()) {
+            Ok(input) => input.display_description,
+            Err(_) => "Edit file".to_string(),
+        }
+    }
+
+    fn run(
+        self: Arc<Self>,
+        input: serde_json::Value,
+        _messages: &[LanguageModelRequestMessage],
+        project: Entity<Project>,
+        action_log: Entity<ActionLog>,
+        cx: &mut App,
+    ) -> ToolResult {
+        let input = match serde_json::from_value::<EditFileToolInput>(input) {
+            Ok(input) => input,
+            Err(err) => return Task::ready(Err(anyhow!(err))).into(),
+        };
+
+        cx.spawn(async move |cx: &mut AsyncApp| {
+            let project_path = project.read_with(cx, |project, cx| {
+                project
+                    .find_project_path(&input.path, cx)
+                    .context("Path not found in project")
+            })??;
+
+            let buffer = project
+                .update(cx, |project, cx| project.open_buffer(project_path, cx))?
+                .await?;
+
+            let snapshot = buffer.read_with(cx, |buffer, _cx| buffer.snapshot())?;
+
+            if input.old_string.is_empty() {
+                return Err(anyhow!("`old_string` cannot be empty. Use a different tool if you want to create a file."));
+            }
+
+            if input.old_string == input.new_string {
+                return Err(anyhow!("The `old_string` and `new_string` are identical, so no changes would be made."));
+            }
+
+            let result = cx
+                .background_spawn(async move {
+                    // Try to match exactly
+                    let diff = replace_exact(&input.old_string, &input.new_string, &snapshot)
+                    .await
+                    // If that fails, try being flexible about indentation
+                    .or_else(|| replace_with_flexible_indent(&input.old_string, &input.new_string, &snapshot))?;
+
+                    if diff.edits.is_empty() {
+                        return None;
+                    }
+
+                    let old_text = snapshot.text();
+
+                    Some((old_text, diff))
+                })
+                .await;
+
+            let Some((old_text, diff)) = result else {
+                let err = buffer.read_with(cx, |buffer, _cx| {
+                    let file_exists = buffer
+                        .file()
+                        .map_or(false, |file| file.disk_state().exists());
+
+                    if !file_exists {
+                        anyhow!("{} does not exist", input.path.display())
+                    } else if buffer.is_empty() {
+                        anyhow!(
+                            "{} is empty, so the provided `old_string` wasn't found.",
+                            input.path.display()
+                        )
+                    } else {
+                        anyhow!("Failed to match the provided `old_string`")
+                    }
+                })?;
+
+                return Err(err)
+            };
+
+            let snapshot = cx.update(|cx| {
+                action_log.update(cx, |log, cx| {
+                    log.buffer_read(buffer.clone(), cx)
+                });
+                let snapshot = buffer.update(cx, |buffer, cx| {
+                    buffer.finalize_last_transaction();
+                    buffer.apply_diff(diff, cx);
+                    buffer.finalize_last_transaction();
+                    buffer.snapshot()
+                });
+                action_log.update(cx, |log, cx| {
+                    log.buffer_edited(buffer.clone(), cx)
+                });
+                snapshot
+            })?;
+
+            project.update( cx, |project, cx| {
+                project.save_buffer(buffer, cx)
+            })?.await?;
+
+            let diff_str = cx.background_spawn(async move {
+                let new_text = snapshot.text();
+                language::unified_diff(&old_text, &new_text)
+            }).await;
+
+
+            Ok(format!("Edited {}:\n\n```diff\n{}\n```", input.path.display(), diff_str))
+
+        }).into()
+    }
+}