assistant edit tool: Replace with flexible indentation (#27039)

Sometimes the model produces SEARCH queries that don't match the
indentation of the source file exactly.

When we can't find an exact match, we'll now attempt to match the lines
while being more flexible about the leading whitespace as long as all
lines are consistently offset from the source, and extend the leading
whitespace in the REPLACE string accordingly.

Release Notes:

- N/A

crates/assistant_tools/src/edit_files_tool.rs

@@ -1,5 +1,6 @@
 mod edit_action;
 pub mod log;
+mod replace;
 
 use anyhow::{anyhow, Context, Result};
 use assistant_tool::{ActionLog, Tool};
@@ -11,12 +12,12 @@ use language_model::{
     LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, MessageContent, Role,
 };
 use log::{EditToolLog, EditToolRequestId};
-use project::{search::SearchQuery, Project};
+use project::Project;
+use replace::{replace_exact, replace_with_flexible_indent};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::fmt::Write;
 use std::sync::Arc;
-use util::paths::PathMatcher;
 use util::ResultExt;
 
 #[derive(Debug, Serialize, Deserialize, JsonSchema)]
@@ -289,41 +290,18 @@ impl EditToolRequest {
         file_path: std::path::PathBuf,
         snapshot: language::BufferSnapshot,
     ) -> Result<DiffResult> {
-        let query = SearchQuery::text(
-            old.clone(),
-            false,
-            true,
-            true,
-            PathMatcher::new(&[])?,
-            PathMatcher::new(&[])?,
-            None,
-        )?;
+        let result =
+            // Try to match exactly
+            replace_exact(&old, &new, &snapshot)
+            .await
+            // If that fails, try being flexible about indentation
+            .or_else(|| replace_with_flexible_indent(&old, &new, &snapshot));
 
-        let matches = query.search(&snapshot, None).await;
-
-        if matches.is_empty() {
-            return Ok(DiffResult::BadSearch(BadSearch {
-                search: old.clone(),
+        let Some(diff) = result else {
+            return anyhow::Ok(DiffResult::BadSearch(BadSearch {
+                search: old,
                 file_path: file_path.display().to_string(),
             }));
-        }
-
-        let edit_range = matches[0].clone();
-        let diff = language::text_diff(&old, &new);
-
-        let edits = diff
-            .into_iter()
-            .map(|(old_range, text)| {
-                let start = edit_range.start + old_range.start;
-                let end = edit_range.start + old_range.end;
-                (start..end, text)
-            })
-            .collect::<Vec<_>>();
-
-        let diff = language::Diff {
-            base_version: snapshot.version().clone(),
-            line_ending: snapshot.line_ending(),
-            edits,
         };
 
         anyhow::Ok(DiffResult::Diff(diff))