feat: Tampilkan unified diff pada hasil tool edit

src/tool/fs/edit.rs

@@ -9,7 +9,8 @@ use super::super::Tool;
 use super::super::ToolCtx;
 use super::super::resolve_path;
 use super::super::check_graduated_checks;
-use super::helpers::arg_str;
+use super::helpers::{self, arg_str};
+use similar::TextDiff;
 
 /// Tool: replace text in a file. Requires the old string to be unique unless `replace_all` is true.
 pub struct Edit;
@@ -99,11 +100,12 @@ impl Tool for Edit {
         };
         fs::write(&path, &new_content)
             .map_err(|e| anyhow!("failed to write '{rel}': {e}"))?;
-        let bytes_diff = if new_content.len() > content.len() {
-            new_content.len() - content.len()
-        } else {
-            content.len() - new_content.len()
-        };
+        let text_diff = TextDiff::from_lines(content.as_str(), new_content.as_str());
+        let diff_text = format!(
+            "{}",
+            text_diff.unified_diff().context_radius(3).header(&rel, &rel)
+        );
+        let diff_block = format!("```diff\n{}\n```", helpers::truncate_diff(&diff_text));
         // Notify the LSP server of the on-disk change so diagnostics stay fresh.
         // Never fail the edit because of this — LSP errors are surfaced as a
         // trailing annotation on the success message instead.
@@ -114,9 +116,60 @@ impl Tool for Edit {
             String::new()
         };
         if check_matches.is_empty() {
-            Ok(format!("edited {} ({} byte delta){}", rel, bytes_diff as isize, lsp_note))
+            Ok(format!("edited {rel}\n{diff_block}{lsp_note}"))
         } else {
-            Ok(format!("edited {} ({} byte delta). Graduated checks matched: {}{}", rel, bytes_diff as isize, check_matches.join(", "), lsp_note))
+            Ok(format!("edited {rel}. Graduated checks matched: {}\n{diff_block}{lsp_note}", check_matches.join(", ")))
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn test_ctx(workspace: std::path::PathBuf) -> crate::tool::ToolCtx {
+        crate::tool::ToolCtx::builder().workspaces(vec![workspace]).build()
+    }
+
+    fn temp_workspace() -> std::path::PathBuf {
+        let dir = std::env::temp_dir().join(format!("zesdex-edit-test-{}", uuid::Uuid::new_v4()));
+        fs::create_dir_all(&dir).unwrap();
+        dir
+    }
+
+    #[test]
+    fn edit_returns_a_diff_block_for_a_single_replace() {
+        let workspace = temp_workspace();
+        fs::write(workspace.join("a.txt"), "line1\nline2\nline3\n").unwrap();
+        let ctx = test_ctx(workspace.clone());
+        let args = json!({
+            "path": "a.txt",
+            "old": "line2",
+            "new": "changed",
+            "reason": "test edit"
+        });
+        let result = Edit.run(&ctx, &args).unwrap();
+        assert!(result.contains("```diff"));
+        assert!(result.contains("-line2"));
+        assert!(result.contains("+changed"));
+        fs::remove_dir_all(&workspace).ok();
+    }
+
+    #[test]
+    fn edit_truncates_a_very_large_diff() {
+        let workspace = temp_workspace();
+        let old_content: String = (0..300).map(|i| format!("line{i}\n")).collect();
+        let new_content: String = (0..300).map(|i| format!("changed{i}\n")).collect();
+        fs::write(workspace.join("big.txt"), &old_content).unwrap();
+        let ctx = test_ctx(workspace.clone());
+        let args = json!({
+            "path": "big.txt",
+            "old": &old_content,
+            "new": &new_content,
+            "reason": "test large replace"
+        });
+        let result = Edit.run(&ctx, &args).unwrap();
+        assert!(result.contains("more lines truncated"));
+        fs::remove_dir_all(&workspace).ok();
+    }
+}