Function loadDiffData

src/components/FileEditToolDiff.tsx:64–120

(file_path: string, edits: FileEdit[])

}

async function loadDiffData(file_path: string, edits: FileEdit[]): Promise<DiffData> {
  const valid = edits.filter(e => e.old_string != null && e.new_string != null);
  const single = valid.length === 1 ? valid[0]! : undefined;

  // SedEditPermissionRequest passes the entire file as old_string. Scanning for
  // a needle ≥ CHUNK_SIZE allocates O(needle) for the overlap buffer — skip the
  // file read entirely and diff the inputs we already have.
  if (single && single.old_string.length >= CHUNK_SIZE) {
    return diffToolInputsOnly(file_path, [single]);
  }

  try {
    const handle = await openForScan(file_path);
    if (handle === null) return diffToolInputsOnly(file_path, valid);
    try {
      // Multi-edit and empty old_string genuinely need full-file for sequential
      // replacements — structuredPatch needs before/after strings. replace_all
      // routes through the chunked path below (shows first-occurrence window;
      // matches within the slice still replace via edit.replace_all).
      if (!single || single.old_string === '') {
        const file = await readCapped(handle);
        if (file === null) return diffToolInputsOnly(file_path, valid);
        const normalized = valid.map(e => normalizeEdit(file, e));
        return {
          patch: getPatchForDisplay({
            filePath: file_path,
            fileContents: file,
            edits: normalized,
          }),
          firstLine: firstLineOf(file),
          fileContent: file,
        };
      }

      const ctx = await scanForContext(handle, single.old_string, CONTEXT_LINES);
      if (ctx.truncated || ctx.content === '') {
        return diffToolInputsOnly(file_path, [single]);
      }
      const normalized = normalizeEdit(ctx.content, single);
      const hunks = getPatchForDisplay({
        filePath: file_path,
        fileContents: ctx.content,
        edits: [normalized],
      });
      return {
        patch: adjustHunkLineNumbers(hunks, ctx.lineOffset - 1),
        firstLine: ctx.lineOffset === 1 ? firstLineOf(ctx.content) : null,
        fileContent: ctx.content,
      };
    } finally {
      await handle.close();
    }
  } catch (e) {
    logError(e as Error);
    return diffToolInputsOnly(file_path, valid);
  }
}