Method calculateEdit

packages/core/src/tools/edit.ts:113–216

* Calculates the potential outcome of an edit operation. * @param params Parameters for the edit operation * @returns An object describing the potential edit outcome * @throws File system errors if reading the file fails unexpectedly (e.g., permissions)

(
    params: EditToolParams,
    abortSignal: AbortSignal,
  )

   * @throws File system errors if reading the file fails unexpectedly (e.g., permissions)
   */
  private async calculateEdit(
    params: EditToolParams,
    abortSignal: AbortSignal,
  ): Promise<CalculatedEdit> {
    const expectedReplacements = params.expected_replacements ?? 1;
    let currentContent: string | null = null;
    let fileExists = false;
    let isNewFile = false;
    let finalNewString = params.new_string;
    let finalOldString = params.old_string;
    let occurrences = 0;
    let error:
      | { display: string; raw: string; type: ToolErrorType }
      | undefined = undefined;

    try {
      currentContent = fs.readFileSync(params.file_path, 'utf8');
      // Normalize line endings to LF for consistent processing.
      currentContent = currentContent.replace(/\r\n/g, '\n');
      fileExists = true;
    } catch (err: unknown) {
      if (!isNodeError(err) || err.code !== 'ENOENT') {
        // Rethrow unexpected FS errors (permissions, etc.)
        throw err;
      }
      fileExists = false;
    }

    if (params.old_string === '' && !fileExists) {
      // Creating a new file
      isNewFile = true;
    } else if (!fileExists) {
      // Trying to edit a nonexistent file (and old_string is not empty)
      error = {
        display: `File not found. Cannot apply edit. Use an empty old_string to create a new file.`,
        raw: `File not found: ${params.file_path}`,
        type: ToolErrorType.FILE_NOT_FOUND,
      };
    } else if (currentContent !== null) {
      // Editing an existing file
      const correctedEdit = await ensureCorrectEdit(
        params.file_path,
        currentContent,
        params,
        this.config.getAnusClient(),
        abortSignal,
      );
      finalOldString = correctedEdit.params.old_string;
      finalNewString = correctedEdit.params.new_string;
      occurrences = correctedEdit.occurrences;

      if (params.old_string === '') {
        // Error: Trying to create a file that already exists
        error = {
          display: `Failed to edit. Attempted to create a file that already exists.`,
          raw: `File already exists, cannot create: ${params.file_path}`,
          type: ToolErrorType.ATTEMPT_TO_CREATE_EXISTING_FILE,
        };