json - Emacs 中类似模型/ View 的编辑

Question

我有一些 JSON 文件，我正在编写一种模式，允许独立于其余部分编辑 JSON 对象的单个属性。例如:

foo.json:

{
  "creation_timestamp": "1411210038.000000",
  "description": "lorem ipsum.\ndolor sit amet.",
  "version": 4
}

打开 foo.json 会产生这个缓冲区:

lorem ipsum.

dolor sit amet.

将第一行更改为“foo bar”并保存文件会导致 foo.json只有 description字段更新:

{
  "creation_timestamp": "1411210038.000000",
  "description": "foo bar.\ndolor sit amet.",
  "version": 4
}

最好的策略是什么？我目前的尝试是这样的:

使用 find-file

打开 JSON 文件

创建从最小点到最大点的不可见覆盖

解析 json

插入 description 的值点属性，创建“ View ”

添加本地写入文件 Hook 和保存后 Hook

local-write-file钩子(Hook)杀死“ View ”，更新覆盖中的json，并保存文件。 after-save钩子(Hook)重新创建“ View ”，以便用户可以继续编辑。

这是冗长而脆弱的。有没有更好的方法来处理屏幕表示应该不同于磁盘表示的数据？

Answer 1

您可以在 format-alist 中定义自己的编码和解码。为了这个目的。
您的示例可以通过以下方式实现:

(defvar-local my-head nil
  "Header of json file cut off by json-descr format.")

(defvar-local my-tail nil
  "Tail of json file cut off by json-descr format.")

(defun my-from-fn (BEGIN END)
  "`format-alist'"
  (save-restriction
    (narrow-to-region BEGIN END)
    (goto-char (point-min))
    (let* ((b (re-search-forward "^[[:blank:]]*\"description\":[[:blank:]]*\"" nil t))
       (e (ignore-errors (1- (scan-sexps (1- b) 1)))))
      (unless (and b e)
    (error "Error in original mode")) ;;< TODO some more sensible error message
      ;; Save head and tail and delete corresponding buffer regions:
      (setq-local my-head (buffer-substring-no-properties (point-min) b))
      (setq-local my-tail (buffer-substring-no-properties e (point-max)))
      (delete-region e (point-max))
      (delete-region (point-min) b)
      ;; Formatting:
      (goto-char (point-min))
      (while (search-forward "\\n" nil t)
    (replace-match "\n"))
      )
    (point-max) ;;< required by `format-alist'
    ))

(defun my-to-fn (BEGIN END BUFFER)
  "`format-alist'"
  (save-restriction
    (narrow-to-region BEGIN END)
    ;; Formatting:
    (goto-char (point-min))
    (while (search-forward "\n" nil t)
      (replace-match "\\\\n"))
    ;; Insert head and tail:
    (let ((head (with-current-buffer BUFFER my-head))
      (tail (with-current-buffer BUFFER my-tail)))
      (goto-char (point-min))
      (insert head)
      (goto-char (point-max))
      (insert tail))
    (point-max)))

(add-to-list 'format-alist
         '(json-descr
           "File format for editing a single property of a json object."
           nil
           my-from-fn
           my-to-fn
           t ; MODIFY: my-to-fn modifies the buffer
           nil
           nil))

(define-derived-mode my-mode fundamental-mode "JDescr"
  "Major mode for editing json description properties."
  (format-decode-buffer 'json-descr))

实际上，也可以将其解释为更普遍的问题。将文件加载到隐藏缓冲区中。使用另一个可见缓冲区来编辑其转换后的内容。在保存可见缓冲区时，实际上将内容转换回原始格式并保存隐藏缓冲区。

我现在没有时间实现上述一般情况。
以下代码大致涵盖了您的特殊情况。 (请注意，这是一个快速破解，仅用于演示目的。)

(defvar-local original-mode-other nil
  "Other buffer related to the current one.")


(define-derived-mode original-mode special-mode ""
  "Opens file in invisible auxiliary buffer."
  (let* ((b (re-search-forward "^[[:blank:]]*\"description\":[[:blank:]]*\"" nil t))
     (e (ignore-errors (1- (scan-sexps (1- b) 1))))
     (original-name (buffer-name))
     (original-buffer (current-buffer))
     str)
    (unless (and b e)
      (error "Error in original mode")) ;; TODO some more sensible error message
    (narrow-to-region b e)
    (setq str (buffer-substring-no-properties b e))
    (rename-buffer (concat " *" original-name))
    (with-current-buffer (switch-to-buffer (get-buffer-create original-name))
      ;; Set-up the clone buffer for editing the transformed content:
      (set-visited-file-name (buffer-file-name original-buffer) t)
      (setq original-mode-other original-buffer)
      (insert str)
      (set-buffer-modified-p nil)
      ;; Transform content to the format of the clone buffer:
      (goto-char (point-min))
      (while (search-forward "\\n" nil t) ;; TODO: Skip escaped \n.
    (replace-match "\n"))
      (add-to-list 'write-contents-functions  (lambda ()
                        ;; Transfer content to original buffer
                        (let ((str (buffer-substring-no-properties (point-min) (point-max))))
                          (with-current-buffer original-mode-other
                            (let ((inhibit-read-only t))
                              (delete-region (point-min) (point-max))
                              (insert str)
                              (goto-char (point-min))
                              ;; Transform content to the format of the original buffer:
                              (while (search-forward "\n" nil t)
                            (replace-match "\\\\n"))
                              (save-buffer)
                              )))
                        (set-buffer-modified-p nil)
                        t))
      (add-hook 'kill-buffer-hook (lambda ()
                    (kill-buffer original-mode-other)) t t)
      )))