How to pretty-format code (auto-insert newlines, indent, etc)?

Question

I'm using spacemacs but presumably it's emacs knowledge that's required here.

I have a JSON file with a single long line, let's say this JSON from json.org/example:

{"menu": {"id": "file", "value": "File", "popup": {"menuitem": [{"value": "New", "onclick": "CreateNewDoc()"}, {"value": "Open", "onclick": "OpenDoc()"}, {"value": "Close", "onclick": "CloseDoc()"}]}}}

I would like emacs to reindent this, which means to me not change the leftmost character of line to the proper indentation level, but break the line in several lines.

If I use spacemacs/indent-region-or-buffer (SPC j =) then the text is not changed at all.

How could I ask from emacs to actually break this long line and reindent to get something like this:

{"menu": {
  "id": "file",
  "value": "File",
  "popup": {
    "menuitem": [
      {"value": "New", "onclick": "CreateNewDoc()"},
      {"value": "Open", "onclick": "OpenDoc()"},
      {"value": "Close", "onclick": "CloseDoc()"}
    ]
  }
}}

I'm not interested in a JSON-specific answer, for instance I believe that intelliJ does that for any language it supports (java, json...). I would think it's achievable for any language emacs has a major mode for, or let's say the most popular ones.

EDIT I discovered M-x json-reformat-region that spacemacs ships with and works, but yes, I would like that for any language and with always the same shortcut, based on the major mode...

EDIT2 Ok so my conclusion is that it's implemented for various languages, JSON & lisp at least, presumably others, and it would be easy for yet more (XML/XHTML, go which has go-fmt and also using clang). However there's no generic function name that would do it for all the languages. There is space here to implement it in spacemacs layers for the various languages... I didn't find a X/HTML implementation though, which surprises me a bit.

yang xun · Answer

I use json-mode-beautify
GNU Emacs 24.3.1
;;; json-mode.el --- Major mode for editing JSON files.

;; Author: Josh Johnston
;; URL: https://github.com/joshwnj/json-mode
;; Version: 1.6.0

ninrod · Answer

With emacs 26.3 you can just use the stock json-pretty-print function.

json-pretty-print is an interactive and compiled function defined in
  json.el.gz.
  
  -- Emacs 26.3 documentation

select the region and M-x json-pretty-print.

I've just executed this procedure taking your example as input. Here is the result:

{
  "menu": {
    "id": "file",
    "value": "File",
    "popup": {
      "menuitem": [
        {
          "value": "New",
          "onclick": "CreateNewDoc()"
        },
        {
          "value": "Open",
          "onclick": "OpenDoc()"
        },
        {
          "value": "Close",
          "onclick": "CloseDoc()"
        }
      ]
    }
  }
}

Stefan · Answer

BTW, for major modes using SMIE as their indentation engine, there is some part of what you need for that in the form of an auto-fill-mode support. I think fill-paragraph or fill-region won't do a good job, but if you put your code onto a single line, then go to the end of that line and do M-: (smie-auto-fill) it should give sane results (probably not perfect by a long stretch, tho).

Answered by Stefan on November 18, 2021

Fergie · Answer

For this specific scenario json-pretty-print will prettify the highlighted lump of json.

wvxvw · Answer

json.el package provides json-pretty-print-buffer.  This is what it produces for your example:

{
  "menu": {
    "popup": {
      "menuitem": [
        {
          "onclick": "CreateNewDoc()",
          "value": "New"
        },
        {
          "onclick": "OpenDoc()",
          "value": "Open"
        },
        {
          "onclick": "CloseDoc()",
          "value": "Close"
        }
      ]
    },
    "value": "File",
    "id": "file"
  }
}

Seems pretty decent to me.

Tu Do · Answer

According to the tip here, you can use external command to format a region in your Json file:

(defun json-format ()
  (interactive)
  (save-excursion
    (shell-command-on-region (region-beginning)
                             (region-end)
                             "python -m json.tool"
                             (buffer-name)
                             t)))

You can easily extend it to format the whole buffer:

(defun json-format ()
  (interactive)
  (save-excursion
    (shell-command-on-region (point-min)
                             (point-max)
                             "python -m json.tool"
                             (buffer-name) t)))

Emacs does not have formatting tool for programming languages (except for Lisp), only indentation commands.

Kaushal Modi · Answer

It looks like you need the fill-region function more than the indentation.

Select that line and do M-x fill-region. 
Select the same, now split across multiple lines, and do M-x indent-region.

That will, though, not insert new lines at the exact points as shown in your example. It will simply make the line fit in the fill columns.

How to pretty-format code (auto-insert newlines, indent, etc)?

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