Why does Sublime Text 3 allow comments in JSON configuration files?

Question

Using comments in JSON configuration files in Sublime Text can make JSON objects unable to be decoded. Here is my story.

I newly installed SublimeREPL plugin in my Sublime Text 3. Soon I discovered it ran Python2.7 instead of 3.5 in default, so I added my own Python3.5 configuration files according to SublimeREPL Docs to make it support Python3.5.

My Packages/SublimeREPL/config/Python3.5/Main.sublime-menu JSON config file looks like this:

[
 {
    "id": "tools",
    "children":
    [{
        "caption": "SublimeREPL",
        "mnemonic": "R",
        "id": "SublimeREPL",
        "children":
        [
            {"caption": "Python3.5",
            "id": "Python3.5",

             "children":[
                {"command": "repl_open",
                 "caption": "Python3.5",
                 "id": "repl_python3.5",
                 "mnemonic": "P",
                 "args": {
                    "type": "subprocess",
                    "encoding": "utf8",
                    "cmd": ["python3", "-i", "-u"],
                    "cwd": "$file_path",
                    "syntax": "Packages/Python/Python.tmLanguage",
                    "external_id": "python3",
                    "extend_env": {"PYTHONIOENCODING": "utf-8"}
                    }
                },
                // run files
                {"command": "repl_open",
                 "caption": "Python3.5 - RUN current file",
                 "id": "repl_python3.5_run",
                 "mnemonic": "R",
                 "args": {
                    "type": "subprocess",
                    "encoding": "utf8",
                    "cmd": ["python3", "-u", "$file_basename"],
                    "cwd": "$file_path",
                    "syntax": "Packages/Python/Python.tmLanguage",
                    "external_id": "python3",
                    "extend_env": {"PYTHONIOENCODING": "utf-8"}
                    }
                }
            ]}
        ]
    }]
}]

Note there is a comment // run files in this file. This config works fine from the menu bar tools->SublimeREPL->Python3.5. However,when I tried to bind the F5 key with repl_python3.5_run to have easier access to 3.5,the following exception was thrown in the console:

Traceback (most recent call last):

  File "./python3.3/json/decoder.py", line 367, in raw_decode
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

File "/opt/sublime_text/sublime_plugin.py", line 551, in run_
    return self.run(**args)

File "/home/ubuntu/.config/sublime-text-3/Packages/SublimeREPL/run_existing_command.py", line 32, in run
    json_cmd = self._find_cmd(id, path)

File "/home/ubuntu/.config/sublime-text-3/Packages/SublimeREPL/run_existing_command.py", line 41, in _find_cmd
    return self._find_cmd_in_file(id, file)

 File "/home/ubuntu/.config/sublime-text-3/Packages/SublimeREPL/run_existing_command.py", line 53, in _find_cmd_in_file
    data = json.loads(bytes)

 File "./python3.3/json/__init__.py", line 316, in loads

 File "./python3.3/json/decoder.py", line 351, in decode

 File "./python3.3/json/decoder.py", line 369, in raw_decode

ValueError: No JSON object could be decoded

After I removed the // run files comment. The F5 key works fine.It's exactly the comment that causes the problem. Sublime Text uses JSON as config files,lots of config files come with // style comments. As we know, comments are removed from JSON by design.

Then how can sublime text allow comments in config files, is it using a pipe? If it is, how can my key binding fail?

**PLEASE DO NOT POST TEXT AS IMAGES**. Copy and paste the text into your question. Images are not searchable, and can not be interpreted by screen readers for those with visual impairments. Use the [edit] link to modify your question. See [this](http://meta.stackoverflow.com/a/285557/1426065) for more information. — MattDMo, Jul 24 '16 at 14:11
You are right.I already corrected my mistake.Thank you for pointing it out.@MattDMo — Naomi, Jul 25 '16 at 05:06

score 3 · Accepted Answer · answered Jul 24 '16 at 14:34

Sublime itself (the core program, not plugins like SublimeREPL) uses an internal JSON library for parsing config files like .sublime-settings, .sublime-menu, .sublime-build, etc. This (most likely customized) parser allows comments.

However, plugins are run through a version of Python (currently 3.3.6 for the dev builds) linked to the Sublime plugin_host executable. Any plugin that imports the standard library's json module (such as run_existing_command.py has to obey the restrictions of that module, and that includes failing to recognize JavaScript-style comments like // in JSON.

One workaround to this would be to import an external module like commentjson that strips various types of comments, including //, before passing the data on to the standard json module. Since it is a pure Python module, you could just copy the source directory into the main SublimeREPL dir, then edit run_existing_command.py appropriately - change line 6 to import commentjson as json and you're all set.

In ST3 you can access the internal library und decode a json string with the `sublime.decode_value(string)` function. — r-stein, Jul 24 '16 at 18:15
@r-stein interesting, I've never looked at that function before. Unfortunately, SublimeREPL seems to have been abandoned some time ago, and while it still works well, the chances of any new features or bugfixes are between slim and none. — MattDMo, Jul 24 '16 at 19:57
Thanks.It sounds like an interesting solution.I will give it a shot. @MattDMo — Naomi, Jul 25 '16 at 08:36

Why does Sublime Text 3 allow comments in JSON configuration files?

1 Answers1