Add fixer for json: python's json.tool

Resolves dense-analysis#4314.

Add a fixer that's built into python for json formatting. Include a
couple arguments in docs to make these features more discoverable.

Uses stdin-based fixing so you don't need to save the file to fix.

autoload/ale/fix/registry.vim

@@ -446,6 +446,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['json'],
 \       'description': 'Fix JSON files with jq.',
 \   },
+\   'json_pytool': {
+\       'function': 'ale#fixers#json_pytool#Fix',
+\       'suggested_filetypes': ['json'],
+\       'description': "Fix JSON files with python's built-in json.tool module.",
+\   },
 \   'protolint': {
 \       'function': 'ale#fixers#protolint#Fix',
 \       'suggested_filetypes': ['proto'],

autoload/ale/fixers/json_pytool.vim

@@ -0,0 +1,20 @@
+" Author: idbrii
+" Description: json formatter as ALE fixer using python's json.tool
+
+call ale#Set('json_pytool_executable', 'python')
+call ale#Set('json_pytool_options', '')
+call ale#Set('json_pytool_use_global', get(g:, 'ale_use_global_executables', 0))
+
+function! ale#fixers#json_pytool#GetExecutable(buffer) abort
+    return ale#path#FindExecutable(a:buffer, 'json_pytool', ['python'])
+endfunction
+
+function! ale#fixers#json_pytool#Fix(buffer) abort
+    let l:executable = ale#Escape(ale#fixers#json_pytool#GetExecutable(a:buffer))
+    let l:opts = ale#Var(a:buffer, 'json_pytool_options')
+    let l:command = printf('%s -m json.tool %s -', l:executable, l:opts)
+
+    return {
+    \   'command': l:command
+    \ }
+endfunction

doc/ale-json.txt

@@ -77,6 +77,38 @@ g:ale_json_fixjson_use_global                   *g:ale_json_fixjson_use_global*
   See |ale-integrations-local-executables|
 
 
+===============================================================================
+python's json.tool                                            *ale-json-pytool*
+
+g:ale_json_pytool_executable                   *g:ale_json_pytool_executable*
+                                               *b:ale_json_pytool_executable*
+
+  Type: |String|
+  Default: `'python'`
+
+  The python executable that run to use its json.tool module. This fixer
+  requires python 3, which includes the json module.
+
+g:ale_json_pytool_options                          *g:ale_json_pytool_options*
+                                                   *b:ale_json_pytool_options*
+
+  Type: |String|
+  Default: `''`
+
+  These options are passed to the json.tool module. Example: >
+    let g:ale_json_pytool_options = '--sort-keys --indent 2'
+<  See docs for all options:
+    https://docs.python.org/3/library/json.html#module-json.tool
+
+g:ale_json_pytool_use_global                    *g:ale_json_pytool_use_global*
+                                                *b:ale_json_pytool_use_global*
+
+  Type: |Number|
+  Default: `get(g:, 'ale_use_global_executables', 0)`
+
+  See |ale-integrations-local-executables|
+
+
 ===============================================================================
 jsonlint                                                    *ale-json-jsonlint*
 

doc/ale-supported-languages-and-tools.txt

@@ -317,6 +317,7 @@ Notes:
   * `eslint`
   * `fixjson`
   * `jq`
+  * `json.tool`
   * `jsonlint`
   * `prettier`
   * `spectral`

supported-tools.md

@@ -326,6 +326,7 @@ formatting.
   * [eslint](http://eslint.org/) :warning:
   * [fixjson](https://github.com/rhysd/fixjson)
   * [jq](https://stedolan.github.io/jq/) :warning:
+  * [json.tool](https://docs.python.org/3/library/json.html#module-json.tool) :warning:
   * [jsonlint](https://github.com/zaach/jsonlint)
   * [prettier](https://github.com/prettier/prettier)
   * [spectral](https://github.com/stoplightio/spectral)