[json] Add option to format on save

CHANGELOG.develop

@@ -1773,6 +1773,8 @@ Other:
 - Added missing optional argument for the =jabber-alert-echo= function to fix
   =wrong-number-of-arguments= error when jabber receives a new notification
   (thanks to Aleksei Fedotov)
+**** Json
+- Added variable =json-fmt-on-save= to run the selected formatter on save.
 **** Jsonnet
 - Fixed flycheck support in jsonnet files (thanks to Vikash Balasubramanian)
 **** Java

layers/+lang/json/README.org

@@ -61,6 +61,13 @@ Formatter can be chosen on a per project basis using directory local variables
 
 *Note:* you can easily add a directory local variable with ~SPC f v d~.
 
+** Formatting on save
+To enable using the selected formatter on save, set the layer variable =json-fmt-on-save=:
+
+#+BEGIN_SRC elisp
+  (json :variables json-fmt-on-save t)
+#+END_SRC
+
 * Usage
 ** Reformat
 ~SPC m =~ will reformat the whole buffer or the active region. Use numerical

layers/+lang/json/config.el

@@ -13,3 +13,6 @@
 
 (defvar json-fmt-tool 'web-beautify
   "The formatter to format a JSON file. Possible values are `web-beautify' and `prettier'.")
+
+(defvar json-fmt-on-save nil
+  "Run formatter on buffer save.")

layers/+lang/json/packages.el

@@ -58,9 +58,15 @@
 (defun json/pre-init-prettier-js ()
   (when (eq json-fmt-tool 'prettier)
     (add-to-list 'spacemacs--prettier-modes 'json-mode)
-    (add-hook 'json-mode-hook #'spacemacs/json-setup-prettier)))
+    (add-hook 'json-mode-hook #'spacemacs/json-setup-prettier)
+    (when (eq json-fmt-on-save t)
+      (add-hook 'json-mode-hook 'prettier-js-mode))))
 
 (defun json/pre-init-web-beautify ()
   (when (eq json-fmt-tool 'web-beautify)
     (add-to-list 'spacemacs--web-beautify-modes
-                 (cons 'json-mode 'web-beautify-js))))
+                 (cons 'json-mode 'web-beautify-js))
+    (when (eq json-fmt-on-save t)
+      (add-hook 'json-mode-hook
+                (lambda ()
+                  (add-hook 'before-save-hook 'web-beautify-js-buffer t t))))))