json: tell prettier content is to be parsed as json

In json-mode tell prettier the content is always to be parsed as json.
Fixes formatting in orgmode `#+BEGIN_SRC json` blocks as prettier
otherwise expects content as javascript.

Fixes: #11343

layers/+lang/json/funcs.el

@@ -9,6 +9,12 @@
 ;;
 ;;; License: GPLv3
 
+(defun spacemacs/json-setup-prettier ()
+  "Tell prettier the content is to be parsed as JSON regardless of any file
+extensions."
+  (when (eq json-fmt-tool 'prettier)
+    (setq-local prettier-js-args '("--parser=json"))))
+
 (defun spacemacs/json-navigator-dwim (arg &optional start end)
   "Display the JSON hierarchy of the whole buffer or the active region.
 If ARG is a universal prefix argument then display the hierarchy after point."

layers/+lang/json/packages.el

@@ -32,6 +32,9 @@
   (use-package json-mode
     :defer t))
 
+(defun json/post-init-json-mode ()
+  (add-hook 'json-mode-hook #'spacemacs/json-setup-prettier))
+
 (defun json/init-json-navigator ()
   (use-package json-navigator
     :defer t