bug#43016: replace-region-contents takes a lot of time when called from json-pretty-print-buffer

[ljell]

>
> If you run M-x json-pretty-print-buffer on the already pretty file then it's 
> much faster,so maybe it's related to the single long line generated by 
> json-encode.


The json-encode part was missing in my first post, so the relevant code looks 
like this:

...
  (with-temp-buffer
    (insert (json-encode data))
    (json-pretty-print-buffer)
    (write-file "data.json"))
...


So I insert json encoded lisp data into a temp buffer and then run prettyfing 
on it, so the json file is more readable and there are no long lines. This code 
took a few seconds on 26 and it takes much longer with 27.