bug#31138: Native json slower than json.el

[Sebastien Chapuis]

Hi,

I have tested the new function json-parse-string to use it in lsp-mode
and was suprised when I found out that this function is slower than
json-read-from-string from json.el:

Test with a string of 4042446 characters:
```
json-parse-string:       9,166010 seconds
json-read-from-string:   6.028625 seconds
```

I took a look at the code, and if I remove the call to
code_convert_string in json_make_string (see the attached diff),
it's way faster:

Test with a string of 4042411 characters
```
json-parse-string (without code_convert_string):
0.505582 seconds
```

Is this conversion really necessary ? Should I set some variable to avoid
this ?


By the way, what is the state of this patch:
https://lists.gnu.org/archive/html/emacs-devel/2017-12/msg00916.html
Could it be merge ?

diff --git a/src/json.c b/src/json.c
index b046d34f66..1fc976214d 100644
--- a/src/json.c
+++ b/src/json.c
@@ -219,8 +219,7 @@ json_has_suffix (const char *string, const char *suffix)
 static Lisp_Object
 json_make_string (const char *data, ptrdiff_t size)
 {
-  return code_convert_string (make_specified_string (data, -1, size, false),
-                              Qutf_8_unix, Qt, false, true, true);
+  return make_specified_string (data, -1, size, false);
 }
 
 /* Create a multibyte Lisp string from the null-terminated UTF-8

--
Sebastien Chapuis