Allow any JSON value at the top level (Bug#42994).

Newer standards like RFC 8259, which obsoletes the earlier RFC 4627,
now allow any top-level value unconditionally, so Emacs should too.

* src/json.c (Fjson_serialize, Fjson_insert): Pass JSON_ENCODE_ANY to
allow serialization of any JSON value.  Call 'lisp_to_json' instead of
'lisp_to_json_toplevel'.  Remove obsolete comments
(neither JSON_DECODE_ANY nor JSON_ALLOW_NUL are allowed here).  Reword
documentation strings.
(Fjson_parse_string, Fjson_parse_buffer): Pass JSON_DECODE_ANY to
allow deserialization of any JSON value.  Reword documentation
strings.
(lisp_to_json_nonscalar, lisp_to_json_nonscalar_1): Rename from
"toplevel" to avoid confusion.
(lisp_to_json): Adapt caller.
* test/src/json-tests.el (json-serialize/roundtrip-scalars): New unit
test.
* doc/lispref/text.texi (Parsing JSON): Update documentation.

1 files changed, 28 insertions, 0 deletions

diff --git a/test/src/json-tests.el b/test/src/json-tests.el
index 4be11b8c81a..908945fcb08 100644
--- a/test/src/json-tests.el
+++ b/test/src/json-tests.el
@@ -51,6 +51,34 @@
       (should (equal (json-parse-buffer) lisp))
       (should (eobp)))))
 
+(ert-deftest json-serialize/roundtrip-scalars ()
+  "Check that Bug#42994 is fixed."
+  (skip-unless (fboundp 'json-serialize))
+  (dolist (case '((:null "null")
+                  (:false "false")
+                  (t "true")
+                  (0 "0")
+                  (123 "123")
+                  (-456 "-456")
+                  (3.75 "3.75")
+                  ;; The noncharacter U+FFFF should be passed through,
+                  ;; cf. https://www.unicode.org/faq/private_use.html#noncharacters.
+                  ("abc\uFFFFαβγ𝔸𝐁𝖢\"\\"
+                   "\"abc\uFFFFαβγ𝔸𝐁𝖢\\\"\\\\\"")))
+    (cl-destructuring-bind (lisp json) case
+      (ert-info ((format "%S ↔ %S" lisp json))
+        (should (equal (json-serialize lisp) json))
+        (with-temp-buffer
+          (json-insert lisp)
+          (should (equal (buffer-string) json))
+          (should (eobp)))
+        (should (equal (json-parse-string json) lisp))
+        (with-temp-buffer
+          (insert json)
+          (goto-char 1)
+          (should (equal (json-parse-buffer) lisp))
+          (should (eobp)))))))
+
 (ert-deftest json-serialize/object ()
   (skip-unless (fboundp 'json-serialize))
   (let ((table (make-hash-table :test #'equal)))