Improve error reporting when serializing non-Unicode strings to JSON

* src/coding.c (utf8_string_p): New helper function.
(syms_of_coding) <utf-8-unix>: Move from json.c.

* src/json.c (json_check_utf8): New helper function.
(lisp_to_json_toplevel_1, lisp_to_json): Use it.  To save a bit of
time, check for invalid UTF-8 strings only after encountering an
error, since Jansson already rejects them.

* test/src/json-tests.el (json-serialize/invalid-unicode): Adapt
expected error symbol.

1 files changed, 5 insertions, 7 deletions

diff --git a/test/src/json-tests.el b/test/src/json-tests.el
index e394583bc76..107cab89083 100644
--- a/test/src/json-tests.el
+++ b/test/src/json-tests.el
@@ -108,13 +108,11 @@
 
 (ert-deftest json-serialize/invalid-unicode ()
   (skip-unless (fboundp 'json-serialize))
-  ;; FIXME: "out of memory" is the wrong error signal, but we don't
-  ;; currently distinguish between error types when serializing.
-  (should-error (json-serialize ["a\uDBBBb"]) :type 'json-out-of-memory)
-  (should-error (json-serialize ["u\x110000v"]) :type 'json-out-of-memory)
-  (should-error (json-serialize ["u\x3FFFFFv"]) :type 'json-out-of-memory)
-  (should-error (json-serialize ["u\xCCv"]) :type 'json-out-of-memory)
-  (should-error (json-serialize ["u\u00C4\xCCv"]) :type 'json-out-of-memory))
+  (should-error (json-serialize ["a\uDBBBb"]) :type 'wrong-type-argument)
+  (should-error (json-serialize ["u\x110000v"]) :type 'wrong-type-argument)
+  (should-error (json-serialize ["u\x3FFFFFv"]) :type 'wrong-type-argument)
+  (should-error (json-serialize ["u\xCCv"]) :type 'wrong-type-argument)
+  (should-error (json-serialize ["u\u00C4\xCCv"]) :type 'wrong-type-argument))
 
 (ert-deftest json-parse-string/null ()
   (skip-unless (fboundp 'json-parse-string))