Accept alists when serializing JSON

* src/json.c (lisp_to_json_toplevel_1): Also accept alists
representing objects.

* src/json.c (Fjson_serialize): Update docstring.

* test/src/json-tests.el (json-serialize/object): Add unit tests for
serializing alists.

* doc/lispref/text.texi (Parsing JSON): Document that serialization
functions accept alists.

1 files changed, 6 insertions, 4 deletions

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 561ad804344..7a1983641fd 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -4929,14 +4929,16 @@ represented using Lisp vectors.
 
 @item
 JSON has only one map type, the object.  JSON objects are represented
-using Lisp hashtables or alists.
+using Lisp hashtables or alists.  When an alist contains several
+elements with the same key, Emacs uses only the first element for
+serialization, in accordance with the behavior of @code{assq}.
 
 @end itemize
 
 @noindent
-Note that @code{nil} represents the empty JSON object, @code{@{@}},
-not @code{null}, @code{false}, or an empty array, all of which are
-different JSON values.
+Note that @code{nil} is a valid alist and represents the empty JSON
+object, @code{@{@}}, not @code{null}, @code{false}, or an empty array,
+all of which are different JSON values.
 
   If some Lisp object can't be represented in JSON, the serialization
 functions will signal an error of type @code{wrong-type-argument}.