json: add parameter to disable sorting

src/std/text/json-test.ss

@@ -17,8 +17,12 @@
   (test-suite "test :std/text/json"
 
     (def (check-encode-decode obj str)
-      (check (call-with-output-string (cut write-json obj <>)) => str)
-      (check (call-with-input-string str read-json) => obj))
+      (parameterize ((json-sort-keys #f))
+        (check (call-with-input-string (call-with-output-string (cut write-json obj <>)) read-json)
+               => obj))
+      (parameterize ((json-sort-keys #t))
+        (check (call-with-output-string (cut write-json obj <>)) => str)
+        (check (call-with-input-string str read-json) => obj)))
 
     (def (check-encode-decode= obj)
       (let (p (open-output-u8vector))

src/std/text/json.ss

@@ -23,7 +23,7 @@
         :std/text/hex)
 (export read-json write-json
         string->json-object json-object->string
-        json-symbolic-keys json-list-wrapper
+        json-symbolic-keys json-list-wrapper json-sort-keys
         write-json-alist write-json-alist/sort json-sort-alist)
 (declare (not safe))
 
@@ -49,6 +49,11 @@
 (def json-list-wrapper
   (make-parameter identity))
 
+;; Should object keys be sorted when writing json?
+;; Checking for duplicate keys only reliably works when this is true.
+(def json-sort-keys
+  (make-parameter #t))
+
 ;;; implementation
 (def (raise-invalid-token port char)
   (if (eof-object? char)
@@ -370,7 +375,10 @@
   (write-json-alist (json-sort-alist alist obj) port obj))
 
 (def (write-json-hash obj port)
-  (write-json-alist/sort (hash->list obj) port obj))
+  (def lst (hash->list obj))
+  (if (json-sort-keys)
+    (write-json-alist/sort lst port obj)
+    (write-json-alist lst port obj)))
 
 (def (write-json-string obj port)
   (def escape