json: support for a [required] field attribute (#10955)

vlib/json/json_decode_test.v

@@ -0,0 +1,35 @@
+import json
+
+struct TestTwin {
+	id     int
+	seed   string
+	pubkey string
+}
+
+struct TestTwins {
+mut:
+	twins []TestTwin [required]
+}
+
+fn test_json_decode_fails_to_decode_unrecognised_array_of_dicts() {
+	data := '[{"twins":[{"id":123,"seed":"abcde","pubkey":"xyzasd"},{"id":456,"seed":"dfgdfgdfgd","pubkey":"skjldskljh45sdf"}]}]'
+	json.decode(TestTwins, data) or {
+		assert err.msg == "expected field 'twins' is missing"
+		return
+	}
+	assert false
+}
+
+fn test_json_decode_works_with_a_dict_of_arrays() {
+	data := '{"twins":[{"id":123,"seed":"abcde","pubkey":"xyzasd"},{"id":456,"seed":"dfgdfgdfgd","pubkey":"skjldskljh45sdf"}]}'
+	res := json.decode(TestTwins, data) or {
+		assert false
+		exit(1)
+	}
+	assert res.twins[0].id == 123
+	assert res.twins[0].seed == 'abcde'
+	assert res.twins[0].pubkey == 'xyzasd'
+	assert res.twins[1].id == 456
+	assert res.twins[1].seed == 'dfgdfgdfgd'
+	assert res.twins[1].pubkey == 'skjldskljh45sdf'
+}