_json returns a different result vs ::parse

[stevenimle-honeywell]

When using const nlohmann::json j{R"([...])"_json}; a different result is returned compared to const nlohmann::json j = nlohmann::json::parse(R"([...])");

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?
  This issue was only reproducible on Ubuntu 18.04 and it did not happen on macOS 10.13.3.

const nlohmann::json body_json{R"([
    {
        "AuthMode": "",
        "Certificate": "",
        "CertificateType": "",
        "Credential": "",
        "CredentialType": "",
        "Password": "password",
        "Path": "{\n  \"clientId\" : \"9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba\",\n  \"service\" : \"rabbitmq\",\n  \"enabled\" : true,\n  \"protocol\" : \"amqp\",\n  \"created\" : \"2018-06-14T17:44:05Z\",\n  \"updated\" : \"2018-06-14T17:44:05Z\",\n  \"connections\" : [ {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"exchange\",\n    \"value\" : \"0\"\n  }, {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"queue\",\n    \"value\" : \"device\"\n  } ]\n}",
        "ServerType": "RabbitMQ",
        "UseExistingConnection": true,
        "UserName": "9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba"
    }
])"_json};

const nlohmann::json body_json = nlohmann::json::parse(R"([
    {
        "AuthMode": "",
        "Certificate": "",
        "CertificateType": "",
        "Credential": "",
        "CredentialType": "",
        "Password": "password",
        "Path": "{\n  \"clientId\" : \"9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba\",\n  \"service\" : \"rabbitmq\",\n  \"enabled\" : true,\n  \"protocol\" : \"amqp\",\n  \"created\" : \"2018-06-14T17:44:05Z\",\n  \"updated\" : \"2018-06-14T17:44:05Z\",\n  \"connections\" : [ {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"exchange\",\n    \"value\" : \"0\"\n  }, {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"queue\",\n    \"value\" : \"device\"\n  } ]\n}",
        "ServerType": "RabbitMQ",
        "UseExistingConnection": true,
        "UserName": "9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba"
    }
])");

Both of these parse correctly in macOS to the following value:

[
  {
    "AuthMode": "",
    "Certificate": "",
    "CertificateType": "",
    "Credential": "",
    "CredentialType": "",
    "Password": "password",
    "Path": "{\n  \"clientId\" : \"9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba\",\n  \"service\" : \"rabbitmq\",\n  \"enabled\" : true,\n  \"protocol\" : \"amqp\",\n  \"created\" : \"2018-06-14T17:44:05Z\",\n  \"updated\" : \"2018-06-14T17:44:05Z\",\n  \"connections\" : [ {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"exchange\",\n    \"value\" : \"0\"\n  }, {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"queue\",\n    \"value\" : \"device\"\n  } ]\n}",
    "ServerType": "RabbitMQ",
    "UseExistingConnection": true,
    "UserName": "9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba"
  }
]

The example using ::parse correctly parses to the above value in Ubuntu 18.04, however, the _json implementation parses to the following:

[
  [
    {
      "AuthMode": "",
      "Certificate": "",
      "CertificateType": "",
      "Credential": "",
      "CredentialType": "",
      "Password": "password",
      "Path": "{\n  \"clientId\" : \"9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba\",\n  \"service\" : \"rabbitmq\",\n  \"enabled\" : true,\n  \"protocol\" : \"amqp\",\n  \"created\" : \"2018-06-14T17:44:05Z\",\n  \"updated\" : \"2018-06-14T17:44:05Z\",\n  \"connections\" : [ {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"exchange\",\n    \"value\" : \"0\"\n  }, {\n    \"host\" : \"127.0.0.1\",\n    \"port\" : 5672,\n    \"virtualHost\" : \"/\",\n    \"type\" : \"queue\",\n    \"value\" : \"device\"\n  } ]\n}",
      "ServerType": "RabbitMQ",
      "UseExistingConnection": true,
      "UserName": "9dfeaea7-7d3f-4ce9-b4ac-e17badddf2ba"
    }
  ]
]

Compiler Version:
g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0
Currently not listed as supported.

Library Version: 3.1.2 (release)

Testing
Dockerfile used to run the unit tests:

FROM ubuntu:18.04

ENV HOME /root

ENV DEBIAN_FRONTEND noninteractive
RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections

RUN apt-get update
RUN apt-get install -y software-properties-common cmake git build-essential curl libcurl4-openssl-dev libssl-dev uuid-dev zlib1g-dev librabbitmq-dev

RUN git clone -b v3.1.2 https://github.com/nlohmann/json.git

WORKDIR json/build

RUN cmake ..
RUN cmake --build .

ENTRYPOINT ctest --output-on-failure

Test project /json/build
      Start  1: test-algorithms_default
 1/78 Test  #1: test-algorithms_default .............   Passed    0.01 sec
      Start  2: test-algorithms_all
 2/78 Test  #2: test-algorithms_all .................   Passed    0.00 sec
      Start  3: test-allocator_default
 3/78 Test  #3: test-allocator_default ..............   Passed    0.00 sec
      Start  4: test-allocator_all
 4/78 Test  #4: test-allocator_all ..................   Passed    0.00 sec
      Start  5: test-alt-string_default
 5/78 Test  #5: test-alt-string_default .............   Passed    0.00 sec
      Start  6: test-alt-string_all
 6/78 Test  #6: test-alt-string_all .................   Passed    0.00 sec
      Start  7: test-capacity_default
 7/78 Test  #7: test-capacity_default ...............   Passed    0.01 sec
      Start  8: test-capacity_all
 8/78 Test  #8: test-capacity_all ...................   Passed    0.01 sec
      Start  9: test-cbor_default
 9/78 Test  #9: test-cbor_default ...................   Passed    1.61 sec
      Start 10: test-cbor_all
10/78 Test #10: test-cbor_all .......................   Passed   24.93 sec
      Start 11: test-class_const_iterator_default
11/78 Test #11: test-class_const_iterator_default ...   Passed    0.00 sec
      Start 12: test-class_const_iterator_all
12/78 Test #12: test-class_const_iterator_all .......   Passed    0.00 sec
      Start 13: test-class_iterator_default
13/78 Test #13: test-class_iterator_default .........   Passed    0.00 sec
      Start 14: test-class_iterator_all
14/78 Test #14: test-class_iterator_all .............   Passed    0.00 sec
      Start 15: test-class_lexer_default
15/78 Test #15: test-class_lexer_default ............   Passed    0.00 sec
      Start 16: test-class_lexer_all
16/78 Test #16: test-class_lexer_all ................   Passed    0.00 sec
      Start 17: test-class_parser_default
17/78 Test #17: test-class_parser_default ...........   Passed    0.08 sec
      Start 18: test-class_parser_all
18/78 Test #18: test-class_parser_all ...............   Passed    0.08 sec
      Start 19: test-comparison_default
19/78 Test #19: test-comparison_default .............   Passed    0.01 sec
      Start 20: test-comparison_all
20/78 Test #20: test-comparison_all .................   Passed    0.01 sec
      Start 21: test-concepts_default
21/78 Test #21: test-concepts_default ...............   Passed    0.00 sec
      Start 22: test-concepts_all
22/78 Test #22: test-concepts_all ...................   Passed    0.00 sec
      Start 23: test-constructor1_default
23/78 Test #23: test-constructor1_default ...........   Passed    0.04 sec
      Start 24: test-constructor1_all
24/78 Test #24: test-constructor1_all ...............   Passed    0.03 sec
      Start 25: test-constructor2_default
25/78 Test #25: test-constructor2_default ...........   Passed    0.00 sec
      Start 26: test-constructor2_all
26/78 Test #26: test-constructor2_all ...............   Passed    0.00 sec
      Start 27: test-convenience_default
27/78 Test #27: test-convenience_default ............   Passed    0.00 sec
      Start 28: test-convenience_all
28/78 Test #28: test-convenience_all ................   Passed    0.00 sec
      Start 29: test-conversions_default
29/78 Test #29: test-conversions_default ............   Passed    0.03 sec
      Start 30: test-conversions_all
30/78 Test #30: test-conversions_all ................   Passed    0.03 sec
      Start 31: test-deserialization_default
31/78 Test #31: test-deserialization_default ........   Passed    0.01 sec
      Start 32: test-deserialization_all
32/78 Test #32: test-deserialization_all ............   Passed    0.01 sec
      Start 33: test-element_access1_default
33/78 Test #33: test-element_access1_default ........   Passed    0.01 sec
      Start 34: test-element_access1_all
34/78 Test #34: test-element_access1_all ............   Passed    0.01 sec
      Start 35: test-element_access2_default
35/78 Test #35: test-element_access2_default ........   Passed    0.02 sec
      Start 36: test-element_access2_all
36/78 Test #36: test-element_access2_all ............   Passed    0.02 sec
      Start 37: test-inspection_default
37/78 Test #37: test-inspection_default .............   Passed    4.69 sec
      Start 38: test-inspection_all
38/78 Test #38: test-inspection_all .................   Passed    4.65 sec
      Start 39: test-items_default
39/78 Test #39: test-items_default ..................   Passed    0.01 sec
      Start 40: test-items_all
40/78 Test #40: test-items_all ......................   Passed    0.01 sec
      Start 41: test-iterators1_default
41/78 Test #41: test-iterators1_default .............   Passed    0.02 sec
      Start 42: test-iterators1_all
42/78 Test #42: test-iterators1_all .................   Passed    0.02 sec
      Start 43: test-iterators2_default
43/78 Test #43: test-iterators2_default .............   Passed    0.04 sec
      Start 44: test-iterators2_all
44/78 Test #44: test-iterators2_all .................   Passed    0.03 sec
      Start 45: test-json_patch_default
45/78 Test #45: test-json_patch_default .............   Passed    0.02 sec
      Start 46: test-json_patch_all
46/78 Test #46: test-json_patch_all .................   Passed    0.02 sec
      Start 47: test-json_pointer_default
47/78 Test #47: test-json_pointer_default ...........   Passed    0.00 sec
      Start 48: test-json_pointer_all
48/78 Test #48: test-json_pointer_all ...............   Passed    0.00 sec
      Start 49: test-merge_patch_default
49/78 Test #49: test-merge_patch_default ............   Passed    0.00 sec
      Start 50: test-merge_patch_all
50/78 Test #50: test-merge_patch_all ................   Passed    0.00 sec
      Start 51: test-meta_default
51/78 Test #51: test-meta_default ...................   Passed    0.00 sec
      Start 52: test-meta_all
52/78 Test #52: test-meta_all .......................   Passed    0.00 sec
      Start 53: test-modifiers_default
53/78 Test #53: test-modifiers_default ..............   Passed    0.01 sec
      Start 54: test-modifiers_all
54/78 Test #54: test-modifiers_all ..................   Passed    0.01 sec
      Start 55: test-msgpack_default
55/78 Test #55: test-msgpack_default ................   Passed    1.47 sec
      Start 56: test-msgpack_all
56/78 Test #56: test-msgpack_all ....................   Passed   25.01 sec
      Start 57: test-noexcept_default
57/78 Test #57: test-noexcept_default ...............   Passed    0.00 sec
      Start 58: test-noexcept_all
58/78 Test #58: test-noexcept_all ...................   Passed    0.00 sec
      Start 59: test-pointer_access_default
59/78 Test #59: test-pointer_access_default .........   Passed    0.00 sec
      Start 60: test-pointer_access_all
60/78 Test #60: test-pointer_access_all .............   Passed    0.00 sec
      Start 61: test-readme_default
61/78 Test #61: test-readme_default .................   Passed    0.00 sec
      Start 62: test-readme_all
62/78 Test #62: test-readme_all .....................   Passed    0.00 sec
      Start 63: test-reference_access_default
63/78 Test #63: test-reference_access_default .......   Passed    0.00 sec
      Start 64: test-reference_access_all
64/78 Test #64: test-reference_access_all ...........   Passed    0.00 sec
      Start 65: test-regression_default
65/78 Test #65: test-regression_default .............   Passed    4.65 sec
      Start 66: test-regression_all
66/78 Test #66: test-regression_all .................   Passed    4.78 sec
      Start 67: test-serialization_default
67/78 Test #67: test-serialization_default ..........   Passed    0.00 sec
      Start 68: test-serialization_all
68/78 Test #68: test-serialization_all ..............   Passed    0.00 sec
      Start 69: test-testsuites_default
69/78 Test #69: test-testsuites_default .............   Passed    0.10 sec
      Start 70: test-testsuites_all
70/78 Test #70: test-testsuites_all .................   Passed    0.05 sec
      Start 71: test-to_chars_default
71/78 Test #71: test-to_chars_default ...............   Passed    0.00 sec
      Start 72: test-to_chars_all
72/78 Test #72: test-to_chars_all ...................   Passed    0.00 sec
      Start 73: test-ubjson_default
73/78 Test #73: test-ubjson_default .................   Passed    0.80 sec
      Start 74: test-ubjson_all
74/78 Test #74: test-ubjson_all .....................   Passed    9.23 sec
      Start 75: test-udt_default
75/78 Test #75: test-udt_default ....................   Passed    0.00 sec
      Start 76: test-udt_all
76/78 Test #76: test-udt_all ........................   Passed    0.00 sec
      Start 77: test-unicode_default
77/78 Test #77: test-unicode_default ................   Passed    0.01 sec
      Start 78: test-unicode_all
78/78 Test #78: test-unicode_all ....................   Passed  145.24 sec

100% tests passed, 0 tests failed out of 78

Label Time Summary:
all        = 214.25 sec*proc (39 tests)
default    =  13.70 sec*proc (39 tests)

Total Test time (real) = 227.99 sec

[nlohmann]

I think the issue are the braces - there were tickets about the different behaviors between compilers. So

const nlohmann::json j{R"([...])"_json};

may be interpreted as R"([...])"_json with additional braces around which then puts the value into an array.

The code

const nlohmann::json j = R"([...])"_json;

should work fine everywhere.

[nlohmann]

Related #1059.

[nlohmann]

As this issue is a duplicate of #1059 and can also be circumvented by not using braces, I am closing this.