Fix handling of unexpected arrays in nested described struct fields

[freitass]

Fixes a corner case where, when parsing unexpected arrays in nested JSON objects, the ignoring_handler would incorrectly signal signal_end instead of signal_value, causing the parser to skip the rest of the containing object.

struct X
{
    int a;
    float b;
    std::string c;
};

BOOST_DESCRIBE_STRUCT(X, (), (a, b, c))

struct W
{
    X x;
};

BOOST_DESCRIBE_STRUCT(W, (), (x))

// ...

const auto json = R"(
{
    "x": {
        "unexpected": [],
        "a": 1,
        "b": 3.14,
        "c": "hello"
    }
})";

W w{};
std::error_code ec;
parse_into(w, json, ec);

BOOST_TEST( !ec );               // Ok.
BOOST_TEST( w.x.a == 1 );        // Error: w.x.a is 0
BOOST_TEST( w.x.b == 3.14f );    // Error: w.x.b is 0.0
BOOST_TEST( w.x.c == "hello" );  // Error: w.x.c is ""

[cppalliance-bot]

An automated preview of the documentation is available at https://1129.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2025-12-05 14:22:00 UTC

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1129/pullrequest.html

[grisumbras]

First, thank you for catching and fixing this.

Please, rebase on develop so that CI jobs succeed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.67%. Comparing base (91b6516) to head (707a450).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1129      +/-   ##
===========================================
- Coverage    93.71%   93.67%   -0.05%     
===========================================
  Files           91       91              
  Lines         9153     9153              
===========================================
- Hits          8578     8574       -4     
- Misses         575      579       +4     

Files with missing lines	Coverage Δ
include/boost/json/detail/parse_into.hpp	99.33% <100.00%> (-0.67%)	⬇️

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1129/pullrequest.html

[freitass]

Branch updated, not sure why the coverage dropped -0.05%.

[grisumbras]

Seems like it's a coverage service bug. I'm discussing dropping that. Bad coverage reports are worse than no coverage reports.