Regression: call to member function 'value' is ambiguous

[sjoubert]

Description

A call to value with a default int value and std::string is now ambiguous in the latest version.

To make it compile I need either to wrap the key value into a std::string_view type or explicitly specify the key template parameter to std::string. None of these spelling are compatible with the previous working version (3.10.5)

Reproduction steps

Minimal code example compiled using C++20 and version 3.11.1
The same code compiles correctly without warning using version 3.10.5

Expected vs. actual results

Results:

• g++-12: warning about ambiguous call, but compilation proceeds
• clang+-14: error about ambiguous call
  Expected: no compilation error on code previously working

Minimal code example

#include <nlohmann/json.hpp>

int main()
{
    nlohmann::json data;
    std::string key = "key";
    data.value(key, 0);
}

Error messages

<source>:7:10: error: call to member function 'value' is ambiguous
    data.value(key, 0);
    ~~~~~^~~~~
/opt/compiler-explorer/libs/nlohmann_json/trunk/single_include/nlohmann/json.hpp:21173:42: note: candidate function [with KeyType = std::basic_string<char>, ValueType = int, $2 = 0]
    typename std::decay<ValueType>::type value(const KeyType& key, ValueType && default_value) const
                                         ^
/opt/compiler-explorer/libs/nlohmann_json/trunk/single_include/nlohmann/json.hpp:21245:14: note: candidate function [with KeyType = std::basic_string<char> &, $1 = 0]
    string_t value(KeyType && key, const char* default_value) const
             ^
1 error generated.

Compiler and operating system

g++-12 (warning) and clang++-14 (error) with -std=c++20

Library version

3.11.1

Validation

• The bug also occurs if the latest version from the develop branch is used.
• I can successfully compile and run the unit tests.

[falbrechtskirchinger]

Confirmed. A bit concerning that this wasn't caught by the unit tests. :-/
Fixing this is going to be a pain …

[dns13]

This also applies for nullptr_t as the default value. But #3663 also fixed this - it's working in dev branch.