In copy-list-initialization, if an explicit constructor is chosen, the initialization is ill-formed and the diagnostic should be reported.

[romanova-ekaterina]

Consider the following testcase (see below).

According to 13.3.1.7 Initialization by list-initialization is C++11 standard
"In copy-list-initialization, if an explicit constructor is chosen, the initialization is ill-formed."
However, clang doesn't report an error.

#include <initializer_list>
class AAA {
public:
    AAA(int,int,int) {
    }
};

class BBB {
    int value;
public:
    BBB() : value(10) {
    }

    BBB(const AAA& ) : value(20) {
    }

    explicit BBB(int,int,int) : value(33) {
    }

    int get_value()  {
	return value;
    }
};

int test_function (void) {
    BBB b({10,13,17}); // Diagnostic message should be reported here?
    return 1;
}

int main() { 
    test_function();
}

Clang doesn't report any diagnostic for it.

Microsoft's cl compiler (version 19) complains about it:

cl /c test.cpp /all
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30154 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

cl : Command line warning D9002 : ignoring unknown option '/all'
test.cpp
test.cpp(26): error C2664: 'BBB::BBB(BBB &&)': cannot convert argument 1 from 'initializer list' to 'BBB &&'
test.cpp(26): note: copy-list-initialization of 'BBB' cannot use an explicit constructor
test.cpp(17): note: see declaration of 'BBB::BBB'

Older gcc compiler (gcc 10.2.0) also complains about it:

$ gcc -c test.cpp -Wall
test.cpp: In function ‘int test_function()’:
test.cpp:26:21: error: call of overloaded ‘BBB(<brace-enclosed initializer list>)’ is ambiguous
   26 |     BBB b({10,13,17}); // Diagnostic message should be reported here?
      |                     ^
test.cpp:14:5: note: candidate: ‘BBB::BBB(const AAA&)’
   14 |     BBB(const AAA& ) : value(20) {
      |     ^~~
test.cpp:8:7: note: candidate: ‘constexpr BBB::BBB(const BBB&)’
    8 | class BBB {
      |       ^~~
test.cpp:8:7: note: candidate: ‘constexpr BBB::BBB(BBB&&)’
test.cpp:26:9: warning: unused variable ‘b’ [-Wunused-variable]
   26 |     BBB b({10,13,17}); // Diagnostic message should be reported here?
      |         ^