No move elision in construction from nested brace-enclosed initializer list

[Fedr]

This program

struct B {
    int i, j;
};

struct A {
    A(A&&) = delete;
    A(const B &) {}
};

A a( { { 1, 2 } } );

is accepted by GCC and EDG. But Clang complains:

<source>:10:3: error: call to deleted constructor of 'A'
   10 | A a( { { 1, 2 } } );
      |   ^  ~~~~~~~~~~~~
<source>:6:5: note: 'A' has been explicitly marked deleted here
    6 |     A(A&&) = delete;
      |     ^

Online demo: https://gcc.godbolt.org/z/eT9M59acx

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Fedor Chelnokov (Fedr)

This program ```c++ struct B { int i, j; };

struct A {
A(A&&) = delete;
A(const B &) {}
};

A a( { { 1, 2 } } );

is accepted by GCC and EDG. But Clang complains:

<source>:10:3: error: call to deleted constructor of 'A'
10 | A a( { { 1, 2 } } );
| ^ ~~~~~~~~~~~~
<source>:6:5: note: 'A' has been explicitly marked deleted here
6 | A(A&&) = delete;
| ^

Online demo: https://gcc.godbolt.org/z/eT9M59acx
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