Clang does not realize erroneous overload with inherited constructor

[wangbo15]

The following code is rejected by GCC, MSVC, and EDG but accepted by Clang:

struct C
{
    C(int = 1){}
};

struct D
{
  D (C);
};

struct A : D
{
  A (const C & n) : D (C{100}) {}
  using D:: D;
};

int main(){
    A a=C{};
}

As the diagnostic shows, the user-defined ctor A(const C & n) of class A has the same parameter list as the inherited ctor, which leads to ambiguity:

<source>: In function 'int main()':
<source>:18:9: error: conversion from 'C' to 'A' is ambiguous
   18 |     A a=C{};
      |         ^~~
<source>:18:9: note: there are 6 candidates
<source>:8:3: note: candidate 1: 'D::D(C)'
    8 |   D (C);
      |   ^
<source>:14:13: note: inherited here
   14 |   using D:: D;
      |             ^
<source>:13:3: note: candidate 2: 'A::A(const C&)'
   13 |   A (const C & n) : D (C{100}) {}

Please see https://godbolt.org/z/vG9cqvMbc

[llvmbot]

@llvm/issue-subscribers-c-1

Author: Bo Wang (wangbo15)

The following code is rejected by GCC, MSVC, and EDG but accepted by Clang:

struct C
{
    C(int = 1){}
};

struct D
{
  D (C);
};

struct A : D
{
  A (const C & n) : D (C{100}) {}
  using D:: D;
};

int main(){
    A a=C{};
}

As the diagnostic shows, the user-defined ctor A(const C & n) of class A has the same parameter list as the inherited ctor, which leads to ambiguity:

<source>: In function 'int main()':
<source>:18:9: error: conversion from 'C' to 'A' is ambiguous
   18 |     A a=C{};
      |         ^~~
<source>:18:9: note: there are 6 candidates
<source>:8:3: note: candidate 1: 'D::D(C)'
    8 |   D (C);
      |   ^
<source>:14:13: note: inherited here
   14 |   using D:: D;
      |             ^
<source>:13:3: note: candidate 2: 'A::A(const C&)'
   13 |   A (const C & n) : D (C{100}) {}

Please see https://godbolt.org/z/vG9cqvMbc

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Bo Wang (wangbo15)

The following code is rejected by GCC, MSVC, and EDG but accepted by Clang:

struct C
{
    C(int = 1){}
};

struct D
{
  D (C);
};

struct A : D
{
  A (const C & n) : D (C{100}) {}
  using D:: D;
};

int main(){
    A a=C{};
}

As the diagnostic shows, the user-defined ctor A(const C & n) of class A has the same parameter list as the inherited ctor, which leads to ambiguity:

<source>: In function 'int main()':
<source>:18:9: error: conversion from 'C' to 'A' is ambiguous
   18 |     A a=C{};
      |         ^~~
<source>:18:9: note: there are 6 candidates
<source>:8:3: note: candidate 1: 'D::D(C)'
    8 |   D (C);
      |   ^
<source>:14:13: note: inherited here
   14 |   using D:: D;
      |             ^
<source>:13:3: note: candidate 2: 'A::A(const C&)'
   13 |   A (const C & n) : D (C{100}) {}

Please see https://godbolt.org/z/vG9cqvMbc

[zygoloid]

It looks like Clang implements a pre-standard version of [over.match.best.general]/2.7 without the "all parameters have the same type" portion. There's a FIXME for this here.

[Fedr]

It looks similar to #53975

[plopresti]

This is at the root of tensorflow/tensorflow#84977

The code in Tensorflow is erroneous, but Clang accepted it so nobody noticed.