[clang-tidy] `misc-const-correctness` false positive

[firewave]

#include <memory>
#include <vector>

struct S {};

static void f() {
    /*const*/ S *const newdata = new S;

    std::vector<std::unique_ptr<S>> data;
    data.emplace_back(newdata);
}

<source>:7:15: warning: pointee of variable 'newdata' of type 'S *const' can be declared 'const' [misc-const-correctness]
    7 |     /*const*/ S *const newdata = new S;
      |               ^
      |                  const

https://godbolt.org/z/Yr888PnPn

The resulting code fails to compile:

-checks=-*,misc-const-correctness
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/new_allocator.h:191:23: error: no matching constructor for initialization of 'std::unique_ptr<S>' [clang-diagnostic-error]
  191 |         { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
      |                              ^   ~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/alloc_traits.h:674:8: note: in instantiation of function template specialization 'std::__new_allocator<std::unique_ptr<S>>::construct<std::unique_ptr<S>, const S *const &>' requested here
  674 |           __a.construct(__p, std::forward<_Args>(__args)...);
      |               ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/vector.tcc:121:21: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<std::unique_ptr<S>>>::construct<std::unique_ptr<S>, const S *const &>' requested here
  121 |             _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
      |                            ^
<source>:10:10: note: in instantiation of function template specialization 'std::vector<std::unique_ptr<S>>::emplace_back<const S *const &>' requested here
   10 |     data.emplace_back(newdata);
      |          ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:311:2: note: candidate constructor template not viable: 1st argument ('const S *const') would lose const qualifier
  311 |         unique_ptr(pointer __p) noexcept
      |         ^          ~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:353:12: note: candidate constructor template not viable: no known conversion from 'const S *const' to 'nullptr_t' (aka 'std::nullptr_t') for 1st argument
  353 |         constexpr unique_ptr(nullptr_t) noexcept
      |                   ^          ~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:360:7: note: candidate constructor not viable: no known conversion from 'const S *const' to 'unique_ptr<S>' for 1st argument
  360 |       unique_ptr(unique_ptr&&) = default;
      |       ^          ~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:525:7: note: candidate constructor not viable: no known conversion from 'const S *const' to 'const unique_ptr<S>' for 1st argument
  525 |       unique_ptr(const unique_ptr&) = delete;
      |       ^          ~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:374:2: note: candidate template ignored: could not match 'unique_ptr<_Up, _Ep>' against 'const S *const'
  374 |         unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
      |         ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:385:2: note: candidate template ignored: could not match 'auto_ptr<_Up>' against 'const S *const'
  385 |         unique_ptr(auto_ptr<_Up>&& __u) noexcept;
      |         ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:298:12: note: candidate constructor template not viable: requires 0 arguments, but 1 was provided
  298 |         constexpr unique_ptr() noexcept
      |                   ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:325:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
  325 |         unique_ptr(pointer __p, const deleter_type& __d) noexcept
      |         ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:338:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
  338 |         unique_ptr(pointer __p,
      |         ^          ~~~~~~~~~~~~
  339 |                    __enable_if_t<!is_lvalue_reference<_Del>::value,
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  340 |                                  _Del&&> __d) noexcept
      |                                  ~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:347:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
  347 |         unique_ptr(pointer,
      |         ^          ~~~~~~~~
  348 |                    __enable_if_t<is_lvalue_reference<_Del>::value,
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  349 |                                  _DelUnref&&>) = delete;
      |                                  ~~~~~~~~~~~~

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Oliver Stöneberg (firewave)

```cpp #include <memory> #include <vector>

struct S {};

static void f() {
/const/ S *const newdata = new S;

std::vector<std::unique_ptr<S>> data;
data.emplace_back(newdata);

}

<source>:7:15: warning: pointee of variable 'newdata' of type 'S *const' can be declared 'const' [misc-const-correctness]
7 | /const/ S *const newdata = new S;
| ^
| const

https://godbolt.org/z/Yr888PnPn

The resulting code fails to compile:

-checks=-*,misc-const-correctness
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/new_allocator.h:191:23: error: no matching constructor for initialization of 'std::unique_ptr<S>' [clang-diagnostic-error]
191 | { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/alloc_traits.h:674:8: note: in instantiation of function template specialization 'std::__new_allocator<std::unique_ptr<S>>::construct<std::unique_ptr<S>, const S *const &>' requested here
674 | __a.construct(__p, std::forward<_Args>(__args)...);
| ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/vector.tcc:121:21: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<std::unique_ptr<S>>>::construct<std::unique_ptr<S>, const S *const &>' requested here
121 | _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
| ^
<source>:10:10: note: in instantiation of function template specialization 'std::vector<std::unique_ptr<S>>::emplace_back<const S *const &>' requested here
10 | data.emplace_back(newdata);
| ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:311:2: note: candidate constructor template not viable: 1st argument ('const S *const') would lose const qualifier
311 | unique_ptr(pointer __p) noexcept
| ^ ~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:353:12: note: candidate constructor template not viable: no known conversion from 'const S *const' to 'nullptr_t' (aka 'std::nullptr_t') for 1st argument
353 | constexpr unique_ptr(nullptr_t) noexcept
| ^ ~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:360:7: note: candidate constructor not viable: no known conversion from 'const S *const' to 'unique_ptr<S>' for 1st argument
360 | unique_ptr(unique_ptr&&) = default;
| ^ ~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:525:7: note: candidate constructor not viable: no known conversion from 'const S *const' to 'const unique_ptr<S>' for 1st argument
525 | unique_ptr(const unique_ptr&) = delete;
| ^ ~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:374:2: note: candidate template ignored: could not match 'unique_ptr<_Up, _Ep>' against 'const S *const'
374 | unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
| ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:385:2: note: candidate template ignored: could not match 'auto_ptr<_Up>' against 'const S *const'
385 | unique_ptr(auto_ptr<_Up>&& __u) noexcept;
| ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:298:12: note: candidate constructor template not viable: requires 0 arguments, but 1 was provided
298 | constexpr unique_ptr() noexcept
| ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:325:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
325 | unique_ptr(pointer __p, const deleter_type& __d) noexcept
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:338:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
338 | unique_ptr(pointer __p,
| ^ ~~~~~~~~~~~~
339 | __enable_if_t<!is_lvalue_reference<_Del>::value,
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
340 | _Del&&> __d) noexcept
| ~~~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/bits/unique_ptr.h:347:2: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
347 | unique_ptr(pointer,
| ^ ~~~~~~~~
348 | __enable_if_t<is_lvalue_reference<_Del>::value,
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
349 | _DelUnref&&>) = delete;
| ~~~~~~~~~~~~

</details>

[vbvictor]

We added a new option to analyze pointees so "regression" occurred. You can disable this option, and use the check as in clang-tidy-20

[firewave]

We added a new option to analyze pointees so "regression" occurred. You can disable this option, and use the check as in clang-tidy-20

Thanks for pointing it out. But I only suppressed the single false positive because it found several valid cases as well.