clang-tidy: False positive potential memory leak warning with aggregate initialization of unique_ptr members

[faedia]

When using clang-tidy with the clang-analyzer-cplusplus.NewDeleteLeaks check enabled with aggregate initialization of two unique_ptr member variables, a false positive memory leak warning is output.

Reproducer

The code used to reproduce this issue.

#include <memory>

struct Foo {
    std::unique_ptr<int> a;
    std::unique_ptr<int> b;
};

void test_f() {
  Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
}

Steps to reproduce

Run clang tidy with the code above with the clang-analyzer-cplusplus.NewDeleteLeaks check enabled, i.e.:

clang-tidy test.cpp --checks="-*,clang-analyzer-cplusplus.NewDeleteLeaks" -- --std=c++20

Actual output:

1 warning generated.
test.cpp:11:1: warning: Potential leak of memory pointed to by field '_M_head_impl' [clang-analyzer-cplusplus.NewDeleteLeaks]
   11 | }
      | ^
test.cpp:9:14: note: Calling 'make_unique<int, int>'
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
unique_ptr.h:1077:30: note: Memory is allocated
 1077 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:9:14: note: Returned allocated memory
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:11:1: note: Potential leak of memory pointed to by field '_M_head_impl'
   11 | }
      | ^

Expected result

I would expect no warning to be output, since through all possible code paths, the memory owned by the unique_ptr should be deleted.

I have tested this on Ubuntu 25.04:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 25.04
Release:        25.04
Codename:       plucky

With clang-tidy version 20.1.2 installed through apt on my ubuntu system:

$ clang-tidy --version
Ubuntu LLVM version 20.1.2
  Optimized build.

Also see a reproducer on Godbolt: https://godbolt.org/z/GcMqrb3q1

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Emma Tomlinson (faedia)

When using clang-tidy with the `clang-analyzer-cplusplus.NewDeleteLeaks` check enabled with aggregate initialization of two `unique_ptr` member variables, a false positive memory leak warning is output.

Reproducer

The code used to reproduce this issue.

#include <memory>

struct Foo {
    std::unique_ptr<int> a;
    std::unique_ptr<int> b;
};

void test_f() {
  Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
}

Steps to reproduce

Run clang tidy with the code above with the clang-analyzer-cplusplus.NewDeleteLeaks check enabled, i.e.:

clang-tidy test.cpp --checks="-*,clang-analyzer-cplusplus.NewDeleteLeaks" -- --std=c++20

Actual output:

1 warning generated.
test.cpp:11:1: warning: Potential leak of memory pointed to by field '_M_head_impl' [clang-analyzer-cplusplus.NewDeleteLeaks]
   11 | }
      | ^
test.cpp:9:14: note: Calling 'make_unique<int, int>'
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
unique_ptr.h:1077:30: note: Memory is allocated
 1077 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:9:14: note: Returned allocated memory
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:11:1: note: Potential leak of memory pointed to by field '_M_head_impl'
   11 | }
      | ^

Expected result

I would expect no warning to be output, since through all possible code paths, the memory owned by the unique_ptr should be deleted.

I have tested this on Ubuntu 25.05:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 25.04
Release:        25.04
Codename:       plucky

With clang-tidy version 20.1.2 installed through apt on my ubuntu system:

$ clang-tidy --version
Ubuntu LLVM version 20.1.2
  Optimized build.

Also see a reproducer on Godbolt: https://godbolt.org/z/GcMqrb3q1

[llvmbot]

@llvm/issue-subscribers-clang-static-analyzer

Author: Emma Tomlinson (faedia)

When using clang-tidy with the `clang-analyzer-cplusplus.NewDeleteLeaks` check enabled with aggregate initialization of two `unique_ptr` member variables, a false positive memory leak warning is output.

Reproducer

The code used to reproduce this issue.

#include <memory>

struct Foo {
    std::unique_ptr<int> a;
    std::unique_ptr<int> b;
};

void test_f() {
  Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
}

Steps to reproduce

Run clang tidy with the code above with the clang-analyzer-cplusplus.NewDeleteLeaks check enabled, i.e.:

clang-tidy test.cpp --checks="-*,clang-analyzer-cplusplus.NewDeleteLeaks" -- --std=c++20

Actual output:

1 warning generated.
test.cpp:11:1: warning: Potential leak of memory pointed to by field '_M_head_impl' [clang-analyzer-cplusplus.NewDeleteLeaks]
   11 | }
      | ^
test.cpp:9:14: note: Calling 'make_unique<int, int>'
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
unique_ptr.h:1077:30: note: Memory is allocated
 1077 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:9:14: note: Returned allocated memory
    9 |   Foo foo = {std::make_unique<int>(1), std::make_unique<int>(2)};
      |              ^~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:11:1: note: Potential leak of memory pointed to by field '_M_head_impl'
   11 | }
      | ^

Expected result

I would expect no warning to be output, since through all possible code paths, the memory owned by the unique_ptr should be deleted.

I have tested this on Ubuntu 25.04:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 25.04
Release:        25.04
Codename:       plucky

With clang-tidy version 20.1.2 installed through apt on my ubuntu system:

$ clang-tidy --version
Ubuntu LLVM version 20.1.2
  Optimized build.

Also see a reproducer on Godbolt: https://godbolt.org/z/GcMqrb3q1

[vidur2]

Is this claimed? If not I can try to pick it up.

[vidur2]

If no one else is working on this, I’ll go ahead and start on a fix.

[carlosgalvezp]

Sure, go ahead!

@faedia Thanks a lot for the detailed description and minimal reproducer :)

[faedia]

No problem! Another important thing to note for anyone who works on this, another thing I found while doing more test was that allocating the memory for unique_ptr directly inline in the aggregate does not cause the false positive maybe something to do with the temporaries that are returned from the make functions?
The following example does not produce a warning.

void test_f2() {
  Foo foo = {std::unique_ptr<int>(new int(1)), std::unique_ptr<int>(new int(1))};
}

But using some form of maker function (like std::make_unique) does cause the false positive, i.e:

std::unique_ptr<int> my_make_unique(int n)
{
    return std::unique_ptr<int>(new int(n));
}
void test_f3() {
  Foo foo3 = {my_make_unique(1), my_make_unique(2)};
}

Heres a godbolt link for a more comprehensive example: https://godbolt.org/z/ecqrn7qfP

[vidur2]

Is it ok to add explicit handling for this? (ie check if function is returning a unique_ptr in the checker)

[faedia]

I haven't looked into it but I think this issue may be more pervasive for anything similar to unique_ptr, for example shared_ptr and any other user created types that have make functions and take ownership of some memory.

As I say I haven't looked into it, but I could spend some time generalising a reproducer to make it independent of the standard library to demonstrate a base case if you would like?

[vidur2]

If you have time, that'd be great!