Clang-Tidy warns "undefined or garbage value returned to caller" in any_unique.hpp while using co_await mutex.async_lock()

[Clcanny]

Description

When using co_await on unifex::async_mutex::async_lock() within the provided code, Clang-Tidy produces the warning:

1 warning generated.
../include/unifex/any_unique.hpp:210:5: warning: Undefined or garbage value returned to caller [clang-analyzer-core.uninitialized.UndefReturn]
  210 |     return self.impl_;
      |     ^
/tmp/libunifex/build/test.cc:16:63: note: Calling 'g'
   16 |       unifex::just_from([]() -> unifex::task<void> { co_await g(); }));
      |                                                               ^~~
/tmp/libunifex/build/test.cc:12:12: note: Calling 'f'
   12 |   co_await f();
      |            ^~~
/tmp/libunifex/build/test.cc:8:3: note: Calling 'type::await_transform'
    8 |   co_await mutex.async_lock();
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/task.hpp:373:21: note: 'is_sender_for_v' is false
  373 |       if constexpr (is_sender_for_v<remove_cvref_t<Value>, schedule>) {
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/task.hpp:373:7: note: Taking false branch
  373 |       if constexpr (is_sender_for_v<remove_cvref_t<Value>, schedule>) {
      |       ^
../include/unifex/task.hpp:381:28: note: Assuming the condition is true
  381 |       } else if constexpr (unifex::sender<Value>) {
      |                            ^~~~~~~~~~~~~~~~~~~~~
../include/unifex/task.hpp:381:14: note: Taking true branch
  381 |       } else if constexpr (unifex::sender<Value>) {
      |              ^
../include/unifex/task.hpp:384:13: note: Calling '_fn::operator()'
  384 |             with_scheduler_affinity(static_cast<Value&&>(value), this->sched_));
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/with_scheduler_affinity.hpp:143:9: note: Calling copy constructor for 'any_scheduler'
  143 |         static_cast<Scheduler&&>(sched),
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/any_scheduler.hpp:165:13: note: Calling '_copy_as_fn::operator()'
  165 |     : impl_(_copy_as<any_scheduler>(that.impl_).impl_) {}
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/any_scheduler.hpp:41:12: note: Calling '_fn::operator()'
   41 |     return tag_invoke(*this, t);
      |            ^~~~~~~~~~~~~~~~~~~~
../include/unifex/tag_invoke.hpp:34:12: note: Calling 'tag_invoke'
   34 |     return tag_invoke((CPO &&) cpo, (Args &&) args...);
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/detail/with_type_erased_tag_invoke.hpp:42:22: note: Calling 'get_object_address'
   42 |       void* objPtr = get_object_address(
      |                      ^~~~~~~~~~~~~~~~~~~
   43 |           extract_this<Args...>{}((decltype(args)&&)args...));
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/unifex/any_unique.hpp:210:5: note: Undefined or garbage value returned to caller
  210 |     return self.impl_;
      |     ^      ~~~~~~~~~~

Minimal Reproducible Example

The following code reproduces the issue:

// test.cc
#include <unifex/async_mutex.hpp>
#include <unifex/just_from.hpp>
#include <unifex/sync_wait.hpp>
#include <unifex/task.hpp>
unifex::task<void> f() {
  unifex::async_mutex mutex;
  co_await mutex.async_lock();
  mutex.unlock();
}
unifex::task<void> g() {
  co_await f();
}
int main() {
  unifex::sync_wait(
      unifex::just_from([]() -> unifex::task<void> { co_await g(); }));
  return 0;
}

clang-tidy test.cc -- -std=c++20 -DUNIFEX_NO_ASYNC_STACKS -DUNIFEX_LOG_DANGLING_STOP_CALLBACKS=OFF -I../include

Environment

The issue occurs with the following environment:

root@aa028fac873c:/tmp/libunifex/build# clang++ --version
Debian clang version 19.1.4 (1~deb12u1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-19/bin
root@aa028fac873c:/tmp/libunifex/build# clang-tidy --version
Debian LLVM version 19.1.4
  Optimized build.
root@aa028fac873c:/tmp/libunifex/build# cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"
NAME="Debian GNU/Linux"
VERSION_ID="12"
VERSION="12 (bookworm)"
VERSION_CODENAME=bookworm
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
root@aa028fac873c:/tmp/libunifex/build# git status
HEAD detached at fdd2c23
nothing to commit, working tree clean