[deque] fix: copy_construct_impl source pointer, emplace_decision::po…

[SekaiArendelle]

…s type, null-pointer guard in deque(n,val)

• copy_construct_impl for non-trivial types: use fromcontroller.front_block.curr_ptr instead of controller.front_block.curr_ptr for single-block case
• emplace_decision::pos changed from ::std::size_t to iterator type
• deque(size_type, const_reference) add early return for n==0 to avoid null-pointer arithmetic in set_newed_common

Add tests: access, algorithm, assign_range, capacity, compare, concepts, constructors/iter_iter, constructors/n_val, insert_initializer_list, insert_range_iterator, invalidation, move_only, self_reference, swap, type_traits

[SekaiArendelle]

// Bug 1: copy_construct_impl uses destination's front_block.curr_ptr
// instead of source's (fromcontroller.front_block.curr_ptr) for the
// single-block non-trivial copy path.
//
// Without fix: copy-constructing a deque of non-trivial elements
// that fit in one block reads from uninitialized destination memory.
//
// Fix: deque.h:2231  lastblockbegin = fromcontroller.front_block.curr_ptr

#include <fast_io.h>
#include <fast_io_dsal/deque.h>
#include <fast_io_dsal/string.h>

int main()
{
        ::fast_io::deque<::fast_io::string> dq;
        for (::std::size_t i{}; i != 50u; ++i)
        {
                dq.emplace_back(::fast_io::concat_fast_io("hello_", i));
        }

        ::fast_io::deque<::fast_io::string> copy = dq;

        for (::std::size_t i{}; i != 50u; ++i)
        {
                if (copy[i] != dq[i])
                {
                        ::fast_io::io::panicln("Bug 1 reproduced: copy[", i, "] != dq[", i, "]");
                }
        }
        ::fast_io::io::print("Bug 1 NOT reproduced (copy matches source)\n");
}

[SekaiArendelle]

// Bug 2: deque(size_type n, const_reference val) constructor has no
// early return for n==0, and controller is not zero-initialized.
// This causes UB in set_newed_common via begin() on garbage controller.
//
// Without fix: constructing deque(0, val) invokes UB (uninitialized
// controller members).  Under constexpr evaluation this is a hard error.
// With ASan/UBSan this is caught at runtime.
//
// Fix: deque.h:2344  add ": controller{}" and "if (!n) return;"

#include <fast_io.h>
#include <fast_io_dsal/deque.h>

constexpr bool test()
{
        ::fast_io::deque<int> dq(0, 42);
        return dq.empty();
}
static_assert(test());

int main()
{
        ::fast_io::deque<int> dq(0, 42);
        if (!dq.empty())
        {
                ::fast_io::io::panic("Bug 2 reproduced: deque(0, val) is not empty\n");
        }
        ::fast_io::io::print("Bug 2 NOT reproduced (deque(0, val) is empty)\n");
}

> clang++ repro/bug2_deque_zero_n_val.cc -o build\test.exe -std=c++23 -I include\ -lntdll
repro/bug2_deque_zero_n_val.cc:19:15: error: static assertion expression is not an integral constant expression
   19 | static_assert(test());
      |               ^~~~~~
include/fast_io_dsal/impl/deque.h:1944:58: note: read of uninitialized object is not allowed in a constant expression
 1944 |         ::std::size_t controllerdiff{static_cast<::std::size_t>(a.controller_ptr - b.controller_ptr)};
      |                                                                 ^~~~~~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:1959:11: note: in call to 'deque_itercontent_diff_impl<fast_io::containers::details::deque_control_block<int>>(dq.controller.back_block, dq.controller.front_block, 1024)'
 1959 |                 deqsz = ::fast_io::containers::details::deque_itercontent_diff_impl(controller.back_block, controller.front_block, block_size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:1993:2: note: in call to 'deque_reserve_back_impl<fast_io::generic_allocator_adapter<fast_io::nt_rtlallocateheap_allocator>, false,
      fast_io::containers::details::deque_controller<int>>(dq.controller, 0, 4, 4, 1024)'
 1993 |         ::fast_io::containers::details::deque_reserve_back_impl<allocator, divsz>(controller, newbackcap, align, sz, block_size);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:3605:4: note: in call to 'deque_reserve_back_common<fast_io::generic_allocator_adapter<fast_io::nt_rtlallocateheap_allocator>, 4ULL, 4ULL, 1024ULL, false,
      fast_io::containers::details::deque_controller<int>>(dq.controller, 0)'
 3605 |                         ::fast_io::containers::details::deque_reserve_back_common<allocator, alignof(value_type), sizeof(value_type), block_size, false>(this->controller, backcap);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:2348:4: note: in call to 'this->reserve_back(0)'
 2348 |                         this->reserve_back(n);
      |                         ^~~~~~~~~~~~~~~~~~~~~
repro/bug2_deque_zero_n_val.cc:16:24: note: in call to 'deque(0, 42)'
   16 |         ::fast_io::deque<int> dq(0, 42);
      |                               ^~~~~~~~~
repro/bug2_deque_zero_n_val.cc:19:15: note: in call to 'test()'
   19 | static_assert(test());
      |               ^~~~~~
1 error generated.

[SekaiArendelle]

// Bug 3: emplace_decision::pos is ::std::size_t instead of iterator.
// The structured binding in emplace() for the non-nothrow path
// (auto [retit, decision] = emplace_decision_common<false>(iter))
// expects retit to be an iterator, but gets size_t instead.
//
// deque_iterator has no conversion to size_t, so the aggregate
// initialization emplace_decision{retit, ...} fails to compile
// for non-nothrow-constructible types.
//
// Fix: deque.h:3308  ::std::size_t pos → iterator pos

#include <fast_io.h>
#include <fast_io_dsal/deque.h>

struct NonNoThrow
{
        int value;
        NonNoThrow(int v) : value(v) {}
};

int main()
{
        ::fast_io::deque<NonNoThrow> dq;
        dq.push_back(NonNoThrow(1));
        dq.push_back(NonNoThrow(2));

        auto it = dq.emplace(dq.begin(), 42);

        if (it->value != 42 || dq.size() != 3u)
        {
                ::fast_io::io::panic("Bug 3 reproduced: emplace result is wrong\n");
        }
        ::fast_io::io::print("Bug 3 NOT reproduced (emplace works)\n");
}

> clang++ repro/bug3_emplace_non_nothrow.cc -o build\test.exe -std=c++23 -I include\ -lntdll
In file included from repro/bug3_emplace_non_nothrow.cc:13:
In file included from include/fast_io_dsal/deque.h:28:
include/fast_io_dsal/impl/deque.h:3330:30: error: no viable conversion from 'iterator' (aka '::fast_io::containers::details::deque_iterator<NonNoThrow, false>') to '::std::size_t' (aka 'unsigned long long')
 3330 |                                         return emplace_decision{retit, 1};
      |                                                                 ^~~~~
include/fast_io_dsal/impl/deque.h:3490:35: note: in instantiation of function template specialization 'fast_io::containers::deque<NonNoThrow,
      fast_io::generic_allocator_adapter<fast_io::nt_rtlallocateheap_allocator>>::emplace_decision_common<false>' requested here
 3490 |                         auto [retit, decision] = this->emplace_decision_common<false>(iter);
      |                                                        ^
repro/bug3_emplace_non_nothrow.cc:27:15: note: in instantiation of function template specialization 'fast_io::containers::deque<NonNoThrow,
      fast_io::generic_allocator_adapter<fast_io::nt_rtlallocateheap_allocator>>::emplace<int>' requested here
   27 |         auto it = dq.emplace(dq.begin(), 42);
      |                      ^
include/fast_io_dsal/impl/deque.h:338:19: note: candidate function
  338 |         inline constexpr operator deque_iterator<T, true>() const noexcept
      |                          ^
include/fast_io_dsal/impl/deque.h:3358:28: error: no viable conversion from 'iterator' (aka '::fast_io::containers::details::deque_iterator<NonNoThrow, false>') to '::std::size_t' (aka 'unsigned long long')
 3358 |                         return emplace_decision{retit, 0};
      |                                                 ^~~~~
include/fast_io_dsal/impl/deque.h:338:19: note: candidate function
  338 |         inline constexpr operator deque_iterator<T, true>() const noexcept
      |                          ^
include/fast_io_dsal/impl/deque.h:3491:30: error: cannot initialize a member subobject of type 'NonNoThrow *' with an lvalue of type '::std::size_t' (aka 'unsigned long long')
 3491 |                         emplace_guard guard{this, retit, decision};
      |                                                   ^~~~~
repro/bug3_emplace_non_nothrow.cc:27:15: note: in instantiation of function template specialization 'fast_io::containers::deque<NonNoThrow,
      fast_io::generic_allocator_adapter<fast_io::nt_rtlallocateheap_allocator>>::emplace<int>' requested here
   27 |         auto it = dq.emplace(dq.begin(), 42);
      |                      ^
In file included from repro/bug3_emplace_non_nothrow.cc:13:
In file included from include/fast_io_dsal/deque.h:28:
include/fast_io_dsal/impl/deque.h:3491:37: error: cannot initialize a member subobject of type 'NonNoThrow *' with an lvalue of type '::std::int_fast8_t' (aka 'signed char')
 3491 |                         emplace_guard guard{this, retit, decision};
      |                                                          ^~~~~~~~
include/fast_io_dsal/impl/deque.h:3492:29: error: member reference base type '::std::size_t' (aka 'unsigned long long') is not a structure or union
 3492 |                         ::std::construct_at(retit.itercontent.curr_ptr, ::std::forward<Args>(args)...);
      |                                             ~~~~~^~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:3494:11: error: no viable conversion from returned value of type '::std::size_t' (aka 'unsigned long long') to function return type 'iterator' (aka
      '::fast_io::containers::details::deque_iterator<NonNoThrow, false>')
 3494 |                         return retit;
      |                                ^~~~~
include/fast_io_dsal/impl/deque.h:237:8: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from '::std::size_t' (aka 'unsigned long long') to
      'const deque_iterator<NonNoThrow, false> &' for 1st argument
  237 | struct deque_iterator
      |        ^~~~~~~~~~~~~~
include/fast_io_dsal/impl/deque.h:237:8: note: candidate constructor (the implicit move constructor) not viable: no known conversion from '::std::size_t' (aka 'unsigned long long') to
      'deque_iterator<NonNoThrow, false> &&' for 1st argument
  237 | struct deque_iterator
      |        ^~~~~~~~~~~~~~
6 errors generated.