[libc++][test] Fix more MSVC and Clang warnings (#74965)

Found while running libc++'s tests with MSVC's STL.

*
`libcxx/test/std/algorithms/alg.sorting/alg.heap.operations/sort.heap/ranges_sort_heap.pass.cpp`
+ Fix Clang `-Wunused-variable`, because `LIBCPP_ASSERT` expands to
nothing for MSVC's STL.
+ This is the same "always void-cast" change that #73437 applied to the
neighboring `complexity.pass.cpp`. I missed that
`ranges_sort_heap.pass.cpp` was also affected because we had disabled
this test.
*
`libcxx/test/std/input.output/file.streams/fstreams/ifstream.members/buffered_reads.pass.cpp`
*
`libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/buffered_writes.pass.cpp`
+ Fix MSVC "warning C4244: '`=`': conversion from '`__int64`' to
'`_Ty`', possible loss of data".
+ This is a valid warning, possibly the best one that MSVC found in this
entire saga. We're accumulating a `std::vector<std::streamsize>` and
storing the result in `std::streamsize total_size` but we actually have
to start with `std::streamsize{0}` or we'll truncate.
*
`libcxx/test/std/input.output/filesystems/fs.enum/enum.path.format.pass.cpp`
+ Fix Clang `-Wunused-local-typedef` because the following usage is
libc++-only.
+ I'm just expanding it at the point of use, and using the dedicated
`LIBCPP_STATIC_ASSERT` to keep the line length down.
*
`libcxx/test/std/input.output/syncstream/syncbuf/syncstream.syncbuf.assign/swap.pass.cpp`
+ Fix MSVC "warning C4242: 'argument': conversion from '`int`' to
'`const _Elem`', possible loss of data".
+ This is a valid warning (possibly the second-best) as `sputc()`
returns `int_type`. If `sputc()` returns something unexpected, we want
to know, so we should separately say `expected.push_back(CharT('B'))`.
*
`libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/new.size_align_nothrow.pass.cpp`
*
`libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/new.size_nothrow.pass.cpp`
  + Fix MSVC "warning C6001: Using uninitialized memory '`x`'."
  + [N4964](https://wg21.link/N4964) \[new.delete.single\]/12:
> *Effects:* The deallocation functions
(\[basic.stc.dynamic.deallocation\]) called by a *delete-expression*
(\[expr.delete\]) to render the value of `ptr` invalid.
  + \[basic.stc.general\]/4:
> When the end of the duration of a region of storage is reached, the
values of all pointers representing the address of any part of that
region of storage become invalid pointer values (\[basic.compound\]).
Indirection through an invalid pointer value and passing an invalid
pointer value to a deallocation function have undefined behavior. Any
other use of an invalid pointer value has implementation-defined
behavior.
+ In certain configurations, after `delete x;` MSVC will consider `x` to
be radioactive (and in other configurations, it'll physically null out
`x` as a safety measure). We can copy it into `old_x` before deletion,
which the implementation finds acceptable.
*
`libcxx/test/std/ranges/range.adaptors/range.elements/general.pass.cpp`
*
`libcxx/test/std/ranges/range.adaptors/range.elements/iterator/deref.pass.cpp`
+ Fix MSVC "warning C4242: 'initializing': conversion from '`_Ty`' to
'`_Ty`', possible loss of data".
+ This was being emitted in `pair` and `tuple`'s perfect forwarding
constructors. Passing `short{1}` allows MSVC to see that no truncation
is happening.
*
`libcxx/test/std/ranges/range.adaptors/range.elements/iterator/member_types.compile.pass.cpp`
+ Fix MSVC "warning C4242: 'initializing': conversion from '`_Ty`' to
'`_Ty2`', possible loss of data".
+ Similarly, this was being emitted in `pair`'s perfect forwarding
constructor. After passing `short{1}`, I reduced repetition by relying
on CTAD. (I can undo that cleanup if it's stylistically undesirable.)
*
`libcxx/test/std/utilities/function.objects/refwrap/refwrap.const/type_conv_ctor.pass.cpp`
+ Fix MSVC "warning C4930: '`std::reference_wrapper<int> purr(void)`':
prototyped function not called (was a variable definition intended?)".
+ There's no reason for `purr()` to be locally declared (aside from
isolating it to a narrow scope, which has minimal benefits); it can be
declared like `meow()` above. 😸
*
`libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.create/make_shared_for_overwrite.pass.cpp`
*
`libcxx/test/std/utilities/smartptr/unique.ptr/unique.ptr.create/make_unique_for_overwrite.default_init.pass.cpp`
  + Fix MSVC static analysis warnings when replacing `operator new`:
    ```
warning C28196: The requirement that '(_Param_(1)>0)?(return!=0):(1)' is
not satisfied. (The expression does not evaluate to true.)
warning C6387: 'return' could be '0': this does not adhere to the
specification for the function 'new'.
warning C6011: Dereferencing NULL pointer 'reinterpret_cast<char
*>ptr+i'.
    ```
+ All we need is a null check, which appears in other `operator new`
replacements:
https://github.com/llvm/llvm-project/blob/b85f1f9b182234ba366d78ae2174a149e44d08c1/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/new.size.replace.pass.cpp#L27-L28

Author: StephanTLavavej

libcxx/test/std/algorithms/alg.sorting/alg.heap.operations/sort.heap/ranges_sort_heap.pass.cpp

@@ -238,6 +238,7 @@ void test_complexity() {
     const int debug_elements = std::min(100, n);
     // Multiplier 2 because of comp(a,b) comp(b, a) checks.
     const int debug_comparisons = 2 * (debug_elements + 1) * debug_elements;
+    (void)debug_comparisons;
     std::shuffle(first, last, g);
     std::make_heap(first, last, &MyInt::Comp);
     // The exact stats of our current implementation are recorded here.
@@ -247,7 +248,6 @@ void test_complexity() {
     LIBCPP_ASSERT(stats.moved <= 2 * n + n * logn);
 #if _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_DEBUG
     LIBCPP_ASSERT(stats.compared <= n * logn);
-    (void)debug_comparisons;
 #else
     LIBCPP_ASSERT(stats.compared <= 2 * n * logn + debug_comparisons);
 #endif

libcxx/test/std/input.output/file.streams/fstreams/ifstream.members/buffered_reads.pass.cpp

@@ -44,7 +44,7 @@
 
 template <class BufferPolicy>
 void test_read(BufferPolicy policy, const std::vector<std::streamsize>& payload_sizes) {
-  std::streamsize total_size = std::accumulate(payload_sizes.begin(), payload_sizes.end(), 0);
+  std::streamsize total_size = std::accumulate(payload_sizes.begin(), payload_sizes.end(), std::streamsize{0});
   std::vector<char> data(total_size);
   for (std::size_t i = 0; i < data.size(); ++i) {
     data[i] = static_cast<char>(i % (1 << 8 * sizeof(char)));
@@ -99,7 +99,7 @@ void test_read(BufferPolicy policy, const std::vector<std::streamsize>& payload_
 #ifndef TEST_HAS_NO_WIDE_CHARACTERS
 template <class BufferPolicy>
 void test_read_codecvt(BufferPolicy policy, const std::vector<std::streamsize>& payload_sizes) {
-  std::streamsize total_size = std::accumulate(payload_sizes.begin(), payload_sizes.end(), 0);
+  std::streamsize total_size = std::accumulate(payload_sizes.begin(), payload_sizes.end(), std::streamsize{0});
   std::vector<wchar_t> data(total_size);
   for (std::size_t i = 0; i < data.size(); ++i) {
     data[i] = static_cast<wchar_t>(i);

libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/buffered_writes.pass.cpp

@@ -45,7 +45,7 @@
 template <class BufferPolicy>
 void test_write(BufferPolicy policy, const std::vector<std::streamsize>& payload_sizes) {
   std::size_t previously_written = 0;
-  std::streamsize total_size     = std::accumulate(payload_sizes.begin(), payload_sizes.end(), 0);
+  std::streamsize total_size     = std::accumulate(payload_sizes.begin(), payload_sizes.end(), std::streamsize{0});
   std::vector<char> data(total_size);
   for (std::size_t i = 0; i < data.size(); ++i) {
     data[i] = static_cast<char>(i % (1 << 8 * sizeof(char)));
@@ -97,7 +97,7 @@ void test_write(BufferPolicy policy, const std::vector<std::streamsize>& payload
 template <class BufferPolicy>
 void test_write_codecvt(BufferPolicy policy, const std::vector<std::streamsize>& payload_sizes) {
   std::size_t previously_written = 0;
-  std::streamsize total_size     = std::accumulate(payload_sizes.begin(), payload_sizes.end(), 0);
+  std::streamsize total_size     = std::accumulate(payload_sizes.begin(), payload_sizes.end(), std::streamsize{0});
   std::vector<wchar_t> data(total_size);
   for (std::size_t i = 0; i < data.size(); ++i) {
     data[i] = static_cast<wchar_t>(i);

libcxx/test/std/input.output/filesystems/fs.enum/enum.path.format.pass.cpp

@@ -25,9 +25,7 @@ int main(int, char**) {
   typedef fs::path::format E;
   static_assert(std::is_enum<E>::value, "");
 
-  typedef std::underlying_type<E>::type UT;
-
-  LIBCPP_ONLY(static_assert(std::is_same<UT, unsigned char>::value, "")); // Implementation detail
+  LIBCPP_STATIC_ASSERT(std::is_same<std::underlying_type<E>::type, unsigned char>::value, ""); // Implementation detail
 
   static_assert(
           E::auto_format   != E::native_format &&

libcxx/test/std/input.output/syncstream/syncbuf/syncstream.syncbuf.assign/swap.pass.cpp

@@ -75,7 +75,8 @@ static void test_short_write_after_swap() {
     sync_buf2.sputn(expected.data(), expected.size());
 
     sync_buf1.swap(sync_buf2);
-    expected.push_back(sync_buf1.sputc(CharT('B')));
+    sync_buf1.sputc(CharT('B'));
+    expected.push_back(CharT('B'));
     sync_buf2.sputc(CharT('Z'));
 
     assert(sstr1.str().empty());

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/new.size.replace.indirect.pass.cpp

@@ -29,7 +29,9 @@ TEST_WORKAROUND_BUG_109234844_WEAK
 void* operator new(std::size_t s) TEST_THROW_SPEC(std::bad_alloc) {
     ++new_called;
     void* ret = std::malloc(s);
-    if (!ret) std::abort(); // placate MSVC's unchecked malloc warning
+    if (!ret) {
+      std::abort(); // placate MSVC's unchecked malloc warning (assert() won't silence it)
+    }
     return  ret;
 }
 

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/new.size.replace.pass.cpp

@@ -27,7 +27,9 @@ int delete_called = 0;
 void* operator new[](std::size_t s) TEST_THROW_SPEC(std::bad_alloc) {
     ++new_called;
     void* ret = std::malloc(s);
-    if (!ret) std::abort(); // placate MSVC's unchecked malloc warning
+    if (!ret) {
+      std::abort(); // placate MSVC's unchecked malloc warning (assert() won't silence it)
+    }
     return  ret;
 }
 

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/new.size_nothrow.replace.indirect.pass.cpp

@@ -33,7 +33,9 @@ TEST_WORKAROUND_BUG_109234844_WEAK
 void* operator new[](std::size_t s) TEST_THROW_SPEC(std::bad_alloc) {
     ++new_called;
     void* ret = std::malloc(s);
-    if (!ret) std::abort(); // placate MSVC's unchecked malloc warning
+    if (!ret) {
+      std::abort(); // placate MSVC's unchecked malloc warning (assert() won't silence it)
+    }
     return ret;
 }
 

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/new.size.replace.pass.cpp

@@ -25,7 +25,9 @@ int delete_called = 0;
 void* operator new(std::size_t s) TEST_THROW_SPEC(std::bad_alloc) {
     ++new_called;
     void* ret = std::malloc(s);
-    if (!ret) std::abort(); // placate MSVC's unchecked malloc warning
+    if (!ret) {
+      std::abort(); // placate MSVC's unchecked malloc warning (assert() won't silence it)
+    }
     return ret;
 }
 

libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/new.size_align_nothrow.pass.cpp

@@ -60,8 +60,9 @@ int main(int, char**) {
         assert(reinterpret_cast<std::uintptr_t>(x) % alignof(TrackLifetimeOverAligned) == 0);
         assert(info.address_constructed == x);
 
+        const auto old_x = x;
         delete x;
-        assert(info.address_destroyed == x);
+        assert(info.address_destroyed == old_x);
     }
 
     return 0;