[libc++][format] Don't instantiate direct __(u)int128_t visitation

... in standard `visit_format_arg` and `basic_format_arg::visit`
functions.

There're some internal uses of `__visit_format_arg` where direct
`__(u)int128_t` visitation is valid. This PR doesn't change behavior of
these uses.

Author: frederick-vs-ja

libcxx/include/__format/format_arg.h

@@ -96,11 +96,16 @@ _LIBCPP_HIDE_FROM_ABI constexpr __arg_t __get_packed_type(uint64_t __types, size
   return static_cast<__format::__arg_t>(__types & __packed_arg_t_mask);
 }
 
+enum class __directly_visit_i128 : bool { __no, __yes };
+
 } // namespace __format
 
+template <class _Context>
+class __basic_format_arg_value;
+
 // This function is not user observable, so it can directly use the non-standard
 // types of the "variant". See __arg_t for more details.
-template <class _Visitor, class _Context>
+template <__format::__directly_visit_i128 _DirectlyVisitingI128, class _Visitor, class _Context>
 _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
   switch (__arg.__type_) {
   case __format::__arg_t::__none:
@@ -115,7 +120,12 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
     return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
   case __format::__arg_t::__i128:
 #  if _LIBCPP_HAS_INT128
-    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+    if constexpr (_DirectlyVisitingI128 == __format::__directly_visit_i128::__yes)
+      return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+    else {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
 #  else
     __libcpp_unreachable();
 #  endif
@@ -125,7 +135,12 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
     return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
   case __format::__arg_t::__u128:
 #  if _LIBCPP_HAS_INT128
-    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+    if constexpr (_DirectlyVisitingI128 == __format::__directly_visit_i128::__yes)
+      return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+    else {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
 #  else
     __libcpp_unreachable();
 #  endif
@@ -166,7 +181,10 @@ _LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<
     return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
   case __format::__arg_t::__i128:
 #    if _LIBCPP_HAS_INT128
-    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+  {
+    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+  }
 #    else
     __libcpp_unreachable();
 #    endif
@@ -176,7 +194,10 @@ _LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<
     return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
   case __format::__arg_t::__u128:
 #    if _LIBCPP_HAS_INT128
-    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+  {
+    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+  }
 #    else
     __libcpp_unreachable();
 #    endif
@@ -291,42 +312,14 @@ class _LIBCPP_NO_SPECIALIZATIONS basic_format_arg {
   // the "variant" in a handle to stay conforming. See __arg_t for more details.
   template <class _Visitor>
   _LIBCPP_HIDE_FROM_ABI decltype(auto) visit(this basic_format_arg __arg, _Visitor&& __vis) {
-    switch (__arg.__type_) {
-#    if _LIBCPP_HAS_INT128
-    case __format::__arg_t::__i128: {
-      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
-      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-    }
-
-    case __format::__arg_t::__u128: {
-      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
-      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-    }
-#    endif
-    default:
-      return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
-    }
+    return std::__visit_format_arg<__format::__directly_visit_i128::__no>(std::forward<_Visitor>(__vis), __arg);
   }
 
   // This function is user facing, so it must wrap the non-standard types of
   // the "variant" in a handle to stay conforming. See __arg_t for more details.
   template <class _Rp, class _Visitor>
   _LIBCPP_HIDE_FROM_ABI _Rp visit(this basic_format_arg __arg, _Visitor&& __vis) {
-    switch (__arg.__type_) {
-#    if _LIBCPP_HAS_INT128
-    case __format::__arg_t::__i128: {
-      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
-      return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-    }
-
-    case __format::__arg_t::__u128: {
-      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
-      return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-    }
-#    endif
-    default:
-      return std::__visit_format_arg<_Rp>(std::forward<_Visitor>(__vis), __arg);
-    }
+    return std::__visit_format_arg<_Rp>(std::forward<_Visitor>(__vis), __arg);
   }
 
 #  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
@@ -376,21 +369,7 @@ _LIBCPP_DEPRECATED_IN_CXX26
 #  endif
     _LIBCPP_HIDE_FROM_ABI decltype(auto)
     visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
-  switch (__arg.__type_) {
-#  if _LIBCPP_HAS_INT128
-  case __format::__arg_t::__i128: {
-    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
-    return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-  }
-
-  case __format::__arg_t::__u128: {
-    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
-    return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
-  }
-#  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
-  default:
-    return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
-  }
+  return std::__visit_format_arg<__format::__directly_visit_i128::__no>(std::forward<_Visitor>(__vis), __arg);
 }
 
 #endif // _LIBCPP_STD_VER >= 20

libcxx/include/__format/format_functions.h

@@ -272,7 +272,7 @@ __handle_replacement_field(_Iterator __begin, _Iterator __end, _ParseCtx& __pars
     else if (__parse)
       __format::__compile_time_visit_format_arg(__parse_ctx, __ctx, __type);
   } else
-    std::__visit_format_arg(
+    std::__visit_format_arg<__format::__directly_visit_i128::__yes>(
         [&](auto __arg) {
           if constexpr (same_as<decltype(__arg), monostate>)
             std::__throw_format_error("The argument index value is too large for the number of arguments supplied");

libcxx/include/__format/parser_std_format_spec.h

@@ -91,7 +91,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr uint32_t __substitute_arg_id(basic_format_arg<_C
   // This means the 128-bit will not be valid anymore.
   // TODO FMT Verify this resolution is accepted and add a test to verify
   //          128-bit integrals fail and switch to visit_format_arg.
-  return std::__visit_format_arg(
+  return std::__visit_format_arg<__format::__directly_visit_i128::__yes>(
       [](auto __arg) -> uint32_t {
         using _Type = decltype(__arg);
         if constexpr (same_as<_Type, monostate>)

libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp

@@ -28,6 +28,28 @@
 #include "min_allocator.h"
 #include "test_macros.h"
 
+template <class Context>
+struct limited_visitor {
+  using CharT = Context::char_type;
+
+  void operator()(std::monostate) const {}
+  void operator()(bool) const {}
+  void operator()(CharT) const {}
+  void operator()(int) const {}
+  void operator()(unsigned int) const {}
+  void operator()(long long) const {}
+  void operator()(unsigned long long) const {}
+  void operator()(float) const {}
+  void operator()(double) const {}
+  void operator()(long double) const {}
+  void operator()(const CharT*) const {}
+  void operator()(std::basic_string_view<CharT>) const {}
+  void operator()(const void*) const {}
+  void operator()(const std::basic_format_arg<Context>::handle&) const {}
+
+  void operator()(auto) const = delete;
+};
+
 template <class Context, class To, class From>
 void test(From value) {
   auto store = std::make_format_args<Context>(value);
@@ -36,6 +58,9 @@ void test(From value) {
   LIBCPP_ASSERT(format_args.__size() == 1);
   assert(format_args.get(0));
 
+  // https://github.com/llvm/llvm-project/issues/139582
+  format_args.get(0).visit(limited_visitor<Context>{});
+
   auto result = format_args.get(0).visit([v = To(value)](auto a) -> To {
     if constexpr (std::is_same_v<To, decltype(a)>) {
       assert(v == a);
@@ -60,6 +85,9 @@ void test_handle(T value) {
   LIBCPP_ASSERT(format_args.__size() == 1);
   assert(format_args.get(0));
 
+  // https://github.com/llvm/llvm-project/issues/139582
+  format_args.get(0).visit(limited_visitor<Context>{});
+
   format_args.get(0).visit([](auto a) {
     assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>));
   });

libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp

@@ -117,6 +117,48 @@ void test_string_view(From value, ExpectedR expectedValue) {
   assert(result == expectedValue);
 }
 
+template <class Context>
+struct limited_int_visitor {
+  using CharT = Context::char_type;
+
+  int operator()(std::monostate) const { return 1; }
+  int operator()(bool) const { return 2; }
+  int operator()(CharT) const { return 3; }
+  int operator()(int) const { return 4; }
+  int operator()(unsigned int) const { return 5; }
+  int operator()(long long) const { return 6; }
+  int operator()(unsigned long long) const { return 7; }
+  int operator()(float) const { return 8; }
+  int operator()(double) const { return 9; }
+  int operator()(long double) const { return 10; }
+  int operator()(const CharT*) const { return 11; }
+  int operator()(std::basic_string_view<CharT>) const { return 12; }
+  int operator()(const void*) const { return 13; }
+  int operator()(const std::basic_format_arg<Context>::handle&) const { return 14; }
+
+  void operator()(auto) const = delete;
+};
+
+// https://github.com/llvm/llvm-project/issues/139582
+template <class Context, class ExpectedR, class From>
+void test_limited_visitation(From value) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  if constexpr (std::is_void_v<ExpectedR>) {
+    format_args.get(0).template visit<ExpectedR>(limited_int_visitor<Context>{});
+    static_assert(
+        std::is_same_v<void, decltype(format_args.get(0).template visit<ExpectedR>(limited_int_visitor<Context>{}))>);
+  } else {
+    std::same_as<ExpectedR> decltype(auto) result =
+        format_args.get(0).template visit<ExpectedR>(limited_int_visitor<Context>{});
+    assert(result);
+  }
+}
+
 template <class CharT>
 void test() {
   using Context = std::basic_format_context<CharT*, CharT>;
@@ -354,6 +396,25 @@ void test() {
   test<Context, const void*, ExpectedResultType>(static_cast<void*>(&i), visited);
   const int ci = 0;
   test<Context, const void*, ExpectedResultType>(static_cast<const void*>(&ci), visited);
+
+  // https://github.com/llvm/llvm-project/issues/139582
+  // Test limited visitors.
+  test_limited_visitation<Context, void>(true);
+  test_limited_visitation<Context, void>(42);
+  test_limited_visitation<Context, void>(0.5);
+  test_limited_visitation<Context, void>(str);
+#ifndef TEST_HAS_NO_INT128
+  test_limited_visitation<Context, void>(__int128_t{0});
+  test_limited_visitation<Context, void>(__uint128_t{0});
+#endif // TEST_HAS_NO_INT128
+  test_limited_visitation<Context, long>(true);
+  test_limited_visitation<Context, long>(42);
+  test_limited_visitation<Context, long>(0.5);
+  test_limited_visitation<Context, long>(str);
+#ifndef TEST_HAS_NO_INT128
+  test_limited_visitation<Context, long>(__int128_t{0});
+  test_limited_visitation<Context, long>(__uint128_t{0});
+#endif // TEST_HAS_NO_INT128
 }
 
 int main(int, char**) {

libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp

@@ -19,6 +19,7 @@
 #include <cassert>
 #include <limits>
 #include <type_traits>
+#include <variant>
 
 #include "constexpr_char_traits.h"
 #include "test_macros.h"
@@ -29,6 +30,28 @@
 TEST_CLANG_DIAGNOSTIC_IGNORED("-Wdeprecated-declarations")
 #endif
 
+template <class Context>
+struct limited_visitor {
+  using CharT = Context::char_type;
+
+  void operator()(std::monostate) const {}
+  void operator()(bool) const {}
+  void operator()(CharT) const {}
+  void operator()(int) const {}
+  void operator()(unsigned int) const {}
+  void operator()(long long) const {}
+  void operator()(unsigned long long) const {}
+  void operator()(float) const {}
+  void operator()(double) const {}
+  void operator()(long double) const {}
+  void operator()(const CharT*) const {}
+  void operator()(std::basic_string_view<CharT>) const {}
+  void operator()(const void*) const {}
+  void operator()(const std::basic_format_arg<Context>::handle&) const {}
+
+  void operator()(auto) const = delete;
+};
+
 template <class Context, class To, class From>
 void test(From value) {
   auto store = std::make_format_args<Context>(value);
@@ -37,6 +60,9 @@ void test(From value) {
   LIBCPP_ASSERT(format_args.__size() == 1);
   assert(format_args.get(0));
 
+  // https://github.com/llvm/llvm-project/issues/139582
+  std::visit_format_arg(limited_visitor<Context>{}, format_args.get(0));
+
   auto result = std::visit_format_arg(
       [v = To(value)](auto a) -> To {
         if constexpr (std::is_same_v<To, decltype(a)>) {
@@ -63,6 +89,9 @@ void test_handle(T value) {
   LIBCPP_ASSERT(format_args.__size() == 1);
   assert(format_args.get(0));
 
+  // https://github.com/llvm/llvm-project/issues/139582
+  std::visit_format_arg(limited_visitor<Context>{}, format_args.get(0));
+
   std::visit_format_arg(
       [](auto a) { assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>)); },
       format_args.get(0));