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

libcxx/include/__format/format_arg.h

@@ -56,7 +56,7 @@ namespace __format {
 /// @note Some members of this enum are an extension. These extensions need
 /// special behaviour in visit_format_arg. There they need to be wrapped in a
 /// handle to satisfy the user observable behaviour. The internal function
-/// __visit_format_arg doesn't do this wrapping. So in the format functions
+/// __directly_visit_format_arg doesn't do this wrapping. So in the format functions
 /// this function is used to avoid unneeded overhead.
 enum class __arg_t : uint8_t {
   __none,
@@ -98,10 +98,86 @@ _LIBCPP_HIDE_FROM_ABI constexpr __arg_t __get_packed_type(uint64_t __types, size
 
 } // namespace __format
 
-// This function is not user observable, so it can directly use the non-standard
-// types of the "variant". See __arg_t for more details.
+/// Contains the values used in basic_format_arg.
+///
+/// This is a separate type so it's possible to store the values and types in
+/// separate arrays.
+template <class _Context>
+class __basic_format_arg_value {
+  using _CharT _LIBCPP_NODEBUG = typename _Context::char_type;
+
+public:
+  /// Contains the implementation for basic_format_arg::handle.
+  struct __handle {
+    template <class _Tp>
+    _LIBCPP_HIDE_FROM_ABI explicit __handle(_Tp& __v) noexcept
+        : __ptr_(std::addressof(__v)),
+          __format_([](basic_format_parse_context<_CharT>& __parse_ctx, _Context& __ctx, const void* __ptr) {
+            using _Dp = remove_const_t<_Tp>;
+            using _Qp = conditional_t<__formattable_with<const _Dp, _Context>, const _Dp, _Dp>;
+            static_assert(__formattable_with<_Qp, _Context>, "Mandated by [format.arg]/10");
+
+            typename _Context::template formatter_type<_Dp> __f;
+            __parse_ctx.advance_to(__f.parse(__parse_ctx));
+            __ctx.advance_to(__f.format(*const_cast<_Qp*>(static_cast<const _Dp*>(__ptr)), __ctx));
+          }) {}
+
+    const void* __ptr_;
+    void (*__format_)(basic_format_parse_context<_CharT>&, _Context&, const void*);
+  };
+
+  union {
+    monostate __monostate_;
+    bool __boolean_;
+    _CharT __char_type_;
+    int __int_;
+    unsigned __unsigned_;
+    long long __long_long_;
+    unsigned long long __unsigned_long_long_;
+#  if _LIBCPP_HAS_INT128
+    __int128_t __i128_;
+    __uint128_t __u128_;
+#  endif
+    float __float_;
+    double __double_;
+    long double __long_double_;
+    const _CharT* __const_char_type_ptr_;
+    basic_string_view<_CharT> __string_view_;
+    const void* __ptr_;
+    __handle __handle_;
+  };
+
+  // These constructors contain the exact storage type used. If adjustments are
+  // required, these will be done in __create_format_arg.
+
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value() noexcept : __monostate_() {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(bool __value) noexcept : __boolean_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(_CharT __value) noexcept : __char_type_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(int __value) noexcept : __int_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned __value) noexcept : __unsigned_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long long __value) noexcept : __long_long_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned long long __value) noexcept
+      : __unsigned_long_long_(__value) {}
+#  if _LIBCPP_HAS_INT128
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__int128_t __value) noexcept : __i128_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__uint128_t __value) noexcept : __u128_(__value) {}
+#  endif
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(float __value) noexcept : __float_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(double __value) noexcept : __double_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long double __value) noexcept : __long_double_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const _CharT* __value) noexcept : __const_char_type_ptr_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(basic_string_view<_CharT> __value) noexcept
+      : __string_view_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const void* __value) noexcept : __ptr_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__handle&& __value) noexcept : __handle_(std::move(__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. For direct visitation, see https://reviews.llvm.org/D138052.
+// TODO: Investigate why GCC 15 hangs if something like std::__visit_format_arg<__direct::__yes>(...) is used, and fuse
+// __visit_format_arg and __directly_visit_format_arg once GCC no longer hangs.
 template <class _Visitor, class _Context>
-_LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+_LIBCPP_HIDE_FROM_ABI decltype(auto) __directly_visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
   switch (__arg.__type_) {
   case __format::__arg_t::__none:
     return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__monostate_);
@@ -149,6 +225,64 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
   __libcpp_unreachable();
 }
 
+// __visit_format_arg is same as __directly_visit_format_arg except for indirectly visitation of 128-bit integers.
+// Per [format.arg], the variant alternative types are fully specified, so we need to avoid direct visitation of 128-bit
+// extended integer types when the visitor is user-provided.
+template <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:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__monostate_);
+  case __format::__arg_t::__boolean:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__boolean_);
+  case __format::__arg_t::__char_type:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__char_type_);
+  case __format::__arg_t::__int:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__int_);
+  case __format::__arg_t::__long_long:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
+  case __format::__arg_t::__i128:
+#  if _LIBCPP_HAS_INT128
+  {
+    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
+  case __format::__arg_t::__unsigned:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_);
+  case __format::__arg_t::__unsigned_long_long:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
+  case __format::__arg_t::__u128:
+#  if _LIBCPP_HAS_INT128
+  {
+    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
+  case __format::__arg_t::__float:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__float_);
+  case __format::__arg_t::__double:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__double_);
+  case __format::__arg_t::__long_double:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__long_double_);
+  case __format::__arg_t::__const_char_type_ptr:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__const_char_type_ptr_);
+  case __format::__arg_t::__string_view:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__string_view_);
+  case __format::__arg_t::__ptr:
+    return std::invoke(std::forward<_Visitor>(__vis), __arg.__value_.__ptr_);
+  case __format::__arg_t::__handle:
+    return std::invoke(
+        std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__arg.__value_.__handle_});
+  }
+
+  __libcpp_unreachable();
+}
+
 #  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
 
 template <class _Rp, class _Visitor, class _Context>
@@ -166,7 +300,10 @@ _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_.__i128_};
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+  }
 #    else
     __libcpp_unreachable();
 #    endif
@@ -176,7 +313,10 @@ _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
@@ -202,80 +342,6 @@ _LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<
 
 #  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
 
-/// Contains the values used in basic_format_arg.
-///
-/// This is a separate type so it's possible to store the values and types in
-/// separate arrays.
-template <class _Context>
-class __basic_format_arg_value {
-  using _CharT _LIBCPP_NODEBUG = typename _Context::char_type;
-
-public:
-  /// Contains the implementation for basic_format_arg::handle.
-  struct __handle {
-    template <class _Tp>
-    _LIBCPP_HIDE_FROM_ABI explicit __handle(_Tp& __v) noexcept
-        : __ptr_(std::addressof(__v)),
-          __format_([](basic_format_parse_context<_CharT>& __parse_ctx, _Context& __ctx, const void* __ptr) {
-            using _Dp = remove_const_t<_Tp>;
-            using _Qp = conditional_t<__formattable_with<const _Dp, _Context>, const _Dp, _Dp>;
-            static_assert(__formattable_with<_Qp, _Context>, "Mandated by [format.arg]/10");
-
-            typename _Context::template formatter_type<_Dp> __f;
-            __parse_ctx.advance_to(__f.parse(__parse_ctx));
-            __ctx.advance_to(__f.format(*const_cast<_Qp*>(static_cast<const _Dp*>(__ptr)), __ctx));
-          }) {}
-
-    const void* __ptr_;
-    void (*__format_)(basic_format_parse_context<_CharT>&, _Context&, const void*);
-  };
-
-  union {
-    monostate __monostate_;
-    bool __boolean_;
-    _CharT __char_type_;
-    int __int_;
-    unsigned __unsigned_;
-    long long __long_long_;
-    unsigned long long __unsigned_long_long_;
-#  if _LIBCPP_HAS_INT128
-    __int128_t __i128_;
-    __uint128_t __u128_;
-#  endif
-    float __float_;
-    double __double_;
-    long double __long_double_;
-    const _CharT* __const_char_type_ptr_;
-    basic_string_view<_CharT> __string_view_;
-    const void* __ptr_;
-    __handle __handle_;
-  };
-
-  // These constructors contain the exact storage type used. If adjustments are
-  // required, these will be done in __create_format_arg.
-
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value() noexcept : __monostate_() {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(bool __value) noexcept : __boolean_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(_CharT __value) noexcept : __char_type_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(int __value) noexcept : __int_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned __value) noexcept : __unsigned_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long long __value) noexcept : __long_long_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned long long __value) noexcept
-      : __unsigned_long_long_(__value) {}
-#  if _LIBCPP_HAS_INT128
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__int128_t __value) noexcept : __i128_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__uint128_t __value) noexcept : __u128_(__value) {}
-#  endif
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(float __value) noexcept : __float_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(double __value) noexcept : __double_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long double __value) noexcept : __long_double_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const _CharT* __value) noexcept : __const_char_type_ptr_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(basic_string_view<_CharT> __value) noexcept
-      : __string_view_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const void* __value) noexcept : __ptr_(__value) {}
-  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__handle&& __value) noexcept : __handle_(std::move(__value)) {}
-};
-
 template <class _Context>
 class _LIBCPP_NO_SPECIALIZATIONS basic_format_arg {
 public:
@@ -291,42 +357,14 @@ 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(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 +414,7 @@ _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(std::forward<_Visitor>(__vis), __arg);
 }
 
 #endif // _LIBCPP_STD_VER >= 20

libcxx/include/__format/format_functions.h

@@ -275,7 +275,7 @@ __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( // TODO: Use __directly_visit_format_arg?
         [&](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");
@@ -468,7 +468,7 @@ template <class _CharT>
   if (auto __only_first_arg = __fmt == _LIBCPP_STATICALLY_WIDEN(_CharT, "{}");
       __builtin_constant_p(__only_first_arg) && __only_first_arg) {
     if (auto __arg = __args.get(0); __builtin_constant_p(__arg.__type_)) {
-      return std::__visit_format_arg(
+      return std::__visit_format_arg( // TODO: Use __directly_visit_format_arg?
           []<class _Tp>(_Tp&& __argument) -> optional<basic_string<_CharT>> {
             if constexpr (is_same_v<remove_cvref_t<_Tp>, basic_string_view<_CharT>>) {
               return basic_string<_CharT>{__argument};

libcxx/include/__format/parser_std_format_spec.h

@@ -83,26 +83,21 @@ __parse_arg_id(_Iterator __begin, _Iterator __end, _ParseContext& __ctx) {
 
 template <class _Context>
 _LIBCPP_HIDE_FROM_ABI constexpr uint32_t __substitute_arg_id(basic_format_arg<_Context> __format_arg) {
-  // [format.string.std]/8
-  //   If the corresponding formatting argument is not of integral type...
-  // This wording allows char and bool too. LWG-3720 changes the wording to
-  //    If the corresponding formatting argument is not of standard signed or
-  //    unsigned integer type,
-  // 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.
+  // [format.string.std]/10
+  //   [...] The option is valid only if the corresponding formatting argument is of standard signed or unsigned integer
+  //   type. [...]
+  // This means 128-bit extented integer types are invalid here.
   return std::__visit_format_arg(
       [](auto __arg) -> uint32_t {
         using _Type = decltype(__arg);
         if constexpr (same_as<_Type, monostate>)
           std::__throw_format_error("The argument index value is too large for the number of arguments supplied");
 
-        // [format.string.std]/8
-        // If { arg-idopt } is used in a width or precision, the value of the
-        // corresponding formatting argument is used in its place. If the
-        // corresponding formatting argument is not of standard signed or unsigned
-        // integer type, or its value is negative for precision or non-positive for
-        // width, an exception of type format_error is thrown.
+        // [format.string.std]/10
+        // If { arg-idopt } is used in a width or precision option, the value of the corresponding formatting argument
+        // is used as the value of the option. The option is valid only if the corresponding formatting argument is of
+        // standard signed or unsigned integer type. If its value is negative, an exception of type format_error is
+        // thrown.
         //
         // When an integral is used in a format function, it is stored as one of
         // the types checked below. Other integral types are promoted. For example,