From f7ed65fa4a7e5b1ccaa775746dbe63deb6a91190 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Tue, 9 Jan 2024 05:54:18 -0800
Subject: [PATCH] Simplify format_arg_store

---
 include/fmt/core.h | 71 ++++++++++++++++------------------------------
 1 file changed, 25 insertions(+), 46 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 3bd312f2..dcfb5081 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1191,34 +1191,12 @@ template <typename Char> struct named_arg_info {
   int id;
 };
 
-template <typename Char>
-inline void init_named_args(named_arg_info<Char>*, int, int) {}
-
 template <typename T> struct is_named_arg : std::false_type {};
 template <typename T> struct is_statically_named_arg : std::false_type {};
 
 template <typename T, typename Char>
 struct is_named_arg<named_arg<Char, T>> : std::true_type {};
 
-template <typename Char, typename T, typename... Tail,
-          FMT_ENABLE_IF(!is_named_arg<T>::value)>
-void init_named_args(named_arg_info<Char>* named_args, int arg_count,
-                     int named_arg_count, const T&, const Tail&... args) {
-  init_named_args(named_args, arg_count + 1, named_arg_count, args...);
-}
-
-template <typename Char, typename T, typename... Tail,
-          FMT_ENABLE_IF(is_named_arg<T>::value)>
-void init_named_args(named_arg_info<Char>* named_args, int arg_count,
-                     int named_arg_count, const T& arg, const Tail&... args) {
-  named_args[named_arg_count++] = {arg.name, arg_count};
-  init_named_args(named_args, arg_count + 1, named_arg_count, args...);
-}
-
-template <typename... Args>
-FMT_CONSTEXPR FMT_INLINE void init_named_args(std::nullptr_t, int, int,
-                                              const Args&...) {}
-
 template <bool B = false> constexpr auto count() -> size_t { return B ? 1 : 0; }
 template <bool B1, bool B2, bool... Tail> constexpr auto count() -> size_t {
   return (B1 ? 1 : 0) + count<B2, Tail...>();
@@ -1596,46 +1574,47 @@ template <typename Context, size_t NUM_ARGS>
 using arg_t = conditional_t<NUM_ARGS <= max_packed_args, value<Context>,
                             basic_format_arg<Context>>;
 
+template <typename Char, typename T, FMT_ENABLE_IF(!is_named_arg<T>::value)>
+void init_named_arg(named_arg_info<Char>*, int& arg_index, int&, const T&) {
+  ++arg_index;
+}
+template <typename Char, typename T, FMT_ENABLE_IF(is_named_arg<T>::value)>
+void init_named_arg(named_arg_info<Char>* named_args, int& arg_index,
+                    int& named_arg_index, const T& arg) {
+  named_args[named_arg_index++] = {arg.name, arg_index++};
+}
+
 // An array of references to arguments. It can be implicitly converted to
 // `fmt::basic_format_args` for passing into type-erased formatting functions
 // such as `fmt::vformat`.
 template <typename Context, size_t NUM_ARGS, size_t NUM_NAMED_ARGS,
           unsigned long long DESC>
 struct format_arg_store {
-  static const bool is_packed = NUM_ARGS <= detail::max_packed_args;
-
-  using char_type = typename Context::char_type;
-  using value_type = arg_t<Context, NUM_ARGS>;
-
   // args_[0].named_args points to named_args to avoid bloating format_args.
   // +1 to workaround a bug in gcc 7.5 that causes duplicated-branches warning.
-  value_type args_[1 + (NUM_ARGS != 0 ? NUM_ARGS : +1)];
-  detail::named_arg_info<char_type> named_args[NUM_NAMED_ARGS];
+  arg_t<Context, NUM_ARGS> args[1 + (NUM_ARGS != 0 ? NUM_ARGS : +1)];
+  named_arg_info<typename Context::char_type> named_args[NUM_NAMED_ARGS];
 
   template <typename... T>
-  FMT_CONSTEXPR FMT_INLINE format_arg_store(T&... args)
-      : args_{{named_args, NUM_NAMED_ARGS},
-              detail::make_arg<is_packed, Context>(args)...} {
-    detail::init_named_args(named_args, 0, 0, args...);
-  }
-
-  FMT_CONSTEXPR FMT_INLINE auto args() const -> const value_type* {
-    return args_ + 1;
+  FMT_CONSTEXPR FMT_INLINE format_arg_store(T&... values)
+      : args{{named_args, NUM_NAMED_ARGS},
+             make_arg<NUM_ARGS <= max_packed_args, Context>(values)...} {
+    using dummy = int[];
+    int arg_index = 0, named_arg_index = 0;
+    (void)dummy{
+        0,
+        (init_named_arg(named_args, arg_index, named_arg_index, values), 0)...};
   }
 };
 
 // A specialization of format_arg_store without named arguments.
+// It is a plain struct to reduce binary size in debug mode.
 template <typename Context, size_t NUM_ARGS, unsigned long long DESC>
 struct format_arg_store<Context, NUM_ARGS, 0, DESC> {
-  using value_type = arg_t<Context, NUM_ARGS>;
-
   // +1 to workaround a bug in gcc 7.5 that causes duplicated-branches warning.
-  value_type args_[NUM_ARGS != 0 ? NUM_ARGS : +1];
-
-  FMT_CONSTEXPR FMT_INLINE auto args() const -> const value_type* {
-    return args_;
-  }
+  arg_t<Context, NUM_ARGS> args[NUM_ARGS != 0 ? NUM_ARGS : +1];
 };
+
 }  // namespace detail
 FMT_BEGIN_EXPORT
 
@@ -1808,14 +1787,14 @@ template <typename Context> class basic_format_args {
   constexpr basic_format_args(
       const detail::format_arg_store<Context, NUM_ARGS, NUM_NAMED_ARGS, DESC>&
           store)
-      : desc_(DESC), values_(store.args()) {}
+      : desc_(DESC), values_(store.args + (NUM_NAMED_ARGS != 0 ? 1 : 0)) {}
 
   template <size_t NUM_ARGS, size_t NUM_NAMED_ARGS, unsigned long long DESC,
             FMT_ENABLE_IF(NUM_ARGS > detail::max_packed_args)>
   constexpr basic_format_args(
       const detail::format_arg_store<Context, NUM_ARGS, NUM_NAMED_ARGS, DESC>&
           store)
-      : desc_(DESC), args_(store.args()) {}
+      : desc_(DESC), args_(store.args + (NUM_NAMED_ARGS != 0 ? 1 : 0)) {}
 
   /**
    \rst