From 45b673f2265b79f4b07584d2d39df8d2e1a63c3b Mon Sep 17 00:00:00 2001
From: Jens Maurer <Jens.Maurer@gmx.net>
Date: Thu, 7 Oct 2021 22:16:34 +0200
Subject: [PATCH 1/2] P2418R2 Add support for std::generator-like types to
 std::format

---
 source/compatibility.tex |  18 +++++
 source/utilities.tex     | 164 ++++++++++++++++++++++++---------------
 2 files changed, 120 insertions(+), 62 deletions(-)

diff --git a/source/compatibility.tex b/source/compatibility.tex
index d4472f8f5d..76b01589e8 100644
--- a/source/compatibility.tex
+++ b/source/compatibility.tex
@@ -76,6 +76,24 @@
                                                         // previously threw \tcode{format_error}
 \end{codeblock}
 
+\diffref{format}
+\change
+Signature changes: \tcode{format}, \tcode{format_to}, \tcode{format_to_n},
+\tcode{formatted_size}.
+\rationale
+Enable formatting of views that are neither const-iterable nor copyable.
+\effect
+Valid \CppXX{} code that passes bit fields to formatting functions
+may become ill-formed. For example:
+\begin{codeblock}
+struct tiny {
+  int bit: 1;
+};
+
+auto t = tiny();
+std::format("{}", t.bit);       // ill-formed, previously returned \tcode{"0"}
+\end{codeblock}
+
 \rSec1[diff.cpp17]{\Cpp{} and ISO \CppXVII{}}
 
 \rSec2[diff.cpp17.general]{General}
diff --git a/source/utilities.tex b/source/utilities.tex
index 17ed34b9e7..683e0cc705 100644
--- a/source/utilities.tex
+++ b/source/utilities.tex
@@ -19672,13 +19672,13 @@
 
   // \ref{format.functions}, formatting functions
   template<class... Args>
-    string format(@\exposid{format-string}@<Args...> fmt, const Args&... args);
+    string format(@\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    wstring format(@\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    wstring format(@\exposid{wformat-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    string format(const locale& loc, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+    string format(const locale& loc, @\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    wstring format(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    wstring format(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 
   string vformat(string_view fmt, format_args args);
   wstring vformat(wstring_view fmt, wformat_args args);
@@ -19686,13 +19686,13 @@
   wstring vformat(const locale& loc, wstring_view fmt, wformat_args args);
 
   template<class Out, class... Args>
-    Out format_to(Out out, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+    Out format_to(Out out, @\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class Out, class... Args>
-    Out format_to(Out out, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    Out format_to(Out out, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
   template<class Out, class... Args>
-    Out format_to(Out out, const locale& loc, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+    Out format_to(Out out, const locale& loc, @\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class Out, class... Args>
-    Out format_to(Out out, const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    Out format_to(Out out, const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 
   template<class Out>
     Out vformat_to(Out out, string_view fmt, format_args args);
@@ -19709,27 +19709,27 @@
   };
   template<class Out, class... Args>
     format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
-                                        @\exposid{format-string}@<Args...> fmt, const Args&... args);
+                                        @\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class Out, class... Args>
     format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
-                                        @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+                                        @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
   template<class Out, class... Args>
     format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                         const locale& loc, @\exposid{format-string}@<Args...> fmt,
-                                        const Args&... args);
+                                        Args&&... args);
   template<class Out, class... Args>
     format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                         const locale& loc, @\exposid{wformat-string}@<Args...> fmt,
-                                        const Args&... args);
+                                        Args&&... args);
 
   template<class... Args>
-    size_t formatted_size(@\exposid{format-string}@<Args...> fmt, const Args&... args);
+    size_t formatted_size(@\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    size_t formatted_size(@\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    size_t formatted_size(@\exposid{wformat-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    size_t formatted_size(const locale& loc, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+    size_t formatted_size(const locale& loc, @\exposid{format-string}@<Args...> fmt, Args&&... args);
   template<class... Args>
-    size_t formatted_size(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+    size_t formatted_size(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 
   // \ref{format.formatter}, formatter
   template<class T, class charT = char> struct formatter;
@@ -19751,10 +19751,10 @@
 
   template<class Context = format_context, class... Args>
     @\exposid{format-arg-store}@<Context, Args...>
-      make_format_args(const Args&... fmt_args);
+      make_format_args(Args&&... fmt_args);
   template<class... Args>
     @\exposid{format-arg-store}@<wformat_context, Args...>
-      make_wformat_args(const Args&... args);
+      make_wformat_args(Args&&... args);
 
   // \ref{format.error}, class \tcode{format_error}
   class format_error;
@@ -20513,7 +20513,7 @@
 \indexlibraryglobal{format}%
 \begin{itemdecl}
 template<class... Args>
-  string format(@\exposid{format-string}@<Args...> fmt, const Args&... args);
+  string format(@\exposid{format-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20528,7 +20528,7 @@
 \indexlibraryglobal{format}%
 \begin{itemdecl}
 template<class... Args>
-  wstring format(@\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  wstring format(@\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20543,7 +20543,7 @@
 \indexlibraryglobal{format}%
 \begin{itemdecl}
 template<class... Args>
-  string format(const locale& loc, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+  string format(const locale& loc, @\exposid{format-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20558,7 +20558,7 @@
 \indexlibraryglobal{format}%
 \begin{itemdecl}
 template<class... Args>
-  wstring format(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  wstring format(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20594,7 +20594,7 @@
 \indexlibraryglobal{format_to}%
 \begin{itemdecl}
 template<class Out, class... Args>
-  Out format_to(Out out, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+  Out format_to(Out out, @\exposid{format-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20609,7 +20609,7 @@
 \indexlibraryglobal{format_to}%
 \begin{itemdecl}
 template<class Out, class... Args>
-  Out format_to(Out out, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  Out format_to(Out out, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20624,7 +20624,7 @@
 \indexlibraryglobal{format_to}%
 \begin{itemdecl}
 template<class Out, class... Args>
-  Out format_to(Out out, const locale& loc, @\exposid{format-string}@<Args...>  fmt, const Args&... args);
+  Out format_to(Out out, const locale& loc, @\exposid{format-string}@<Args...>  fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20639,7 +20639,7 @@
 \indexlibraryglobal{format_to}%
 \begin{itemdecl}
 template<class Out, class... Args>
-  Out format_to(Out out, const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  Out format_to(Out out, const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20699,18 +20699,18 @@
 \begin{itemdecl}
 template<class Out, class... Args>
   format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
-                                      @\exposid{format-string}@<Args...> fmt, const Args&... args);
+                                      @\exposid{format-string}@<Args...> fmt, Args&&... args);
 template<class Out, class... Args>
   format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
-                                      @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+                                      @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 template<class Out, class... Args>
   format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                       const locale& loc, @\exposid{format-string}@<Args...> fmt,
-                                      const Args&... args);
+                                      Args&&... args);
 template<class Out, class... Args>
   format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                       const locale& loc, @\exposid{wformat-string}@<Args...> fmt,
-                                      const Args&... args);
+                                      Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20731,8 +20731,8 @@
 \pnum
 \expects
 \tcode{Out} models \tcode{\libconcept{output_iterator}<const charT\&>}, and
-\tcode{formatter<}$\tcode{T}_i$\tcode{, charT>}
-meets the \newoldconcept{Formatter} requirements\iref{formatter.requirements}
+\tcode{formatter<}$\tcode{remove_cvref_t<T}_i$\tcode{>, charT>}
+meets the \newoldconcept{BasicFormatter} requirements\iref{formatter.requirements}
 for each $\tcode{T}_i$ in \tcode{Args}.
 
 \pnum
@@ -20755,13 +20755,13 @@
 \indexlibraryglobal{formatted_size}%
 \begin{itemdecl}
 template<class... Args>
-  size_t formatted_size(@\exposid{format-string}@<Args...> fmt, const Args&... args);
+  size_t formatted_size(@\exposid{format-string}@<Args...> fmt, Args&&... args);
 template<class... Args>
-  size_t formatted_size(@\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  size_t formatted_size(@\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 template<class... Args>
-  size_t formatted_size(const locale& loc, @\exposid{format-string}@<Args...> fmt, const Args&... args);
+  size_t formatted_size(const locale& loc, @\exposid{format-string}@<Args...> fmt, Args&&... args);
 template<class... Args>
-  size_t formatted_size(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, const Args&... args);
+  size_t formatted_size(const locale& loc, @\exposid{wformat-string}@<Args...> fmt, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -20770,8 +20770,8 @@
 
 \pnum
 \expects
-\tcode{formatter<}$\tcode{T}_i$\tcode{, charT>}
-meets the \newoldconcept{Formatter} requirements\iref{formatter.requirements}
+\tcode{formatter<}$\tcode{remove_cvref_t<T}_i$\tcode{>, charT>}
+meets the \newoldconcept{BasicFormatter} requirements\iref{formatter.requirements}
 for each $\tcode{T}_i$ in \tcode{Args}.
 
 \pnum
@@ -20791,7 +20791,7 @@
 \rSec3[formatter.requirements]{Formatter requirements}
 
 \pnum
-A type \tcode{F} meets the \defnnewoldconcept{Formatter} requirements if:
+A type \tcode{F} meets the \defnnewoldconcept{BasicFormatter} requirements if:
 \begin{itemize}
 \item
 it meets the
@@ -20807,14 +20807,20 @@
 it is swappable\iref{swappable.requirements} for lvalues, and
 
 \item
-the expressions shown in \tref{formatter} are valid and
+the expressions shown in \tref{formatter.basic} are valid and
 have the indicated semantics.
 \end{itemize}
 
+\pnum
+A type \tcode{F} meets the \defnnewoldconcept{Formatter} requirements
+if it meets the \newoldconcept{BasicFormatter} requirements and
+the expressions shown in \tref{formatter} are valid and
+have the indicated semantics.
+
 \pnum
 Given character type \tcode{charT}, output iterator type
 \tcode{Out}, and formatting argument type \tcode{T},
-in \tref{formatter}:
+in \tref{formatter.basic} and \tref{formatter}:
 \begin{itemize}
 \item \tcode{f} is a value of type \tcode{F},
 \item \tcode{u} is an lvalue of type \tcode{T},
@@ -20832,7 +20838,7 @@
 \tcode{pc.begin() == pc.end()} or
 \tcode{*pc.begin() == '\}'}.
 
-\begin{concepttable}{\newoldconcept{Formatter} requirements}{formatter}
+\begin{concepttable}{\newoldconcept{BasicFormatter} requirements}{formatter.basic}
 {p{1.2in}p{1in}p{2.9in}}
 \topline
 \hdstyle{Expression} & \hdstyle{Return type} & \hdstyle{Requirement} \\ \capsep
@@ -20850,10 +20856,28 @@
 Stores the parsed format specifiers in \tcode{*this} and
 returns an iterator past the end of the parsed range.
 \\ \rowsep
+\tcode{f.format(u, fc)} &
+\tcode{FC::iterator} &
+Formats \tcode{u} according to the specifiers stored in \tcode{*this},
+writes the output to \tcode{fc.out()}, and
+returns an iterator past the end of the output range.
+The output shall only depend on
+\tcode{u},
+\tcode{fc.locale()},
+\tcode{fc.arg(n)} for any value \tcode{n} of type \tcode{size_t},
+and the range \range{pc.begin()}{pc.end()}
+from the last call to \tcode{f.parse(pc)}.
+\\
+\end{concepttable}
+
+\begin{concepttable}{\newoldconcept{Formatter} requirements}{formatter}
+{p{1.2in}p{1in}p{2.9in}}
+\topline
+\hdstyle{Expression} & \hdstyle{Return type} & \hdstyle{Requirement} \\ \capsep
 \tcode{f.format(t, fc)} &
 \tcode{FC::iterator} &
 Formats \tcode{t} according to the specifiers stored in \tcode{*this},
-writes the output to \tcode{fc.out()} and
+writes the output to \tcode{fc.out()}, and
 returns an iterator past the end of the output range.
 The output shall only depend on
 \tcode{t},
@@ -20881,10 +20905,6 @@
 Let \tcode{charT} be either \tcode{char} or \keyword{wchar_t}.
 Each specialization of \tcode{formatter} is either enabled or disabled,
 as described below.
-\begin{note}
-Enabled specializations meet the \newoldconcept{Formatter} requirements,
-and disabled specializations do not.
-\end{note}
 Each header that declares the template \tcode{formatter}
 provides the following enabled specializations:
 \begin{itemize}
@@ -20958,6 +20978,7 @@
 \pnum
 If the library provides an explicit or partial specialization of
 \tcode{formatter<T, charT>}, that specialization is enabled
+and meets the \newoldconcept{Formatter} requirements
 except as noted otherwise.
 
 \pnum
@@ -20973,7 +20994,7 @@
 
 \pnum
 An enabled specialization \tcode{formatter<T, charT>} meets the
-\newoldconcept{Formatter} requirements\iref{formatter.requirements}.
+\newoldconcept{BasicFormatter} requirements\iref{formatter.requirements}.
 \begin{example}
 \begin{codeblock}
 #include <format>
@@ -21309,7 +21330,7 @@
             const char_type*, basic_string_view<char_type>,
             const void*, handle> value;                                         // \expos
 
-    template<class T> explicit basic_format_arg(const T& v) noexcept;           // \expos
+    template<class T> explicit basic_format_arg(T&& v) noexcept;                // \expos
     explicit basic_format_arg(float n) noexcept;                                // \expos
     explicit basic_format_arg(double n) noexcept;                               // \expos
     explicit basic_format_arg(long double n) noexcept;                          // \expos
@@ -21356,7 +21377,7 @@
 \end{itemdescr}
 
 \begin{itemdecl}
-template<class T> explicit basic_format_arg(const T& v) noexcept;
+template<class T> explicit basic_format_arg(T&& v) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -21364,16 +21385,16 @@
 \constraints
 The template specialization
 \begin{codeblock}
-typename Context::template formatter_type<T>
+typename Context::template formatter_type<remove_cvref_t<T>>
 \end{codeblock}
-meets the \newoldconcept{Formatter} requirements\iref{formatter.requirements}.
+meets the \newoldconcept{BasicFormatter} requirements\iref{formatter.requirements}.
 The extent to which an implementation determines that
-the specialization meets the \newoldconcept{Formatter} requirements
+the specialization meets the \newoldconcept{BasicFormatter} requirements
 is unspecified,
 except that as a minimum the expression
 \begin{codeblock}
-typename Context::template formatter_type<T>()
-  .format(declval<const T&>(), declval<Context&>())
+typename Context::template formatter_type<remove_cvref_t<T>>()
+  .format(declval<T&>(), declval<Context&>())
 \end{codeblock}
 shall be well-formed when treated as an unevaluated operand.
 
@@ -21518,7 +21539,7 @@
     void (*format_)(basic_format_parse_context<char_type>&,
                     Context&, const void*);                     // \expos
 
-    template<class T> explicit handle(const T& val) noexcept;   // \expos
+    template<class T> explicit handle(T&& val) noexcept;        // \expos
 
     friend class basic_format_arg<Context>;                     // \expos
 
@@ -21530,10 +21551,28 @@
 
 \indexlibraryctor{basic_format_arg::handle}%
 \begin{itemdecl}
-template<class T> explicit handle(const T& val) noexcept;
+template<class T> explicit handle(T&& val) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let
+\begin{itemize}
+\item
+\tcode{TD} be \tcode{remove_cvref_t<T>},
+\item
+\exposid{const-formattable} be \tcode{true} if
+\tcode{typename Context::template formatter_type<TD>()\newline .format(declval<const TD\&>(), declval<Context\&>())} is well-formed, otherwise \tcode{false},
+\item
+\tcode{TQ} be \tcode{const TD} if \exposid{const-formattable} is \tcode{true}
+and \tcode{TD} otherwise.
+\end{itemize}
+
+\pnum
+\mandates
+\tcode{\exposid{const-formattable} || !is_const_v<remove_reference_t<T>>} is
+\tcode{true}.
+
 \pnum
 \effects
 Initializes
@@ -21542,9 +21581,10 @@
 \begin{codeblock}
 [](basic_format_parse_context<char_type>& parse_ctx,
    Context& format_ctx, const void* ptr) {
-  typename Context::template formatter_type<T> f;
+  typename Context::template formatter_type<TD> f;
   parse_ctx.advance_to(f.parse(parse_ctx));
-  format_ctx.advance_to(f.format(*static_cast<const T*>(ptr), format_ctx));
+  format_ctx.advance_to(f.format(*const_cast<TQ*>(static_cast<const TD*>(ptr)),
+                                 format_ctx));
 }
 \end{codeblock}
 \end{itemdescr}
@@ -21589,7 +21629,7 @@
 \indexlibraryglobal{make_format_args}%
 \begin{itemdecl}
 template<class Context = format_context, class... Args>
-  @\exposid{format-arg-store}@<Context, Args...> make_format_args(const Args&... fmt_args);
+  @\exposid{format-arg-store}@<Context, Args...> make_format_args(Args&&... fmt_args);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -21597,7 +21637,7 @@
 \expects
 The type
 \tcode{typename Context::template formatter_type<}$\tcode{T}_i$\tcode{>}
-meets the \newoldconcept{Formatter} requirements\iref{formatter.requirements}
+meets the \newoldconcept{BasicFormatter} requirements\iref{formatter.requirements}
 for each $\tcode{T}_i$ in \tcode{Args}.
 
 \pnum
@@ -21610,7 +21650,7 @@
 \indexlibraryglobal{make_wformat_args}%
 \begin{itemdecl}
 template<class... Args>
-  @\exposid{format-arg-store}@<wformat_context, Args...> make_wformat_args(const Args&... args);
+  @\exposid{format-arg-store}@<wformat_context, Args...> make_wformat_args(Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}

From b094cb62a059fe19b632ec22c37b3a306fa897e3 Mon Sep 17 00:00:00 2001
From: Jens Maurer <Jens.Maurer@gmx.net>
Date: Mon, 18 Oct 2021 12:34:19 +0200
Subject: [PATCH 2/2] [diff.cpp20.utilities] Rephrase to avoid undefined term
 'const-iterable'

---
 source/compatibility.tex | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/source/compatibility.tex b/source/compatibility.tex
index 76b01589e8..6c88c853a6 100644
--- a/source/compatibility.tex
+++ b/source/compatibility.tex
@@ -81,7 +81,9 @@
 Signature changes: \tcode{format}, \tcode{format_to}, \tcode{format_to_n},
 \tcode{formatted_size}.
 \rationale
-Enable formatting of views that are neither const-iterable nor copyable.
+Enable formatting of views
+that do not support iteration when const-qualified and
+are not copyable.
 \effect
 Valid \CppXX{} code that passes bit fields to formatting functions
 may become ill-formed. For example: