Merge 2025-06 CWG Motion 9

P3096R12 Function Parameter Reflection in Reflection for C++26

Author: tkoeppe

source/basic.tex

@@ -5611,6 +5611,7 @@
 \item a variable\iref{basic.pre},
 \item a structured binding\iref{dcl.struct.bind},
 \item a function\iref{dcl.fct},
+\item a function parameter\iref{dcl.fct},
 \item an enumerator\iref{dcl.enum},
 \item an annotation\iref{dcl.attr.grammar},
 \item a type alias\iref{dcl.typedef},

source/meta.tex

@@ -2683,6 +2683,11 @@
   consteval bool is_move_assignment(info r);
   consteval bool is_destructor(info r);
 
+  consteval bool is_function_parameter(info r);
+  consteval bool is_explicit_object_parameter(info r);
+  consteval bool has_default_argument(info r);
+  consteval bool has_ellipsis_parameter(info r);
+
   consteval bool is_template(info r);
   consteval bool is_function_template(info r);
   consteval bool is_variable_template(info r);
@@ -2715,6 +2720,9 @@
   consteval bool has_template_arguments(info r);
   consteval info template_of(info r);
   consteval vector<info> template_arguments_of(info r);
+  consteval vector<info> parameters_of(info r);
+  consteval info variable_of(info r);
+  consteval info return_type_of(info r);
 
   // \ref{meta.reflection.access.context}, access control context
   struct access_context;
@@ -3238,6 +3246,47 @@
   operator function template,
   or conversion function template.
   Otherwise, \tcode{false}.
+\item
+  Otherwise, if \tcode{r} represents the $i^\text{th}$ parameter of a function $F$
+  that is an (implicit or explicit) specialization of a templated function $T$
+  and the $i^\text{th}$ parameter of the instantiated declaration of $T$
+  whose template arguments are those of $F$ would be instantiated from a pack,
+  then \tcode{false}.
+\item
+  Otherwise, if \tcode{r} represents the parameter $P$ of  a function $F$,
+  then let $S$ be the set of declarations,
+  ignoring any explicit instantiations,
+  that precede some point in the evaluation context
+  and that declare either $F$ or a templated function
+  of which $F$ is a specialization;
+  \tcode{true} if
+  \begin{itemize}
+  \item
+    there is a declaration $D$ in $S$ that introduces a name $N$ for either $P$
+    or the parameter corresponding to $P$
+    in the templated function that $D$ declares and
+  \item
+    no declaration in $S$ does so using any name other than $N$.
+  \end{itemize}
+  Otherwise, \tcode{false}.
+  \begin{example}
+\begin{codeblock}
+void fun(int);
+constexpr std::meta::info r = parameters_of(^^fun)[0];
+static_assert(!has_identifier(r));
+
+void fun(int x);
+static_assert(has_identifier(r));
+
+void fun(int x);
+static_assert(has_identifier(r));
+
+void poison() {
+  void fun(int y);
+}
+static_assert(!has_identifier(r));
+\end{codeblock}
+  \end{example}
 \item
   Otherwise, if \tcode{r} represents a variable,
   then \tcode{false} if the declaration of that variable
@@ -3298,6 +3347,15 @@
 \item
   Otherwise, if \tcode{r} represents a literal operator or literal operator template,
   then the \grammarterm{ud-suffix} of the operator or operator template.
+\item
+  Otherwise, if \tcode{r} represents the parameter $P$ of a function $F$,
+  then let $S$ be the set of declarations,
+  ignoring any explicit instantiations,
+  that precede some point in the evaluation context
+  and that declare either $F$
+  or a templated function of which $F$ is a specialization;
+  the name that was introduced by a declaration in $S$
+  for the parameter corresponding to $P$.
 \item
   Otherwise, if \tcode{r} represents an entity,
   then the identifier introduced by the declaration of that entity.
@@ -3378,8 +3436,9 @@
 enumerator,
 non-static data member,
 unnamed bit-field,
-direct base class relationship, or
-data member description.
+direct base class relationship,
+data member description, or
+function parameter.
 Otherwise, \tcode{false}.
 \end{itemdescr}
 
@@ -3397,7 +3456,11 @@
 \returns
 \begin{itemize}
 \item
-  If \tcode{r} represents a
+  If \tcode{r} represents the $i^\text{th}$ parameter of a function $F$,
+  then the $i^\text{th}$ type
+  in the parameter-type-list of $F$\iref{dcl.fct}.
+\item
+  Otherwise, if \tcode{r} represents a
   value,
   object,
   variable,
@@ -3968,6 +4031,70 @@
 Otherwise, \tcode{false}.
 \end{itemdescr}
 
+\indexlibraryglobal{is_function_parameter}%
+\begin{itemdecl}
+consteval bool is_function_parameter(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true} if \tcode{r} represents a function parameter.
+Otherwise, \tcode{false}.
+\end{itemdescr}
+
+\indexlibraryglobal{is_explicit_object_parameter}%
+\begin{itemdecl}
+consteval bool is_explicit_object_parameter(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true} if \tcode{r} represents a function parameter
+that is an explicit object parameter\iref{dcl.fct}.
+Otherwise, \tcode{false}.
+\end{itemdescr}
+
+\indexlibraryglobal{has_default_argument}%
+\begin{itemdecl}
+consteval bool has_default_argument(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+If \tcode{r} represenst a parameter $P$ of a function $F$, then:
+\begin{itemize}
+\item
+  If $F$ is a specialization of a templated function $T$,
+  then \tcode{true} if there exists a declaration $D$ of $T$
+  that precedes some point in the evaluation context
+  and $D$ specifies a default argument
+  for the parameter of $T$ corresponding to $P$.
+  Otherwise, \tcode{false}.
+\item
+  Otherwise, if there exists a declaration $D$ of $F$
+  that precedes some point in the evaluation context
+  and $D$ specifies a default argument for $P$,
+  then \tcode{true}.
+\end{itemize}
+Otherwise, \tcode{false}.
+\end{itemdescr}
+
+\indexlibraryglobal{has_ellipsis_parameter}%
+\begin{itemdecl}
+consteval bool has_ellipsis_parameter(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true} if \tcode{r} represents a function type
+that has an ellipsis in its parameter-type-list\iref{dcl.fct}.
+Otherwise, \tcode{false}.
+\end{itemdescr}
+
 \indexlibraryglobal{is_template}%
 \begin{itemdecl}
 consteval bool is_template(info r);
@@ -4266,7 +4393,7 @@
 A \tcode{vector} containing reflections
 of the template arguments
 of the template specialization represented by \tcode{r},
-in the order they appear in the corresponding template argument list.
+in the order in which they appear in the corresponding template argument list.
 For a given template argument $A$,
 its corresponding reflection $R$ is determined as follows:
 \begin{itemize}
@@ -4325,6 +4452,72 @@
 \end{example}
 \end{itemdescr}
 
+\indexlibraryglobal{parameters_of}%
+\begin{itemdecl}
+consteval vector<info> parameters_of(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constantwhen
+\tcode{r} represents a function or a function type.
+
+\pnum
+\returns
+\begin{itemize}
+\item
+  If \tcode{r} represents a function $F$,
+  then a \tcode{vector} containing reflections of the parameters of $F$,
+  in the order in which they appear in a declaration of $F$.
+\item
+  Otherwise, \tcode{r} represents a function type $T$;
+  a \tcode{vector} containing reflections of the types
+  in parameter-type-list\iref{dcl.fct} of $T$,
+  in the order in which they appear in the parameter-type-list.
+\end{itemize}
+\end{itemdescr}
+
+\indexlibraryglobal{variable_of}%
+\begin{itemdecl}
+consteval info variable_of(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constantwhen
+\begin{itemize}
+\item
+  \tcode{r} represents a parameter of a function $F$ and
+\item
+  there is a point $P$ in the evaluation context
+  for which the innermost non-block scope enclosing $P$
+  is the function parameter scope\iref{basic.scope.param}
+  associated with $F$.
+\end{itemize}
+
+\pnum
+\returns
+The reflection of the parameter variable corresponding to \tcode{r}.
+\end{itemdescr}
+
+\indexlibraryglobal{return_type_of}%
+\begin{itemdecl}
+consteval info return_type_of(info r);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constantwhen
+Either \tcode{r} represents a function
+and \tcode{\exposid{has-type}(r)} is \tcode{true}
+or \tcode{r} represents a function type.
+
+\pnum
+\returns
+The reflection of the return type
+of the function or function type represented by \tcode{r}.
+\end{itemdescr}
+
 \rSec2[meta.reflection.access.context]{Access control context}
 
 \pnum