Merge 2019-07 LWG Motion 32

P1208R6 Adopt source_location for C++20

Fixes #3036.

Author: zygoloid

source/lib-intro.tex

@@ -1214,12 +1214,13 @@
 \tcode{<semaphore>} \\
 \tcode{<set>} \\
 \tcode{<shared_mutex>} \\
+\tcode{<source_location>} \\
 \tcode{<span>} \\
 \tcode{<sstream>} \\
 \tcode{<stack>} \\
 \tcode{<stdexcept>} \\
-\tcode{<stop_token>} \\
 \columnbreak
+\tcode{<stop_token>} \\
 \tcode{<streambuf>} \\
 \tcode{<string>} \\
 \tcode{<string_view>} \\
@@ -1467,6 +1468,7 @@
 \ref{support.start.term} & Start and termination     & \tcode{<cstdlib>}          \\ \rowsep
 \ref{support.dynamic}    & Dynamic memory management & \tcode{<new>}              \\ \rowsep
 \ref{support.rtti}       & Type identification       & \tcode{<typeinfo>}         \\ \rowsep
+\ref{support.srcloc}     & Source location           & \tcode{<source_location>}  \\ \rowsep
 \ref{support.exception}  & Exception handling        & \tcode{<exception>}        \\ \rowsep
 \ref{support.initlist}   & Initializer lists         & \tcode{<initializer_list>} \\ \rowsep
 \ref{support.coroutine}  & Coroutines support        & \tcode{<coroutine>}        \\ \rowsep

source/support.tex

@@ -30,6 +30,7 @@
 \ref{support.start.term}  & Start and termination     &   \tcode{<cstdlib>}   \\ \rowsep
 \ref{support.dynamic}     & Dynamic memory management &   \tcode{<new>}       \\ \rowsep
 \ref{support.rtti}        & Type identification       &   \tcode{<typeinfo>}  \\ \rowsep
+\ref{support.srcloc}      & Source location           &   \tcode{<source_location>} \\ \rowsep
 \ref{support.exception}   & Exception handling        &   \tcode{<exception>} \\ \rowsep
 \ref{support.initlist}    & Initializer lists    & \tcode{<initializer_list>} \\ \rowsep
 \ref{cmp}                 & Comparisons               &   \tcode{<compare>}   \\ \rowsep
@@ -712,6 +713,8 @@
   \tcode{<memory>} \\ \rowsep
 \defnlibxname{cpp_lib_shared_timed_mutex}                   & \tcode{201402L} &
   \tcode{<shared_mutex>} \\ \rowsep
+\defnlibxname{cpp_lib_source_location}                      & \tcode{201907L} &
+  \tcode{<source_location>} \\ \rowsep
 \defnlibxname{cpp_lib_spaceship}                            & \tcode{201907L} &
   \tcode{<compare>} \\ \rowsep
 \defnlibxname{cpp_lib_string_udls}                          & \tcode{201304L} &
@@ -3178,6 +3181,214 @@
 An \impldef{return value of \tcode{bad_typeid::what}} \ntbs{}.
 \end{itemdescr}
 
+\rSec1[support.srcloc]{Class \tcode{source_location}}
+
+The header \tcode{<source_location>} defines the class \tcode{source_location} that provides a means to obtain source location information.
+
+\rSec2[source_location.syn]{Header \tcode{<source_location>} synopsis}
+\indexhdr{source_location}%
+\indexlibrary{\idxcode{source_location}}%
+
+\begin{codeblock}
+namespace std {
+  struct source_location {
+    // source location construction
+    static consteval source_location current() noexcept;
+    constexpr source_location() noexcept;
+
+    // source location field access
+    constexpr uint_least32_t line() const noexcept;
+    constexpr uint_least32_t column() const noexcept;
+    constexpr const char* file_name() const noexcept;
+    constexpr const char* function_name() const noexcept;
+
+  private:
+    uint_least32_t line_;               // \expos
+    uint_least32_t column_;             // \expos
+    const char* file_name_;             // \expos
+    const char* function_name_;         // \expos
+  };
+}
+\end{codeblock}
+
+\pnum
+The type \tcode{source_location} meets the
+\oldconcept{DefaultConstructible},
+\oldconcept{CopyConstructible},
+\oldconcept{Copy\-Assignable}, and
+\oldconcept{Destructible}
+requirements\iref{utility.arg.requirements}.
+Lvalues of type \tcode{source_location}
+are swappable\iref{swappable.requirements}.
+All of the following conditions are \tcode{true}:
+\begin{itemize}
+\item \tcode{is_nothrow_move_constructible_v<source_location>}
+\item \tcode{is_nothrow_move_assignable_v<source_location>}
+\item \tcode{is_nothrow_swappable_v<source_location>}
+\end{itemize}
+\begin{note}
+The intent of \tcode{source_location} is
+to have a small size and efficient copying.
+\end{note}
+
+\pnum
+The data members \tcode{file_name_} and \tcode{function_name_}
+always each refer to an \ntbs{}.
+
+\pnum
+The copy/move constructors and the copy/move assignment operators of
+\tcode{source_location} meet the following postconditions:
+Given two objects  \tcode{lhs} and \tcode{rhs} of type \tcode{source_location},
+where \tcode{lhs} is a copy/move result of \tcode{rhs}, and
+where \tcode{rhs_p} is a value denoting the state of \tcode{rhs}
+before the corresponding copy/move operation,
+then each of the following conditions is \tcode{true}:
+\begin{itemize}
+\item \tcode{strcmp(lhs.file_name(), rhs_p.file_name()) == 0}
+\item \tcode{strcmp(lhs.function_name(), rhs_p.function_name()) == 0}
+\item \tcode{lhs.line() == rhs_p.line()}
+\item \tcode{lhs.column() == rhs_p.column()}
+\end{itemize}
+
+\rSec2[support.srcloc.cons]{Creation}
+
+\begin{itemdecl}
+static consteval source_location current() noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+\returns
+\begin{itemize}
+\item
+  When invoked by a function call
+  whose \grammarterm{postfix-expression} is
+  a (possibly parenthesized) \grammarterm{id-expression} naming \tcode{current},
+  returns a \tcode{source_location} with an implementation-defined value.
+  The value should be affected by \tcode{\#line}\iref{cpp.line}
+  in the same manner as for \mname{LINE} and \mname{FILE}.
+  The values of the exposition-only data members
+  of the returned \tcode{source_location} object
+  are indicated in \tref{support.srcloc.current}.
+
+\begin{libefftabvalue}
+  {Value of object returned by \tcode{current}}
+  {support.srcloc.current}
+\tcode{line_}    &
+  A presumed line number\iref{cpp.predefined}.
+  Line numbers are presumed to be 1-indexed;
+  however, an implementation is encouraged to use 0
+  when the line number is unknown. \\ \rowsep
+\tcode{column_}  &
+  An implementation-defined value denoting
+  some offset from the start of the line denoted by \tcode{line_}.
+  Column numbers are presumed to be 1-indexed;
+  however, an implementation is encouraged to use 0
+  when the column number is unknown. \\ \rowsep
+\tcode{file_name_} &
+  A presumed name of the current source file\iref{cpp.predefined} as an \ntbs{}.
+  \\ \rowsep
+\tcode{function_name_} &
+  A name of the current function
+  such as in \mname{func}\iref{dcl.fct.def.general} if any,
+  an empty string otherwise. \\
+\end{libefftabvalue}
+
+\item
+  Otherwise, when invoked in some other way, returns a
+  \tcode{source_location} whose data members are initialized
+  with valid but unspecified values.
+\end{itemize}
+
+\pnum
+\remarks
+When a default member initializer
+is used to initialize a non-static data member,
+any calls to \tcode{current} should correspond to the location
+of the constructor or aggregate initialization that initializes the member.
+
+\pnum
+\begin{note}
+When used as a default argument\iref{dcl.fct.default},
+the value of the \tcode{source_location} will be
+the location of the call to \tcode{current} at the call site.
+\end{note}
+\end{itemdescr}
+
+\pnum
+\begin{example}
+\begin{codeblock}
+struct s {
+  source_location member = source_location::current();
+  int other_member;
+  s(source_location loc = source_location::current())
+    : member(loc)               // values of \tcode{member} refer to the location of the calling function\iref{dcl.fct.default}
+  {}
+  s(int blather) :              // values of \tcode{member} refer to this location
+    other_member(blather)
+  {}
+  s(double)                     // values of \tcode{member} refer to this location
+  {}
+};
+void f(source_location a = source_location::current()) {
+  source_location b = source_location::current();       // values in \tcode{b} refer to this line
+}
+
+void g() {
+  f();                          // \tcode{f}'s first argument corresponds to this line of code
+
+  source_location c = source_location::current();
+  f(c);                         // \tcode{f}'s first argument gets the same values as \tcode{c}, above
+}
+\end{codeblock}
+\end{example}
+
+\begin{itemdecl}
+constexpr source_location() noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+
+\pnum
+\Fundesc{Effects}
+The data members are initialized with valid but unspecified values.
+\end{itemdescr}
+
+\rSec2[support.srcloc.access]{Field access}
+
+\begin{itemdecl}
+constexpr uint_least32_t line() const noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+\returns \tcode{line_}.
+\end{itemdescr}
+
+\begin{itemdecl}
+constexpr uint_least32_t column() const noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{column_}.
+\end{itemdescr}
+
+\begin{itemdecl}
+constexpr const char* file_name() const noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{file_name_}.
+\end{itemdescr}
+
+\begin{itemdecl}
+constexpr const char* function_name() const noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{function_name_}.
+\end{itemdescr}
+
 \rSec1[support.exception]{Exception handling}
 
 \pnum