[variant.visit], [tuple.apply], [futures.task.members] add cross-references for INVOKE to [func.require]

Fixes #1480.

Author: jensmaurer

source/threads.tex

@@ -5038,7 +5038,7 @@
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)}, where \tcode{t$_1$, t$_2$, $\dotsc$, t$_N$} are values
+\tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)} (\ref{func.require}), where \tcode{t$_1$, t$_2$, $\dotsc$, t$_N$} are values
 of the corresponding types in \tcode{ArgTypes...}, shall be a valid expression. Invoking
 a copy of \tcode{f} shall behave the same as invoking \tcode{f}.
 
@@ -5160,7 +5160,7 @@
 
 \begin{itemdescr}
 \pnum
-\effects As if by \tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)},
+\effects As if by \tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)} (\ref{func.require}),
 where \tcode{f} is the
 stored task of \tcode{*this} and
 \tcode{t$_1$, t$_2$, $\dotsc$, t$_N$} are the values in \tcode{args...}. If the task returns normally,
@@ -5190,7 +5190,7 @@
 
 \begin{itemdescr}
 \pnum
-\effects As if by \tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)},
+\effects As if by \tcode{\placeholdernc{INVOKE}<R>(f, t$_1$, t$_2$, $\dotsc$, t$_N$)} (\ref{func.require}),
 where \tcode{f} is the stored task and
 \tcode{t$_1$, t$_2$, $\dotsc$, t$_N$} are the values in \tcode{args...}. If the task returns normally,
 the return value is stored as the asynchronous result in the shared state of

source/utilities.tex

@@ -2130,7 +2130,7 @@
 template <class F, class Tuple, size_t... I>
 constexpr decltype(auto)
     apply_impl(F&& f, Tuple&& t, index_sequence<I...>) {                // exposition only
-  return @\placeholdernc{INVOKE}@(std::forward<F>(f), std::get<I>(std::forward<Tuple>(t))...);
+  return @\placeholdernc{INVOKE}@(std::forward<F>(f), std::get<I>(std::forward<Tuple>(t))...);  // see \ref{func.require}
 }
 \end{codeblock}
 Equivalent to:
@@ -5288,7 +5288,7 @@
 \pnum
 \effects
 Let \tcode{is...} be \tcode{vars.index()...}. Returns \tcode{\placeholdernc{INVOKE}(forward<Visitor>(vis), get<is>(}\brk{}
-\tcode{forward<Variants>(vars))...);}.
+\tcode{forward<Variants>(vars))...);} (\ref{func.require}).
 
 \pnum
 \remarks