CWG2293 Requirements for simple-template-id used as a class-name

Author: tkoeppe

source/basic.tex

@@ -614,7 +614,7 @@
 \indextext{region!declarative}%
 \indextext{scope!potential}%
 \defn{declarative region}, which is the largest part of the program
-in which that name is \defn{valid}, that is, in which that name may
+in which that name is valid, that is, in which that name may
 be used as an unqualified name to refer to the same entity. In general,
 each particular name is valid only within some possibly discontiguous
 portion of program text called its \defn{scope}. To determine the

source/templates.tex

@@ -962,6 +962,45 @@
 A \grammarterm{template-id} that names an alias template
 specialization is a \grammarterm{type-name}.
 
+\pnum
+A \grammarterm{template-id} is \defnx{valid}{\idxgram{template-id}!valid} if
+\begin{itemize}
+\item
+  there are at most as many arguments as there are parameters
+  or a parameter is a template parameter pack\iref{temp.variadic},
+
+\item
+  there is an argument for each non-deducible non-pack parameter
+  that does not have a default \grammarterm{template-argument},
+
+\item
+  each \grammarterm{template-argument} matches the corresponding
+  \grammarterm{template-parameter}\iref{temp.arg},
+
+\item
+  substitution of each template argument into the following
+  template parameters (if any) succeeds, and
+
+\item
+  if the \grammarterm{template-id} is non-dependent,
+  the associated constraints are satisfied as specified in the next paragraph.
+\end{itemize}
+A \grammarterm{simple-template-id} shall be valid unless it names a
+function template specialization\iref{temp.deduct}.
+\begin{example}
+\begin{codeblock}
+template<class T, T::type n = 0> class X;
+struct S {
+  using type = int;
+};
+using T1 = X<S, int, int>;      // error: too many arguments
+using T2 = X<>;                 // error: no default argument for first template parameter
+using T3 = X<1>;                // error: value \tcode{1} does not match type-parameter
+using T4 = X<int>;              // error: substitution failure for second template parameter
+using T5 = X<S>;                // OK
+\end{codeblock}
+\end{example}
+
 \pnum
 When the \grammarterm{template-name}
 of a \grammarterm{simple-template-id}
@@ -7026,30 +7065,11 @@
 \end{example}
 
 \pnum
-When an explicit template argument list is specified, if the template
-arguments are not compatible with the template parameter list or do
-not result in a valid function type as described below, type
-deduction fails.  Specifically, the following steps are performed when
-evaluating an explicitly specified template argument list with respect
-to a given function template:
-\begin{itemize}
-\item If the specified template arguments do not match the template
-parameters in
-kind (i.e., type, non-type, template), or if there
-are more arguments than there are parameters
-and no parameter is a template parameter pack, or if there is not
-an argument for each non-pack parameter,
-type deduction fails.
-
-\item If any non-type argument does not match the type of the
-corresponding non-type
-template parameter, and is not convertible to the type of the
-corresponding non-type parameter as specified in~\ref{temp.arg.nontype},
+When an explicit template argument list is specified, if the
+given \grammarterm{template-id} is invalid\iref{temp.names},
 type deduction fails.
-
-\item The specified template argument values are substituted for the
+The specified template argument values are substituted for the
 corresponding template parameters as specified below.
-\end{itemize}
 
 \pnum
 After this substitution is performed, the function parameter type