CWG1704 Type checking in explicit instantiation of variable templates

Also fixes CWG1728.

Author: Dawn Perchik

source/templates.tex

@@ -4889,13 +4889,18 @@
 
 \pnum
 If the explicit instantiation is for a class or member class, the
-\grammarterm{elaborated-type-specifier} in the \grammarterm{declaration} shall
-include a \grammarterm{simple-template-id}. If the explicit instantiation is for
+\grammarterm{elaborated-type-specifier} in the \grammarterm{declaration}
+shall include a \grammarterm{simple-template-id};
+otherwise, the \grammarterm{declaration}
+shall be a \grammarterm{simple-declaration} whose \grammarterm{init-declarator-list}
+comprises a single \grammarterm{init-declarator}
+that does not have an \grammarterm{initializer}.
+If the explicit instantiation is for
 a function or member function,
 the
 \grammarterm{unqualified-id}
 in the
-\grammarterm{declaration}
+\grammarterm{declarator}
 shall be either a
 \grammarterm{template-id}
 or, where all template arguments can be deduced, a
@@ -4915,9 +4920,9 @@
 the name of the class template specialization in the
 \grammarterm{qualified-id}
 for the member name shall be a \grammarterm{simple-template-id}.
-If the explicit instantiation is for a variable, the
-\grammarterm{unqualified-id} in the declaration shall be a
-\grammarterm{template-id}.
+If the explicit instantiation is for a variable template specialization,
+the \grammarterm{unqualified-id} in the \grammarterm{declarator}
+shall be a \grammarterm{simple-template-id}.
 An explicit instantiation shall appear in an enclosing namespace
 of its template. If the name declared in the explicit
 instantiation is an unqualified name, the explicit instantiation
@@ -4958,6 +4963,28 @@
 of the explicit instantiation names an implicitly-declared special member
 function (Clause~\ref{special}), the program is ill-formed.
 
+\pnum
+The \grammarterm{declaration} in an \grammarterm{explicit-instantiation} and the \grammarterm{declaration} produced by the corresponding substitution into the templated function, variable, or class are two declarations of the same entity.
+\begin{note}
+These declarations are required to have matching types as specified in~\ref{basic.link}, except as specified in~\ref{except.spec}.
+\begin{example}
+\begin{codeblock}
+template<typename T> T var = {};
+template float var<float>;   // OK, instantiated variable has type \tcode{float}
+template int var<int[16]>[]; // OK, absence of major array bound is permitted
+template int *var<int>;      // error: instantiated variable has type \tcode{int}
+
+template<typename T> auto av = T();
+template int av<int>;        // OK, variable with type \tcode{int} can be redeclared with type \tcode{auto}
+
+template<typename T> auto f() {}
+template void f<int>();      // error: function with deduced return type
+                             // redeclared with non-deduced return type~(\ref{dcl.spec.auto})
+\end{codeblock}
+\end{example}
+\end{note}
+Despite its syntactic form, the \grammarterm{declaration} in an \grammarterm{explicit-instantiation} for a variable is not itself a definition and does not conflict with the definition instantiated by an explicit instantiation definition for that variable.
+
 \pnum
 For a given set of template arguments, if an explicit
 instantiation of a template appears after a declaration of
@@ -5033,8 +5060,9 @@
 literal types,
 variables of reference types, and class template specializations,
 explicit instantiation declarations have the
-effect of suppressing the implicit instantiation of the entity to which they
-refer. \begin{note} The intent is that an inline function that is the
+effect of suppressing the implicit instantiation
+of the definition of the entity to which they refer.
+\begin{note} The intent is that an inline function that is the
 subject of an explicit instantiation declaration will still be implicitly
 instantiated when odr-used~(\ref{basic.def.odr}) so that the body can be considered for inlining, but
 that no out-of-line copy of the inline function would be generated in the