Merge 2018-06 CWG Motion 1

Fixes #2113

Author: zygoloid

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
@@ -4156,7 +4156,7 @@
 one is a standard-layout class object and
 the other is the first non-static data member of that object, or,
 if the object has no non-static data members,
-the first base class subobject of that object\iref{class.mem}, or
+any base class subobject of that object\iref{class.mem}, or
 \item
 there exists an object \placeholder{c} such that
 \placeholder{a} and \placeholder{c} are pointer-interconvertible, and

source/classes.tex

@@ -801,10 +801,12 @@
 
 \pnum
 If a standard-layout class object has any non-static data members, its address
-is the same as the address of its first non-static data member. Otherwise, its
-address is the same as the address of its first base class subobject (if any).
+is the same as the address of its first non-static data member
+if that member is not a bit-field. Its
+address is also the same as the address of each of its base class subobjects.
 \begin{note}
-There might therefore be unnamed padding within a standard-layout struct object, but
+There might therefore be unnamed padding within a standard-layout struct object
+inserted by an implementation, but
 not at its beginning, as necessary to achieve appropriate alignment.
 \end{note}
 \begin{note}

source/declarators.tex

@@ -2315,7 +2315,10 @@
 and
 the number of elements in
 the \grammarterm{identifier-list} shall be equal to the value of that
-expression. The \grammarterm{unqualified-id} \tcode{get} is looked up
+expression.
+Let \tcode{i} be an index prvalue of type \tcode{std::size_t}
+corresponding to $\tcode{v}_\tcode{i}$.
+The \grammarterm{unqualified-id} \tcode{get} is looked up
 in the scope of \tcode{E} by class member access lookup\iref{basic.lookup.classref},
 and if that finds at least one declaration
 that is a function template whose first template parameter

source/expressions.tex

@@ -5431,10 +5431,14 @@
 
 \begin{itemize}
 \item if \tcode{T1} and \tcode{T2} are the same class type
-(ignoring cv-qualification), or one is a base class of the other, and
+(ignoring cv-qualification) and
 \tcode{T2} is at least as cv-qualified as \tcode{T1},
 the target type is \tcode{T2},
 
+\item otherwise, if \tcode{T2} is a base class of \tcode{T1},
+the target type is \cvqual{cv1} \tcode{T2}, where \cvqual{cv1}
+denotes the cv-qualifiers of \tcode{T1},
+
 \item otherwise, the target type is the type that \tcode{E2} would have
 after applying the
 lvalue-to-rvalue\iref{conv.lval},

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}
@@ -5092,6 +5131,13 @@
 declared with a type
 that contains a placeholder type\iref{dcl.spec.auto},
 
+\item
+an
+\grammarterm{identifier}
+associated by name lookup with
+a variable declared with a type that contains a placeholder type\iref{dcl.spec.auto}
+where the initializer is type-dependent,
+
 \item
 an \grammarterm{identifier} associated by name lookup with one or more
 declarations of member functions of the current instantiation declared
@@ -7026,30 +7072,11 @@
 \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 not valid\iref{temp.names},
 type deduction fails.
-
-\item The specified template argument values are substituted for the
+Otherwise, 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
@@ -7146,6 +7173,9 @@
 inside \tcode{sizeof}, \tcode{decltype}, and other contexts that allow non-constant
 expressions. The substitution proceeds in lexical order and stops when
 a condition that causes deduction to fail is encountered.
+If substitution into different declarations of the same function template would
+cause template instantiations to occur in a different order or not at all,
+the program is ill-formed; no diagnostic required.
 \begin{note}
 The equivalent substitution in exception specifications is
 done only when the \grammarterm{noexcept-specifier} is instantiated,
@@ -7159,10 +7189,14 @@
 template <class T> void f(...) { }
 template <class T> auto g(typename A<T>::X) -> typename T::X;
 template <class T> void g(...) { }
+template <class T> typename T::X h(typename A<T>::X);
+template <class T> auto h(typename A<T>::X) -> typename T::X;   // redeclaration
+template <class T> void h(...) { }
 
-void h() {
+void x() {
   f<int>(0);        // OK, substituting return type causes deduction to fail
   g<int>(0);        // error, substituting parameter type instantiates \tcode{A<int>}
+  h<int>(0);        // ill-formed, no diagnostic required
 }
 \end{codeblock}
 \end{example}