Merge 2019-02 CWG Motion 10

P1009R2 Array size deduction in new-expressions

Fixes #2690.

Author: zygoloid

source/expressions.tex

@@ -4433,7 +4433,7 @@
 
 \begin{bnf}
 \nontermdef{noptr-new-declarator}\br
-    \terminal{[} expression \terminal{]} \opt{attribute-specifier-seq}\br
+    \terminal{[} \opt{expression} \terminal{]} \opt{attribute-specifier-seq}\br
     noptr-new-declarator \terminal{[} constant-expression \terminal{]} \opt{attribute-specifier-seq}
 \end{bnf}
 
@@ -4547,9 +4547,6 @@
 \grammarterm{noptr-new-declarator} shall be a converted constant
 expression\iref{expr.const} of type \tcode{std::size_t} and
 shall evaluate to a strictly positive value.
-\indextext{\idxcode{new}}%
-The \grammarterm{expression} in a \grammarterm{noptr-new-declarator} is
-implicitly converted to \tcode{std::size_t}.
 \begin{example}
 Given the definition \tcode{int n = 42},
 \tcode{new float[n][5]} is well-formed (because \tcode{n} is the
@@ -4559,9 +4556,20 @@
 \end{example}
 
 \pnum
+If the \grammarterm{type-id} or \grammarterm{new-type-id}
+denotes an array type of unknown bound\iref{dcl.array},
+the \grammarterm{new-initializer} shall not be omitted;
+the allocated object is an array with \tcode{n} elements,
+where \tcode{n} is determined from the number of initial elements
+supplied in
+the \grammarterm{new-initializer}~(\ref{dcl.init.aggr}, \ref{dcl.init.string}).
+
+\pnum
+\indextext{\idxcode{new}}%
+If the \grammarterm{expression} in a \grammarterm{noptr-new-declarator}
+is present, it is implicitly converted to \tcode{std::size_t}.
 \indextext{function!allocation}%
-The \grammarterm{expression} in a \grammarterm{noptr-new-declarator} is
-erroneous if:
+The \grammarterm{expression} is erroneous if:
 
 \begin{itemize}
 \item