Merge 2019-07 CWG Motion 17

P1143R2 Adding the constinit keyword

Fixes #2997.

Author: zygoloid

source/compatibility.tex

@@ -1819,6 +1819,9 @@
 The \tcode{consteval} keyword is added to
 declare immediate functions\iref{dcl.constexpr}.
 \item
+The \keyword{constinit} keyword is added to
+prevent unintended dynamic initialization\iref{dcl.constinit}.
+\item
 The \tcode{co_await}, \tcode{co_yield}, and \tcode{co_return} keywords are added
 to enable the definition of coroutines \iref{dcl.fct.def.coroutine}.
 \item

source/declarations.tex

@@ -257,6 +257,7 @@
     \keyword{typedef}\br
     \keyword{constexpr}\br
     \keyword{consteval}\br
+    \keyword{constinit}\br
     \keyword{inline}
 \end{bnf}
 
@@ -276,8 +277,9 @@
 Each \grammarterm{decl-specifier}
 shall appear at most once in a complete \grammarterm{decl-specifier-seq},
 except that \tcode{long} may appear twice.
-The \tcode{constexpr} and \tcode{consteval} \grammarterm{decl-specifier}{s}
-shall not both appear in a \grammarterm{decl-specifier-seq}.
+At most one of
+the \keyword{constexpr}, \keyword{consteval}, and \keyword{constinit} keywords
+shall appear in a \grammarterm{decl-specifier-seq}.
 
 \pnum
 \indextext{ambiguity!declaration type}%
@@ -1015,6 +1017,35 @@
 \end{codeblock}
 \end{example}
 
+\rSec2[dcl.constinit]{The \tcode{constinit} specifier}
+\indextext{specifier!\idxcode{constinit}}
+
+\pnum
+The \keyword{constinit} specifier shall be applied only
+to a declaration of a variable with static or thread storage duration.
+If the specifier is applied to any declaration of a variable,
+it shall be applied to the initializing declaration.
+No diagnostic is required if no \keyword{constinit} declaration
+is reachable at the point of the initializing declaration.
+
+\pnum
+If a variable declared with the \keyword{constinit} specifier has
+dynamic initialization\iref{basic.start.dynamic}, the program is ill-formed.
+\begin{note}
+The \keyword{constinit} specifier ensures that the variable
+is initialized during static initialization\iref{basic.start.static}.
+\end{note}
+
+\pnum
+\begin{example}
+\begin{codeblock}
+const char * g() { return "dynamic initialization"; }
+constexpr const char * f(bool p) { return p ? "constant initializer" : g(); }
+constinit const char * c = f(true);     // OK
+constinit const char * d = f(false);    // ill-formed
+\end{codeblock}
+\end{example}
+
 \rSec2[dcl.inline]{The \tcode{inline} specifier}%
 \indextext{specifier!\idxcode{inline}}
 

source/lex.tex

@@ -732,8 +732,9 @@
 \keyword{concept} \\
 \keyword{const} \\
 \keyword{consteval} \\
-\columnbreak
 \keyword{constexpr} \\
+\columnbreak
+\keyword{constinit} \\
 \keyword{const_cast} \\
 \keyword{continue} \\
 \keyword{co_await} \\
@@ -749,8 +750,8 @@
 \keyword{enum} \\
 \keyword{explicit} \\
 \keyword{export} \\
-\columnbreak
 \keyword{extern} \\
+\columnbreak
 \keyword{false} \\
 \keyword{float} \\
 \keyword{for} \\
@@ -766,9 +767,9 @@
 \keyword{noexcept} \\
 \keyword{nullptr} \\
 \keyword{operator} \\
-\columnbreak
 \keyword{private} \\
 \keyword{protected} \\
+\columnbreak
 \keyword{public} \\
 \keyword{register} \\
 \keyword{reinterpret_cast} \\
@@ -783,10 +784,10 @@
 \keyword{struct} \\
 \keyword{switch} \\
 \keyword{template} \\
-\columnbreak
 \keyword{this} \\
 \keyword{thread_local} \\
 \keyword{throw} \\
+\columnbreak
 \keyword{true} \\
 \keyword{try} \\
 \keyword{typedef} \\

source/preprocessor.tex

@@ -1685,6 +1685,7 @@
 \defnxname{cpp_char8_t}                           & \tcode{201811L} \\ \rowsep
 \defnxname{cpp_conditional_explicit}              & \tcode{201806L} \\ \rowsep
 \defnxname{cpp_constexpr}                         & \tcode{201907L} \\ \rowsep
+\defnxname{cpp_constinit}                         & \tcode{201907L} \\ \rowsep
 \defnxname{cpp_coroutines}                        & \tcode{201902L} \\ \rowsep
 \defnxname{cpp_decltype}                          & \tcode{200707L} \\ \rowsep
 \defnxname{cpp_decltype_auto}                     & \tcode{201304L} \\ \rowsep