P1811R0 Relaxing redefinition restrictions for re-exportation robustness

Author: jensmaurer

source/basic.tex

@@ -274,9 +274,8 @@
 \rSec1[basic.def.odr]{One-definition rule}
 
 \pnum
-A variable, function, class type, enumeration type, or template
-shall not be defined where a prior definition is necessarily reachable\iref{module.reach};
-no diagnostic is required if the prior declaration is in another translation unit.
+No translation unit shall contain more than one definition of any
+variable, function, class type, enumeration type, or template.
 
 \pnum
 \indextext{expression!potentially evaluated}%
@@ -550,8 +549,7 @@
 specialization for which some template parameters are not
 specified~(\ref{temp.spec}, \ref{temp.class.spec}) in a program
 provided that
-no prior definition is necessarily reachable\iref{module.reach}
-at the point where a definition appears, and
+each definition appears in a different translation unit, and
 provided the definitions satisfy the following requirements.
 There shall not be more than one definition
 of an entity

source/modules.tex

@@ -858,7 +858,7 @@
 \item the point at the end of translation unit \#3, and
 \item the point of the call to \tcode{g(0)},
 \end{itemize}
-so the definition of \tcode{X} is not necessarily reachable,
+so the definition of \tcode{X} need not be reachable,
 as described in \ref{module.reach}.
 \end{example}
 
@@ -897,16 +897,14 @@
 
 \pnum
 A declaration $D$ is
-\defnx{reachable}{reachable!declaration} or
-\defnx{necessarily reachable}{reachable!necessarily!declaration},
-respectively, if,
+\defnx{reachable}{reachable!declaration}, if,
 for any point $P$ in the
 instantiation context\iref{module.context},
 \begin{itemize}
 \item $D$ appears prior to $P$ in the same translation unit, or
 \item $D$ is not discarded\iref{module.global},
 appears in a translation unit that is
-reachable or necessarily reachable from $P$, respectively,
+reachable from $P$,
 and
 either does not appear within a \grammarterm{private-module-fragment}
 or appears in a \grammarterm{private-module-fragment}

source/preprocessor.tex

@@ -621,6 +621,7 @@
 \pnum
 If the header identified by the \grammarterm{header-name}
 denotes an importable header\iref{module.import},
+it is implementation-defined whether
 the preprocessing directive
 is instead replaced by the \grammarterm{preprocessing-token}{s}
 \begin{ncbnf}
@@ -1700,6 +1701,7 @@
 \defnxname{cpp_initializer_lists}                 & \tcode{200806L} \\ \rowsep
 \defnxname{cpp_inline_variables}                  & \tcode{201606L} \\ \rowsep
 \defnxname{cpp_lambdas}                           & \tcode{200907L} \\ \rowsep
+\defnxname{cpp_modules}                           & \tcode{201907L} \\ \rowsep
 \defnxname{cpp_namespace_attributes}              & \tcode{201411L} \\ \rowsep
 \defnxname{cpp_noexcept_function_type}            & \tcode{201510L} \\ \rowsep
 \defnxname{cpp_nontype_template_args}             & \tcode{201411L} \\ \rowsep