CWG2772 Missing Annex C entry for linkage effects of linkage-specification

Author: burblebee

source/compatibility.tex

@@ -1826,6 +1826,27 @@
 revision of \Cpp{} because \tcode{double} to \tcode{int} is a narrowing
 conversion.
 
+\diffref{dcl.link}
+\change
+Names declared in an anonymous namespace
+changed from external linkage to internal linkage;
+language linkage applies to names with external linkage only.
+\rationale
+Alignment with user expectations.
+\effect
+Valid \CppIII{} code may violate the one-definition rule\iref{basic.def.odr}
+in this revision of \Cpp{}.
+For example:
+\begin{codeblock}
+namespace { extern "C" { extern int x; } }  // \#1, previously external linkage and C language linkage,
+                                            // now internal linkage and \Cpp{} language linkage
+namespace A { extern "C" int x = 42; }      // \#2, external linkage and C language linkage
+int main(void) { return x; }
+\end{codeblock}
+This code is valid in \CppIII{},
+but \tcode{\#2} is not a definition for \tcode{\#1}
+in this revision of \Cpp{}, violating the one-definition rule.
+
 \rSec2[diff.cpp03.class]{\ref{class}: classes}
 
 \diffref{class.default.ctor,class.dtor,class.copy.ctor,class.copy.assign}