Change the error message from "export declaration can only be used
within a module purview" to "export declaration can only be used within
a module interface" to be technically accurate.
The previous message was misleading because export declarations are
actually within a module purview when used in module implementation
units, but they are only allowed in module interface units.
This addresses the issue pointed out in GitHub issue #149008 where
Bigcheese noted that the diagnostic wording was incorrect.
Fixes#149008
This patch fixes a crash due to following simple program:
> export struct Unit {
> bool operator<(const Unit&);
> };
It would crash since the compiler would set the module ownership for
Unit. And the declaration with a module ownership is assumed to own a
module. But here isn't one. So here is the crash.
This patch fixes this by exiting early if it finds the export decl is
already invalid.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D117093
