[Modules TS] Module ownership semantics for redeclarations.
When declaring an entity in the "purview" of a module, it's never a
redeclaration of an entity in the purview of a default module or in no module
("in the global module"). Don't consider those other declarations as possible
redeclaration targets if they're not visible, and reject any cases where we
pick a prior visible declaration that violates this rule.
This reinstates r315251 and r315256, reverted in r315309 and r315308
respectively, tweaked to avoid triggering a linkage calculation when declaring
implicit special members (this exposed our pre-existing issue with typedef
names for linkage changing the linkage of types whose linkage has already been
computed and cached in more cases). A testcase for that regression has been
added in r315366.
llvm-svn: 315379
diff --git a/clang/test/Modules/anon-linkage.cpp b/clang/test/Modules/anon-linkage.cpp
new file mode 100644
index 0000000..5906382
--- /dev/null
+++ b/clang/test/Modules/anon-linkage.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++17 -fmodules-ts %s
+
+typedef struct {
+ int c;
+ union {
+ int n;
+ char c[4];
+ } v;
+} mbstate;
+
+export module M;
+export using ::mbstate;