c++: Don't constrain template visibility using no-linkage variables [PR122253]

When finding the minimal visibility of a template, any reference to a
dependent automatic variable will cause the instantiation to be marked
as internal linkage.  However, when processing the template decl we
don't yet know whether that should actually be the case, as a given
instantiation may not require referencing the local decl in its
mangling.

This patch fixes the issue by checking for no-linkage decls first, in
which case we just constrain using the type of the entity.  We can't use
a check for lk_external/lk_internal in the other cases, as
instantiations referring to internal types can still have external
linkage as determined by the language, but should still constrain the
visibility of any declarations that refer to them.

	PR c++/122253

gcc/cp/ChangeLog:

	* decl2.cc (min_vis_expr_r): Don't mark no-linkage declarations
	as VISIBILITY_ANON.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/internal-16.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit f062a6b7985fcee82e02b626aada4e0824850bd0)

2 files changed, 36 insertions, 1 deletions

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 63a5a21511d..4a29c4a0b1c 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -2862,7 +2862,12 @@ min_vis_expr_r (tree *tp, int */*walk_subtrees*/, void *data)
 	  break;
 	}
     addressable:
-      if (! TREE_PUBLIC (t))
+      if (decl_linkage (t) == lk_none)
+	tpvis = type_visibility (TREE_TYPE (t));
+      /* Decls that have had their visibility constrained will report
+	 as external linkage, but we still want to transitively constrain
+	 if we refer to them, so just check TREE_PUBLIC instead.  */
+      else if (!TREE_PUBLIC (t))
 	tpvis = VISIBILITY_ANON;
       else
 	tpvis = DECL_VISIBILITY (t);
diff --git a/gcc/testsuite/g++.dg/modules/internal-16.C b/gcc/testsuite/g++.dg/modules/internal-16.C
new file mode 100644
index 00000000000..4a928ae801b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/internal-16.C
@@ -0,0 +1,30 @@
+// PR c++/122253
+// { dg-additional-options "-fmodules -Wtemplate-names-tu-local" }
+
+export module M;
+
+template <int> struct ic {};
+struct S {
+  constexpr operator int() const { return 5; }
+  constexpr int operator&() const { return 8; }
+};
+
+template <typename T> inline void a(T) {
+  T a;
+  static T b;
+  ic<a>{};
+  ic<b>{};
+  ic<&a>{};
+  ic<&b>{};
+}
+
+template <typename T> inline auto b(T x) {
+  return [&](auto y) {
+    return [=](auto z) {
+      return ic<(int)x + (int)&y + (int)z>{};
+    };
+  };
+}
+
+template void a(S);
+ic<5 + 8 + 5> x = b(S{})(S{})(S{});