c++: using-enum and access specifiers [PR100862]

When copying the enumerators imported by a class-scope using-enum
declaration, we need to override current_access_specifier so that
finish_member_declaration gives the copies the same access as the
using-enum decl.  (A class-scope using-enum is processed late, so
current_access_specifier at this point is otherwise set to the last
access specifier within the class.)  To that end, this patch makes
handle_using_decl call set_current_access_from_decl accordingly.

For consistency, this patch makes build_enumerator use
set_current_access_from_decl too.

	PR c++/100862

gcc/cp/ChangeLog:

	* pt.c (set_current_access_from_decl): Move to ...
	* class.c (set_current_access_from_decl): ... here.
	(handle_using_decl): Use it to propagate the access of the
	using-enum decl to the copy of the imported enumerator.
	* cp-tree.h (set_current_access_from_decl): Declare.
	* decl.c (build_enumerator): Simplify using make_temp_override
	and set_current_access_from_decl.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/using-enum-9.C: New test.

5 files changed, 46 insertions, 24 deletions

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index 354addd..b53a4db 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -207,6 +207,19 @@ static bool type_maybe_constexpr_default_constructor (tree);
 static bool type_maybe_constexpr_destructor (tree);
 static bool field_poverlapping_p (tree);
 
+/* Set CURRENT_ACCESS_SPECIFIER based on the protection of DECL.  */
+
+void
+set_current_access_from_decl (tree decl)
+{
+  if (TREE_PRIVATE (decl))
+    current_access_specifier = access_private_node;
+  else if (TREE_PROTECTED (decl))
+    current_access_specifier = access_protected_node;
+  else
+    current_access_specifier = access_public_node;
+}
+
 /* Return a COND_EXPR that executes TRUE_STMT if this execution of the
    'structor is in charge of 'structing virtual bases, or FALSE_STMT
    otherwise.  */
@@ -1359,6 +1372,8 @@ handle_using_decl (tree using_decl, tree t)
 	 CONST_DECL_USING_P is true.  */
       gcc_assert (TREE_CODE (decl) == CONST_DECL);
 
+      auto cas = make_temp_override (current_access_specifier);
+      set_current_access_from_decl (using_decl);
       tree copy = copy_decl (decl);
       DECL_CONTEXT (copy) = t;
       DECL_ARTIFICIAL (copy) = true;
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index c95a820..b1b7e61 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8186,6 +8186,7 @@ struct atom_hasher : default_hash_traits<tree>
 extern bool subsumes                            (tree, tree);
 
 /* In class.c */
+extern void set_current_access_from_decl (tree);
 extern void cp_finish_injected_record_type (tree);
 
 /* in vtable-class-hierarchy.c */
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index e7268d5..fb21a3a 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -16333,17 +16333,9 @@ incremented enumerator value is too large for %<long%>"));
 
 	 For which case we need to make sure that the access of `S::i'
 	 matches the access of `S::E'.  */
-      tree saved_cas = current_access_specifier;
-      if (TREE_PRIVATE (TYPE_NAME (enumtype)))
-	current_access_specifier = access_private_node;
-      else if (TREE_PROTECTED (TYPE_NAME (enumtype)))
-	current_access_specifier = access_protected_node;
-      else
-	current_access_specifier = access_public_node;
-
+      auto cas = make_temp_override (current_access_specifier);
+      set_current_access_from_decl (TYPE_NAME (enumtype));
       finish_member_declaration (decl);
-
-      current_access_specifier = saved_cas;
     }
   else
     pushdecl (decl);
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 15ef488..7211bdc 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -190,7 +190,6 @@ static tree tsubst_arg_types (tree, tree, tree, tsubst_flags_t, tree);
 static tree tsubst_function_type (tree, tree, tsubst_flags_t, tree);
 static bool check_specialization_scope (void);
 static tree process_partial_specialization (tree);
-static void set_current_access_from_decl (tree);
 static enum template_base_result get_template_base (tree, tree, tree, tree,
 						    bool , tree *);
 static tree try_class_unification (tree, tree, tree, tree, bool);
@@ -26432,19 +26431,6 @@ tsubst_initializer_list (tree t, tree argvec)
   return inits;
 }
 
-/* Set CURRENT_ACCESS_SPECIFIER based on the protection of DECL.  */
-
-static void
-set_current_access_from_decl (tree decl)
-{
-  if (TREE_PRIVATE (decl))
-    current_access_specifier = access_private_node;
-  else if (TREE_PROTECTED (decl))
-    current_access_specifier = access_protected_node;
-  else
-    current_access_specifier = access_public_node;
-}
-
 /* Instantiate an enumerated type.  TAG is the template type, NEWTAG
    is the instantiation (which should have been created with
    start_enum) and ARGS are the template arguments to use.  */
diff --git a/gcc/testsuite/g++.dg/cpp2a/using-enum-9.C b/gcc/testsuite/g++.dg/cpp2a/using-enum-9.C
new file mode 100644
index 0000000..3e02605
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/using-enum-9.C
@@ -0,0 +1,28 @@
+// PR c++/100862
+// { dg-do compile { target c++20 } }
+
+enum class fruit { orange, apple };
+
+struct A {
+public:
+  using enum fruit;
+private:
+};
+
+struct B {
+protected:
+  using enum fruit;
+public:
+};
+
+struct C {
+private:
+  using enum fruit;
+public:
+};
+
+int main() {
+  A::orange, A::apple;
+  B::orange, B::apple; // { dg-error "protected" }
+  C::orange, C::apple; // { dg-error "private" }
+}