[gcc r14-10656] c++: c->B::m access resolved through current inst [PR116320]

[Patrick Palka]

https://gcc.gnu.org/g:149d87fbe661da29d8a0aa671b42bd532206a8b8

commit r14-10656-g149d87fbe661da29d8a0aa671b42bd532206a8b8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Aug 15 10:23:54 2024 -0400

    c++: c->B::m access resolved through current inst [PR116320]
    
    Here when checking the access of (the injected-class-name) B in c->B::m
    at parse time, we notice its context B (now the type) is a base of the
    object type C<T>, so we proceed to use C<T> as the effective qualifying
    type.  But this C<T> is the dependent specialization not the primary
    template type, so it has empty TYPE_BINFO, which leads to a segfault later
    from perform_or_defer_access_check.
    
    The reason the DERIVED_FROM_P (B, C<T>) test guarding this code path works
    despite C<T> having empty TYPE_BINFO is because of its currently_open_class
    logic (added in r9-713-gd9338471b91bbe) which replaces a dependent
    specialization with the primary template type if we're inside it.  So the
    safest fix seems to be to call currently_open_class in the caller as well.
    
            PR c++/116320
    
    gcc/cp/ChangeLog:
    
            * semantics.cc (check_accessibility_of_qualified_id): Try
            currently_open_class when using the object type as the
            effective qualifying type.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/template/access42.C: New test.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>
    (cherry picked from commit 484f139ccd3b631a777802e810a632678b42ffab)

Diff:
---
 gcc/cp/semantics.cc                      | 11 ++++++++---
 gcc/testsuite/g++.dg/template/access42.C | 17 +++++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index b5569066708e..ceeac82fa081 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -2497,9 +2497,14 @@ check_accessibility_of_qualified_id (tree decl,
 	 OBJECT_TYPE.  */
       && CLASS_TYPE_P (object_type)
       && DERIVED_FROM_P (scope, object_type))
-    /* If we are processing a `->' or `.' expression, use the type of the
-       left-hand side.  */
-    qualifying_type = object_type;
+    {
+      /* If we are processing a `->' or `.' expression, use the type of the
+	 left-hand side.  */
+      if (tree open = currently_open_class (object_type))
+	qualifying_type = open;
+      else
+	qualifying_type = object_type;
+    }
   else if (nested_name_specifier)
     {
       /* If the reference is to a non-static member of the
diff --git a/gcc/testsuite/g++.dg/template/access42.C b/gcc/testsuite/g++.dg/template/access42.C
new file mode 100644
index 000000000000..f1dcbce80c24
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/access42.C
@@ -0,0 +1,17 @@
+// PR c++/116320
+// { dg-do compile { target c++11 } }
+
+template<class T> struct C;
+template<class T> using C_ptr = C<T>*;
+
+struct B { int m; using B_typedef = B; };
+
+template<class T>
+struct C : B {
+  void f(C_ptr<T> c) {
+    c->B::m;
+    c->B_typedef::m;
+  }
+};
+
+template struct C<int>;