[gcc r17-3479] c++: Avoid access check for dependent lookup result [PR124983]

https://gcc.gnu.org/g:151ded854245c1578706a9da4843f17f55de33d0

commit r17-3479-g151ded854245c1578706a9da4843f17f55de33d0
Author: Odysseas Georgoudis <[email protected]>
Date:   Sun Jul 26 23:48:20 2026 +0100

    c++: Avoid access check for dependent lookup result [PR124983]
    
    strip_using_decl turns a dependent typename USING_DECL into a dependent
    TYPE_DECL.  If member lookup finds that declaration while looking for a
    typo correction, lookup_member can therefore try to perform an access
    check on it.  Access checks for dependent declarations need to wait until
    substitution, and enforce_access asserts this invariant.
    
    Skip the access check whenever the lookup result refers to a member of a
    dependent scope, not just when it remains a USING_DECL.
    
    gcc/cp/ChangeLog:
    
            PR c++/124983
            * search.cc (lookup_member): Skip access checks for declarations
            from dependent scope.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/124983
            * g++.dg/template/pr124983.C: New test.
    
    Signed-off-by: Odysseas Georgoudis <[email protected]>
    Co-authored-by: Jason Merrill <[email protected]>

Diff:
---
 gcc/cp/search.cc                         |  7 +++--
 gcc/testsuite/g++.dg/template/pr124983.C | 49 ++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/search.cc b/gcc/cp/search.cc
index a51fd1cd6a75..9845032d28d2 100644
--- a/gcc/cp/search.cc
+++ b/gcc/cp/search.cc
@@ -1280,9 +1280,10 @@ lookup_member (tree xbasetype, tree name, int protect, bool want_type,
     {
       tree decl = is_overloaded_fn (rval) ? get_first_fn (rval) : rval;
       decl = strip_using_decl (decl);
-      /* A dependent USING_DECL will be checked after tsubsting.  */
-      if (TREE_CODE (decl) != USING_DECL
-	  && !DECL_IOBJ_MEMBER_FUNCTION_P (decl)
+      /* A dependent declaration will be checked after tsubsting.  */
+      if (!dependent_scope_p (DECL_CONTEXT (decl))
+	  && !(DECL_DECLARES_FUNCTION_P (decl)
+	       && DECL_IOBJ_MEMBER_FUNCTION_P (decl))
 	  && !perform_or_defer_access_check (basetype_path, decl, decl,
 					     complain, afi))
 	return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/template/pr124983.C b/gcc/testsuite/g++.dg/template/pr124983.C
new file mode 100644
index 000000000000..72819af48c0e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr124983.C
@@ -0,0 +1,49 @@
+// PR c++/124983
+// { dg-do compile }
+
+template <class T>
+struct A
+{
+  using typename T::Type;
+
+  void f()
+  {
+    this->type(); // { dg-error "no member named 'type'; did you mean 'Type'" }
+  }
+};
+
+template <class T>
+struct B
+{
+  typedef typename T::Type Type;
+  static T Value;
+
+  void f()
+  {
+    this->type(); // { dg-error "no member named 'type'; did you mean 'Type'" }
+    this->value(); // { dg-error "no member named 'value'; did you mean 'Value'" }
+  }
+};
+
+struct X
+{
+  typedef int Type;
+};
+
+template <class T>
+struct C
+{
+private:
+  typedef typename T::Type Type; // { dg-message "declared private" }
+  static T Value; // { dg-message "declared private" }
+};
+
+template <class T>
+void g()
+{
+  typename C<T>::Type t; // { dg-error "private within this context" }
+  (void) C<T>::Value; // { dg-error "private within this context" }
+  (void) t;
+}
+
+template void g<X>(); // { dg-message "required from here" }