[gcc r16-3307] c++: pointer to auto member function [PR120757]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:ea6ef13d0fc4e020d8c405333153dad9eee1f18d

commit r16-3307-gea6ef13d0fc4e020d8c405333153dad9eee1f18d
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue Aug 19 23:15:20 2025 -0400

    c++: pointer to auto member function [PR120757]
    
    Here r13-1210 correctly changed &A<int>::foo to not be considered
    type-dependent, but tsubst_expr of the OFFSET_REF got confused trying to
    tsubst a type that involved auto.  Fixed by getting the type from the
    member rather than tsubst.
    
            PR c++/120757
    
    gcc/cp/ChangeLog:
    
            * pt.cc (tsubst_expr) [OFFSET_REF]: Don't tsubst the type.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1y/auto-fn66.C: New test.

Diff:
---
 gcc/cp/pt.cc                           |  8 ++++++--
 gcc/testsuite/g++.dg/cpp1y/auto-fn66.C | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index bb2d0b48fd42..dfabc5437d8b 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22537,12 +22537,16 @@ tsubst_expr (tree t, tree args, tsubst_flags_t 
complain, tree in_decl)
 
     case OFFSET_REF:
       {
-       tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
+       /* We should only get here for an OFFSET_REF like A::m; a .* in a
+          template is represented as a DOTSTAR_EXPR.  */
+       gcc_checking_assert
+         (same_type_p (TREE_TYPE (t), TREE_TYPE (TREE_OPERAND (t, 1))));
        tree op0 = RECUR (TREE_OPERAND (t, 0));
        tree op1 = RECUR (TREE_OPERAND (t, 1));
+       tree type = TREE_TYPE (op1);
        r = build2 (OFFSET_REF, type, op0, op1);
        PTRMEM_OK_P (r) = PTRMEM_OK_P (t);
-       if (!mark_used (TREE_OPERAND (r, 1), complain)
+       if (!mark_used (op1, complain)
            && !(complain & tf_error))
          RETURN (error_mark_node);
        RETURN (r);
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn66.C 
b/gcc/testsuite/g++.dg/cpp1y/auto-fn66.C
new file mode 100644
index 000000000000..413154c2a7f8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn66.C
@@ -0,0 +1,20 @@
+// PR c++/120757
+// { dg-do compile { target c++14 } }
+
+template <typename> struct A
+{
+  auto foo() {}
+};
+
+auto bar(void (A<int>::*)()) {}
+
+template <int> auto baz()
+{
+  bar(&A<int>::foo);
+}
+
+int main()
+{
+  baz<0>();
+  return 0;
+}