Re: [PATCH] c++: make __reference_*_from_temporary honor access [PR120529]

[Jason Merrill]

On 11/21/25 4:19 AM, Marek Polacek wrote:

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

-- >8 --
This PR reports that our __reference_*_from_temporary ignore access
control.  The reason is that we only check if implicit_conversion
works, but not if the conversion can actually be performed, via
convert_like.

        PR c++/120529

gcc/cp/ChangeLog:

        * call.cc (ref_conv_binds_to_temporary): Don't ignore access control.

gcc/testsuite/ChangeLog:

        * g++.dg/ext/reference_xes_from_temporary1.C: New test.
---
  gcc/cp/call.cc                                | 16 ++++++++---
  .../ext/reference_xes_from_temporary1.C       | 28 +++++++++++++++++++
  2 files changed, 40 insertions(+), 4 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/ext/reference_xes_from_temporary1.C

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index f80d597b339..ea89130572b 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -10203,11 +10203,19 @@ ref_conv_binds_to_temporary (tree type, tree expr, 
bool direct_init_p/*=false*/)
    const int flags = direct_init_p ? LOOKUP_NORMAL : LOOKUP_IMPLICIT;
    conversion *conv = implicit_conversion (type, TREE_TYPE (expr), expr,
                                          /*c_cast_p=*/false, flags, tf_none);
-  tristate ret (tristate::TS_UNKNOWN);
-  if (conv && !conv->bad_p)
-    ret = tristate (conv_binds_ref_to_temporary (conv));
+  if (!conv || conv->bad_p)
+    return tristate::unknown ();

- return ret;

+  if (conv_binds_ref_to_temporary (conv))
+    {
+      /* Actually perform the conversion to check access control.  */
+      if (convert_like (conv, expr, tf_none) != error_mark_node)
+       return tristate (true);
+      else
+       return tristate::unknown ();
+    }
+
+  return tristate (false);
  }

/* Call the trivial destructor for INSTANCE, which can be either an lvalue of

diff --git a/gcc/testsuite/g++.dg/ext/reference_xes_from_temporary1.C 
b/gcc/testsuite/g++.dg/ext/reference_xes_from_temporary1.C
new file mode 100644
index 00000000000..274de05e7b7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/reference_xes_from_temporary1.C
@@ -0,0 +1,28 @@
+// PR c++/120529
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+class Dst {};
+
+class Src {
+private:
+    operator Dst() const;
+};
+
+class Src2 {
+protected:
+    operator Dst() const;
+};
+
+class Src3 {
+public:
+    operator Dst() const;
+};
+
+SA (!__reference_converts_from_temporary (Dst&&, Src));
+SA (!__reference_constructs_from_temporary (Dst&&, Src));
+SA (!__reference_converts_from_temporary (Dst&&, Src2));
+SA (!__reference_constructs_from_temporary (Dst&&, Src2));
+SA (__reference_converts_from_temporary (Dst&&, Src3));
+SA (__reference_constructs_from_temporary (Dst&&, Src3));

base-commit: b3b2da1389be9f54f72d8933c4eaee972c39de16