Re: [PATCH] c++: Allow -Wvirtual-move-assign to be more easily ignored

[Jason Merrill]

On 5/12/25 5:03 PM, Owen Avery wrote:

Please add a little rationale for the change here, perhaps adapting the 
one from your previous patch.

gcc/cp/ChangeLog:

        * method.cc
        (synthesized_method_walk): Check whether -Wvirtual-move-assign

The (function) should usually go on the same line as the source file.

        is enabled at the location of a base class's move assignment
        operator.

gcc/testsuite/ChangeLog:

        * g++.dg/warn/ignore-virtual-move-assign.C: New test.

Co-authored-by: Jason Merrill <ja...@redhat.com>
Signed-off-by: Owen Avery <powerboat9.ga...@gmail.com>
---
  gcc/cp/method.cc                              |  4 +-
  .../g++.dg/warn/ignore-virtual-move-assign.C  | 45 +++++++++++++++++++
  2 files changed, 48 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/warn/ignore-virtual-move-assign.C

diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 05c19cf0661..092bae27787 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2949,7 +2949,9 @@ synthesized_method_walk (tree ctype, 
special_function_kind sfk, bool const_p,
          && BINFO_VIRTUAL_P (base_binfo)
          && fn && TREE_CODE (fn) == FUNCTION_DECL
          && move_fn_p (fn) && !trivial_fn_p (fn)
-         && vbase_has_user_provided_move_assign (BINFO_TYPE (base_binfo)))
+         && vbase_has_user_provided_move_assign (BINFO_TYPE (base_binfo))
+         && warning_enabled_at (DECL_SOURCE_LOCATION (fn),
+                                OPT_Wvirtual_move_assign))
        warning (OPT_Wvirtual_move_assign,
                 "defaulted move assignment for %qT calls a non-trivial "
                 "move assignment operator for virtual base %qT",
diff --git a/gcc/testsuite/g++.dg/warn/ignore-virtual-move-assign.C 
b/gcc/testsuite/g++.dg/warn/ignore-virtual-move-assign.C
new file mode 100644
index 00000000000..73922e69754
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/ignore-virtual-move-assign.C
@@ -0,0 +1,45 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wvirtual-move-assign -Wattributes" }
+
+#include <utility>
+
+class A
+{
+  int val;
+
+public:
+  explicit A (int val) : val (val) {}
+
+  A (const A &oth) : val (0) {}
+  A &operator= (const A &oth) { return *this; }
+  A (A &&oth) : val (oth.val) { oth.val = 0; }
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wvirtual-move-assign"
+  A &operator= (A &&oth)
+  {
+    val += oth.val;
+    oth.val = 0;
+    return *this;
+  }
+#pragma GCC diagnostic pop
+};
+
+class B : virtual A
+{
+public:
+  B () : A (12) {}
+  B &operator= (B &&) = default;
+};
+
+class C : virtual A
+{
+public:
+  C () : A (12) {}
+};
+
+void
+test_fn ()
+{
+  C x, y;
+  x = std::move (y);
+}