Re: [PATCH] c++: Fix lambdas with variadic parameters and static specifier [PR119048]

[Eczbek]

On 9/19/25 8:51 AM, Jason Merrill wrote:
On 9/18/25 9:57 PM, Patrick Palka wrote:
On Mon, 15 Sep 2025, Eczbek wrote:
 From d70ac2b0a7b524829d22b3bb6bacbe1ef381c7fb Mon Sep 17 00:00:00 2001
From: Eczbek <eczbek.v...@gmail.com>
Date: Mon, 15 Sep 2025 19:37:20 -0400
Subject: [PATCH] c++: Fix lambdas with variadic parameters and static
  specifier [PR119048]

    PR c++/119048

gcc/cp/ChangeLog:

    * lambda.cc (compare_lambda_sig): Only skip first parameter for
    object members.

gcc/testsuite/ChangeLog:

    * g++.dg/cpp23/static-operator-call8.C: New test.

Signed-off-by: Eczbek <eczbek.v...@gmail.com>
---
  gcc/cp/lambda.cc                                   | 12 ++++++++----
  gcc/testsuite/g++.dg/cpp23/static-operator-call8.C |  6 ++++++
  2 files changed, 14 insertions(+), 4 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp23/static-operator-call8.C

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index 711e3b7a18e..8950404ae1d 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -1742,10 +1742,14 @@ compare_lambda_sig (tree fn_a, tree fn_b)
        || fn_b == error_mark_node)
      return false;

-  for (tree args_a = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (fn_a))),
-     args_b = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (fn_b)));
-       args_a || args_b;
-       args_a = TREE_CHAIN (args_a), args_b = TREE_CHAIN (args_b))
+  tree args_a = TYPE_ARG_TYPES (TREE_TYPE (fn_a));
+  if (DECL_OBJECT_MEMBER_FUNCTION_P (fn_a))
+      args_a = TREE_CHAIN (args_a);

Thanks for the patch!

This definitely seems like an improvement to the current buggy code, but
I think we really only want to skip implicit object parameters since we
should consider explicit object parameters part of the lambda signature
and thus compare them.  Does checking DECL_IOBJ_MEMBER_FUNCTION_P
instead work?

Or shorten to FUNCTION_FIRST_USER_PARMTYPE (fn_[ab]).

Jason

Thanks!

-- >8 --

From d4613869df103ba461ca268c8a803ad529f479ba Mon Sep 17 00:00:00 2001
From: Eczbek <eczbek.v...@gmail.com>
Date: Sat, 20 Sep 2025 08:58:00 -0400
Subject: [PATCH] c++: Fix lambdas with variadic parameters and static
 specifier [PR119048]

        PR c++/119048

gcc/cp/ChangeLog:

        * lambda.cc (compare_lambda_sig): Only skip first parameter for
        object members.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp23/static-operator-call8.C: New test.

Signed-off-by: Eczbek <eczbek.v...@gmail.com>
---
 gcc/cp/lambda.cc                                   | 4 ++--
 gcc/testsuite/g++.dg/cpp23/static-operator-call8.C | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp23/static-operator-call8.C

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index 711e3b7a18e..bb0aa7d0a02 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -1742,8 +1742,8 @@ compare_lambda_sig (tree fn_a, tree fn_b)
       || fn_b == error_mark_node)
     return false;

-  for (tree args_a = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (fn_a))),
-        args_b = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (fn_b)));
+  for (tree args_a = FUNCTION_FIRST_USER_PARMTYPE (fn_a),
+        args_b = FUNCTION_FIRST_USER_PARMTYPE (fn_b);
        args_a || args_b;
        args_a = TREE_CHAIN (args_a), args_b = TREE_CHAIN (args_b))
     {
diff --git a/gcc/testsuite/g++.dg/cpp23/static-operator-call8.C 
b/gcc/testsuite/g++.dg/cpp23/static-operator-call8.C
new file mode 100644
index 00000000000..46aa6b42ce8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/static-operator-call8.C
@@ -0,0 +1,6 @@
+// PR c++/119048
+// { dg-do compile { target c++23 } }
+
+int main() {
+       [] {}, [](...) static {};
+}
--
2.51.0