On Thu, 24 Jul 2025, Jason Merrill wrote:
> Tested x86_64-pc-linux-gnu, applying to trunk.
>
> -- 8< --
>
> The lambda conversion was ICEing for two C++23 features, static op() and
> explicit object parameters. The issue with the former seems like a more
> general issue: tsubst_function_decl recursing to substitute the parameters
> was affected by cp_unevaluated_operand from the decltype that refers to the
> declaration. Various places already make a point of clearing
> cp_unevaluated_operand ahead of PARM_DECL tsubsting; doing it here makes the
> PR101233 fix redundant.
Shall we also partially revert r9-5971-g60378a964a2a6b by moving down
the cp_evaluated in tsubst_lambda_expr to just before tsubsting the body
of the lambda so that it better reflects its comment?
>
> For explicit object lambdas, we want to implement CWG2561 and
> just not declare the conversion.
>
> PR c++/114632
> PR c++/101233
>
> gcc/cp/ChangeLog:
>
> * lambda.cc (maybe_add_lambda_conv_op): Not for xobj lambda.
> * pt.cc (tsubst_function_decl): Add cp_evaluated.
> (alias_ctad_tweaks): Revert PR101233 fix.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp23/explicit-obj-lambda18.C: New test.
> * g++.dg/cpp23/static-operator-call7.C: New test.
> ---
> gcc/cp/lambda.cc | 4 +++-
> gcc/cp/pt.cc | 11 ++++-------
> gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda18.C | 12 ++++++++++++
> gcc/testsuite/g++.dg/cpp23/static-operator-call7.C | 12 ++++++++++++
> 4 files changed, 31 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda18.C
> create mode 100644 gcc/testsuite/g++.dg/cpp23/static-operator-call7.C
>
> diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
> index 525e8ef4b34..ecf55eb94d0 100644
> --- a/gcc/cp/lambda.cc
> +++ b/gcc/cp/lambda.cc
> @@ -1143,7 +1143,9 @@ maybe_add_lambda_conv_op (tree type)
> tree lam = CLASSTYPE_LAMBDA_EXPR (type);
>
> if (LAMBDA_EXPR_CAPTURE_LIST (lam) != NULL_TREE
> - || LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lam) != CPLD_NONE)
> + || LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lam) != CPLD_NONE
> + /* CWG2561 ...and no explicit object parameter. */
> + || DECL_XOBJ_MEMBER_FUNCTION_P (callop))
> return;
>
> if (processing_template_decl)
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index d63fa68058b..8e175337b71 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -14916,6 +14916,9 @@ tsubst_function_decl (tree t, tree args,
> tsubst_flags_t complain,
> argvec = NULL_TREE;
> }
>
> + /* Make sure tsubst_decl substitutes all the parameters. */
> + cp_evaluated ev;
> +
> tree closure = (lambda_fntype ? TYPE_METHOD_BASETYPE (lambda_fntype)
> : NULL_TREE);
> tree ctx = closure ? closure : DECL_CONTEXT (t);
> @@ -31214,14 +31217,8 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
> /* Substitute the deduced arguments plus the rewritten template
> parameters into f to get g. This covers the type, copyness,
> guideness, and explicit-specifier. */
> - tree g;
> - {
> - /* Parms are to have DECL_CHAIN tsubsted, which would be skipped
> - if cp_unevaluated_operand. */
> - cp_evaluated ev;
> - g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain,
> + tree g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain,
> /*use_spec_table=*/false);
> - }
> if (g == error_mark_node)
> continue;
> DECL_NAME (g) = name;
> diff --git a/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda18.C
> b/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda18.C
> new file mode 100644
> index 00000000000..d54a93d1de1
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda18.C
> @@ -0,0 +1,12 @@
> +// PR c++/114632
> +// { dg-do compile { target c++23 } }
> +
> +struct S {};
> +
> +auto lambda = [](this auto& self, const int x) /* -> void */ {};
> +
> +int main()
> +{
> + void (*func)(S&, int) = lambda; // { dg-error "" }
> + return 0;
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp23/static-operator-call7.C
> b/gcc/testsuite/g++.dg/cpp23/static-operator-call7.C
> new file mode 100644
> index 00000000000..7c381e69416
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp23/static-operator-call7.C
> @@ -0,0 +1,12 @@
> +// PR c++/114632
> +// { dg-do compile { target c++23 } }
> +
> +struct S {};
> +
> +auto lambda = [](auto, const int x) static /* -> void */ {};
> +
> +int main()
> +{
> + void (*func)(int, int) = lambda;
> + return 0;
> +}
>
> base-commit: 44e32178031e89399710c3ee7444891631a9c8ec
> --
> 2.50.1
>
>
