c++, v2: Implement C++23 P1169R4 - static operator() [PR106651]

  Hi!

On Sat, Sep 17, 2022 at 01:30:08PM +0200, Jason Merrill wrote:
Below is an updated patch on top of the
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601788.html
patch.

> Ah, OK.  I don't think you need to check for C++23 or CALL_EXPR at all, just
> CONVERSION_RANK of the other candidate conversion.

You mean that for C++20 and earlier without static operator () being
involved it is impossible to see non-standard conversion on the first
argument?
I've instrumented GCC during the weekend to log an cases where
static_1 != static_2 and log also whether the corresponding arg on non-static
has standard-conversion or not and the only cases I saw were with
the standard conversion when this static operator () patch wasn't in,
all similar to:
struct S {
  int foo (long);
  static int foo (long long);
};

void
baz ()
{
  S s;
  s.foo (1);
}
and I can't imagine how there could be something other than standard
conversion for the object on which it is called in those cases.

> And I notice that you have winner = -1 in both cases; the first should be
> winner = 1.

Thanks for noticing that, I actually meant to write winner = -1; in the
first and winner = 1; for the second, but that was only because of
misreading it that -1 is when cand1 is better.

> > > You could use FUNCTION_FIRST_USER_PARM to skip 'this' if present.
> > 
> > Ok, will try.

Done.

> You can use FUNCTION_FIRST_USER_PARMTYPE instead of the ?:.

Done too.

> The reformatting of the next two statements seems unnecessary.

It is unnecessary (and I left it now out), I was just something
that catched my eye that it could be formatted more nicely.

> How about
> 
> void f()
> {
>   auto l = [] (auto x) static { return x; };
>   int (*p)(int) = l;
> }
> 
> ?

You're right.  Except that we ICE on the above for C++14 and 17 in
tsubst_copy_and_build's
20343		else if (identifier_p (templ))
20344		  {
20345		    /* C++20 P0846: we can encounter an IDENTIFIER_NODE here when
20346		       name lookup found nothing when parsing the template name.  */
20347		    gcc_assert (cxx_dialect >= cxx20 || seen_error ());
20348		    RETURN (tid);
20349		  }
and while for C++20 and 23 we don't, we say
error: cannot convert ‘f()::<lambda(auto:1)>’ to ‘int (*)(int)’ in initialization
so I think it is just that the assertion does nothing for C++20/23 and we
didn't manage to look up templ
 <identifier_node 0x7fffea1fdec0 operator() tree_2 simple-op local bindings <0x7fffea3343e8>>

Just as a wild guess, I've tried the attached incremental patch on top of
the inline patch below and both the ICEs and errors are gone, but whether
that is correct or not sadly no idea.

2022-09-19  Jakub Jelinek  <jakub@redhat.com>

	PR c++/106651
gcc/c-family/
	* c-cppbuiltin.cc (c_cpp_builtins): Predefine
	__cpp_static_call_operator=202207L for C++23.
gcc/cp/
	* cp-tree.h (LAMBDA_EXPR_STATIC_P): Implement C++23
	P1169R4 - static operator().  Define.
	* parser.cc (CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR): Document
	that it also allows static.
	(cp_parser_lambda_declarator_opt): Handle static lambda specifier.
	(cp_parser_decl_specifier_seq): Allow RID_STATIC for
	CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR.
	* decl.cc (grok_op_properties): If operator() isn't a method,
	use a different error wording, if it is static member function,
	allow it (for C++20 and older with a pedwarn unless it is
	a lambda function or template instantiation).
	* call.cc (joust): Don't ICE if one candidate is static member
	function and the other is an indirect call.  If the parameter
	conversion on the other candidate is user defined conversion,
	ellipsis or bad conversion, make static member function candidate
	a winner for that parameter. 
	* lambda.cc (maybe_add_lambda_conv_op): Handle static lambdas.
	* error.cc (dump_lambda_function): Print static for static lambdas.
gcc/testsuite/
	* g++.dg/template/error30.C: Adjust expected diagnostics.
	* g++.dg/cpp1z/constexpr-lambda13.C: Likewise.
	* g++.dg/cpp23/feat-cxx2b.C: Test __cpp_static_call_operator.
	* g++.dg/cpp23/static-operator-call1.C: New test.
	* g++.dg/cpp23/static-operator-call2.C: New test.
	* g++.old-deja/g++.jason/operator.C: Adjust expected diagnostics.



	Jakub
2022-09-19  Jakub Jelinek  <jakub@redhat.com>

	* lambda.cc (maybe_add_lambda_conv_op): If !thisarg, for decltype_call
	use callop rather than objfn in prepare_op_call.

	* g++.dg/cpp23/static-operator-call3.C: New test.

--- gcc/cp/lambda.cc.jj	2022-09-19 12:34:46.638522537 +0200
+++ gcc/cp/lambda.cc	2022-09-19 14:19:31.200378854 +0200
@@ -1122,6 +1122,8 @@ maybe_add_lambda_conv_op (tree type)
 	  --nargs;
 	  call = prepare_op_call (objfn, nargs);
 	}
+      else
+	objfn = callop;
 
       if (type_uses_auto (fn_result))
 	decltype_call = prepare_op_call (objfn, nargs);
--- gcc/testsuite/g++.dg/cpp23/static-operator-call3.C.jj	2022-09-19 13:30:27.850765150 +0200
+++ gcc/testsuite/g++.dg/cpp23/static-operator-call3.C	2022-09-19 13:33:04.178620907 +0200
@@ -0,0 +1,10 @@
+// P1169R4 - static operator()
+// { dg-do compile { target c++14 } }
+// { dg-options "" }
+
+void
+foo ()
+{
+  auto a = [] (auto x) static { return x; };					// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } }
+  int (*b) (int) = a;
+}
  

On 9/19/22 08:25, Jakub Jelinek wrote:
> Hi!
> 
> On Sat, Sep 17, 2022 at 01:30:08PM +0200, Jason Merrill wrote:
> Below is an updated patch on top of the
> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601788.html
> patch.
> 
>> Ah, OK.  I don't think you need to check for C++23 or CALL_EXPR at all, just
>> CONVERSION_RANK of the other candidate conversion.
> 
> You mean that for C++20 and earlier without static operator () being
> involved it is impossible to see non-standard conversion on the first
> argument?

I believe so, and even if it were possible the change is correct for 
earlier standards.

> I've instrumented GCC during the weekend to log an cases where
> static_1 != static_2 and log also whether the corresponding arg on non-static
> has standard-conversion or not and the only cases I saw were with
> the standard conversion when this static operator () patch wasn't in,
> all similar to:
> struct S {
>    int foo (long);
>    static int foo (long long);
> };
> 
> void
> baz ()
> {
>    S s;
>    s.foo (1);
> }
> and I can't imagine how there could be something other than standard
> conversion for the object on which it is called in those cases.
> 
>> And I notice that you have winner = -1 in both cases; the first should be
>> winner = 1.
> 
> Thanks for noticing that, I actually meant to write winner = -1; in the
> first and winner = 1; for the second, but that was only because of
> misreading it that -1 is when cand1 is better.
> 
>>>> You could use FUNCTION_FIRST_USER_PARM to skip 'this' if present.
>>>
>>> Ok, will try.
> 
> Done.
> 
>> You can use FUNCTION_FIRST_USER_PARMTYPE instead of the ?:.
> 
> Done too.
> 
>> The reformatting of the next two statements seems unnecessary.
> 
> It is unnecessary (and I left it now out), I was just something
> that catched my eye that it could be formatted more nicely.
> 
>> How about
>>
>> void f()
>> {
>>    auto l = [] (auto x) static { return x; };
>>    int (*p)(int) = l;
>> }
>>
>> ?
> 
> You're right.  Except that we ICE on the above for C++14 and 17 in
> tsubst_copy_and_build's
> 20343		else if (identifier_p (templ))
> 20344		  {
> 20345		    /* C++20 P0846: we can encounter an IDENTIFIER_NODE here when
> 20346		       name lookup found nothing when parsing the template name.  */
> 20347		    gcc_assert (cxx_dialect >= cxx20 || seen_error ());
> 20348		    RETURN (tid);
> 20349		  }
> and while for C++20 and 23 we don't, we say
> error: cannot convert ‘f()::<lambda(auto:1)>’ to ‘int (*)(int)’ in initialization
> so I think it is just that the assertion does nothing for C++20/23 and we
> didn't manage to look up templ
>   <identifier_node 0x7fffea1fdec0 operator() tree_2 simple-op local bindings <0x7fffea3343e8>>
> 
> Just as a wild guess, I've tried the attached incremental patch on top of
> the inline patch below and both the ICEs and errors are gone, but whether
> that is correct or not sadly no idea.

That makes sense.  The patch with followup is OK.

> 2022-09-19  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/106651
> gcc/c-family/
> 	* c-cppbuiltin.cc (c_cpp_builtins): Predefine
> 	__cpp_static_call_operator=202207L for C++23.
> gcc/cp/
> 	* cp-tree.h (LAMBDA_EXPR_STATIC_P): Implement C++23
> 	P1169R4 - static operator().  Define.
> 	* parser.cc (CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR): Document
> 	that it also allows static.
> 	(cp_parser_lambda_declarator_opt): Handle static lambda specifier.
> 	(cp_parser_decl_specifier_seq): Allow RID_STATIC for
> 	CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR.
> 	* decl.cc (grok_op_properties): If operator() isn't a method,
> 	use a different error wording, if it is static member function,
> 	allow it (for C++20 and older with a pedwarn unless it is
> 	a lambda function or template instantiation).
> 	* call.cc (joust): Don't ICE if one candidate is static member
> 	function and the other is an indirect call.  If the parameter
> 	conversion on the other candidate is user defined conversion,
> 	ellipsis or bad conversion, make static member function candidate
> 	a winner for that parameter.
> 	* lambda.cc (maybe_add_lambda_conv_op): Handle static lambdas.
> 	* error.cc (dump_lambda_function): Print static for static lambdas.
> gcc/testsuite/
> 	* g++.dg/template/error30.C: Adjust expected diagnostics.
> 	* g++.dg/cpp1z/constexpr-lambda13.C: Likewise.
> 	* g++.dg/cpp23/feat-cxx2b.C: Test __cpp_static_call_operator.
> 	* g++.dg/cpp23/static-operator-call1.C: New test.
> 	* g++.dg/cpp23/static-operator-call2.C: New test.
> 	* g++.old-deja/g++.jason/operator.C: Adjust expected diagnostics.
> 
> --- gcc/cp/cp-tree.h.jj	2022-09-13 18:57:29.356969560 +0200
> +++ gcc/cp/cp-tree.h	2022-09-19 11:53:19.780594924 +0200
> @@ -504,6 +504,7 @@ extern GTY(()) tree cp_global_trees[CPTI
>         OVL_NESTED_P (in OVERLOAD)
>         DECL_MODULE_EXPORT_P (in _DECL)
>         PACK_EXPANSION_FORCE_EXTRA_ARGS_P (in *_PACK_EXPANSION)
> +      LAMBDA_EXPR_STATIC_P (in LAMBDA_EXPR)
>      4: IDENTIFIER_MARKED (IDENTIFIER_NODEs)
>         TREE_HAS_CONSTRUCTOR (in INDIRECT_REF, SAVE_EXPR, CONSTRUCTOR,
>   	  CALL_EXPR, or FIELD_DECL).
> @@ -1488,6 +1489,10 @@ enum cp_lambda_default_capture_mode_type
>   #define LAMBDA_EXPR_CAPTURE_OPTIMIZED(NODE) \
>     TREE_LANG_FLAG_2 (LAMBDA_EXPR_CHECK (NODE))
>   
> +/* Predicate tracking whether the lambda was declared 'static'.  */
> +#define LAMBDA_EXPR_STATIC_P(NODE) \
> +  TREE_LANG_FLAG_3 (LAMBDA_EXPR_CHECK (NODE))
> +
>   /* True if this TREE_LIST in LAMBDA_EXPR_CAPTURE_LIST is for an explicit
>      capture.  */
>   #define LAMBDA_CAPTURE_EXPLICIT_P(NODE) \
> --- gcc/cp/parser.cc.jj	2022-09-19 11:52:53.140960839 +0200
> +++ gcc/cp/parser.cc	2022-09-19 12:11:15.891823798 +0200
> @@ -1994,7 +1994,7 @@ enum
>        constexpr.  */
>     CP_PARSER_FLAGS_ONLY_TYPE_OR_CONSTEXPR = 0x8,
>     /* When parsing a decl-specifier-seq, only allow mutable, constexpr or
> -     for C++20 consteval.  */
> +     for C++20 consteval or for C++23 static.  */
>     CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR = 0x10,
>     /* When parsing a decl-specifier-seq, allow missing typename.  */
>     CP_PARSER_FLAGS_TYPENAME_OPTIONAL = 0x20,
> @@ -11719,6 +11719,18 @@ cp_parser_lambda_declarator_opt (cp_pars
>         LAMBDA_EXPR_MUTABLE_P (lambda_expr) = 1;
>         quals = TYPE_UNQUALIFIED;
>       }
> +  else if (lambda_specs.storage_class == sc_static)
> +    {
> +      if (LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lambda_expr) != CPLD_NONE
> +	  || LAMBDA_EXPR_CAPTURE_LIST (lambda_expr))
> +	error_at (lambda_specs.locations[ds_storage_class],
> +		  "%<static%> lambda specifier with lambda capture");
> +      else
> +	{
> +	  LAMBDA_EXPR_STATIC_P (lambda_expr) = 1;
> +	  quals = TYPE_UNQUALIFIED;
> +	}
> +    }
>   
>     tx_qual = cp_parser_tx_qualifier_opt (parser);
>     if (omitted_parms_loc && tx_qual)
> @@ -11804,6 +11816,12 @@ cp_parser_lambda_declarator_opt (cp_pars
>       if (lambda_specs.locations[ds_consteval])
>         return_type_specs.locations[ds_consteval]
>   	= lambda_specs.locations[ds_consteval];
> +    if (LAMBDA_EXPR_STATIC_P (lambda_expr))
> +      {
> +	return_type_specs.storage_class = sc_static;
> +	return_type_specs.locations[ds_storage_class]
> +	  = lambda_specs.locations[ds_storage_class];
> +      }
>   
>       p = obstack_alloc (&declarator_obstack, 0);
>   
> @@ -11827,8 +11845,9 @@ cp_parser_lambda_declarator_opt (cp_pars
>         {
>   	DECL_INITIALIZED_IN_CLASS_P (fco) = 1;
>   	DECL_ARTIFICIAL (fco) = 1;
> -	/* Give the object parameter a different name.  */
> -	DECL_NAME (DECL_ARGUMENTS (fco)) = closure_identifier;
> +	if (!LAMBDA_EXPR_STATIC_P (lambda_expr))
> +	  /* Give the object parameter a different name.  */
> +	  DECL_NAME (DECL_ARGUMENTS (fco)) = closure_identifier;
>   	DECL_SET_LAMBDA_FUNCTION (fco, true);
>         }
>       if (template_param_list)
> @@ -16022,8 +16041,15 @@ cp_parser_decl_specifier_seq (cp_parser*
>   	  && token->keyword != RID_MUTABLE
>   	  && token->keyword != RID_CONSTEXPR
>   	  && token->keyword != RID_CONSTEVAL)
> -	error_at (token->location, "%qD invalid in lambda",
> -		  ridpointers[token->keyword]);
> +	{
> +	  if (token->keyword != RID_STATIC)
> +	    error_at (token->location, "%qD invalid in lambda",
> +		      ridpointers[token->keyword]);
> +	  else if (cxx_dialect < cxx23)
> +	    pedwarn (token->location, OPT_Wc__23_extensions,
> +		     "%qD only valid in lambda with %<-std=c++23%> or "
> +		     "%<-std=gnu++23%>", ridpointers[token->keyword]);
> +	}
>   
>         if (ds != ds_last)
>   	set_and_check_decl_spec_loc (decl_specs, ds, token);
> --- gcc/cp/decl.cc.jj	2022-09-19 11:52:53.169960441 +0200
> +++ gcc/cp/decl.cc	2022-09-19 11:53:19.818594402 +0200
> @@ -15294,8 +15294,25 @@ grok_op_properties (tree decl, bool comp
>        an enumeration, or a reference to an enumeration.  13.4.0.6 */
>     if (! methodp || DECL_STATIC_FUNCTION_P (decl))
>       {
> +      if (operator_code == CALL_EXPR)
> +	{
> +	  if (! DECL_STATIC_FUNCTION_P (decl))
> +	    {
> +	      error_at (loc, "%qD must be a member function", decl);
> +	      return false;
> +	    }
> +	  if (cxx_dialect < cxx23
> +	      /* For lambdas we diagnose static lambda specifier elsewhere.  */
> +	      && ! LAMBDA_FUNCTION_P (decl)
> +	      /* For instantiations, we have diagnosed this already.  */
> +	      && ! DECL_USE_TEMPLATE (decl))
> +	    pedwarn (loc, OPT_Wc__23_extensions, "%qD may be a static member "
> +	      "function only with %<-std=c++23%> or %<-std=gnu++23%>", decl);
> +	  /* There are no further restrictions on the arguments to an
> +	     overloaded "operator ()".  */
> +	  return true;
> +	}
>         if (operator_code == TYPE_EXPR
> -	  || operator_code == CALL_EXPR
>   	  || operator_code == COMPONENT_REF
>   	  || operator_code == ARRAY_REF
>   	  || operator_code == NOP_EXPR)
> --- gcc/cp/call.cc.jj	2022-09-13 18:57:10.199226101 +0200
> +++ gcc/cp/call.cc	2022-09-19 13:28:53.511058032 +0200
> @@ -12133,10 +12133,14 @@ joust (struct z_candidate *cand1, struct
>     len = cand1->num_convs;
>     if (len != cand2->num_convs)
>       {
> -      int static_1 = DECL_STATIC_FUNCTION_P (cand1->fn);
> -      int static_2 = DECL_STATIC_FUNCTION_P (cand2->fn);
> +      int static_1 = (TREE_CODE (cand1->fn) == FUNCTION_DECL
> +		      && DECL_STATIC_FUNCTION_P (cand1->fn));
> +      int static_2 = (TREE_CODE (cand2->fn) == FUNCTION_DECL
> +		      && DECL_STATIC_FUNCTION_P (cand2->fn));
>   
> -      if (DECL_CONSTRUCTOR_P (cand1->fn)
> +      if (TREE_CODE (cand1->fn) == FUNCTION_DECL
> +	  && TREE_CODE (cand2->fn) == FUNCTION_DECL
> +	  && DECL_CONSTRUCTOR_P (cand1->fn)
>   	  && is_list_ctor (cand1->fn) != is_list_ctor (cand2->fn))
>   	/* We're comparing a near-match list constructor and a near-match
>   	   non-list constructor.  Just treat them as unordered.  */
> @@ -12145,9 +12149,20 @@ joust (struct z_candidate *cand1, struct
>         gcc_assert (static_1 != static_2);
>   
>         if (static_1)
> -	off2 = 1;
> +	{
> +	  /* C++23 [over.best.ics.general] says:
> +	     When the parameter is the implicit object parameter of a static
> +	     member function, the implicit conversion sequence is a standard
> +	     conversion sequence that is neither better nor worse than any
> +	     other standard conversion sequence.  */
> +	  if (CONVERSION_RANK (cand2->convs[0]) >= cr_user)
> +	    winner = 1;
> +	  off2 = 1;
> +	}
>         else
>   	{
> +	  if (CONVERSION_RANK (cand1->convs[0]) >= cr_user)
> +	    winner = -1;
>   	  off1 = 1;
>   	  --len;
>   	}
> --- gcc/cp/lambda.cc.jj	2022-09-13 18:57:10.267225191 +0200
> +++ gcc/cp/lambda.cc	2022-09-19 12:34:46.638522537 +0200
> @@ -1099,7 +1099,9 @@ maybe_add_lambda_conv_op (tree type)
>     tree optype = TREE_TYPE (callop);
>     tree fn_result = TREE_TYPE (optype);
>   
> -  tree thisarg = build_int_cst (TREE_TYPE (DECL_ARGUMENTS (callop)), 0);
> +  tree thisarg = NULL_TREE;
> +  if (TREE_CODE (optype) == METHOD_TYPE)
> +    thisarg = build_int_cst (TREE_TYPE (DECL_ARGUMENTS (callop)), 0);
>     if (generic_lambda_p)
>       {
>         ++processing_template_decl;
> @@ -1109,18 +1111,22 @@ maybe_add_lambda_conv_op (tree type)
>   	 return expression for a deduced return call op to allow for simple
>   	 implementation of the conversion operator.  */
>   
> -      tree instance = cp_build_fold_indirect_ref (thisarg);
>         tree objfn = lookup_template_function (DECL_NAME (callop),
>   					     DECL_TI_ARGS (callop));
> -      objfn = build_min (COMPONENT_REF, NULL_TREE,
> -			 instance, objfn, NULL_TREE);
> -      int nargs = list_length (DECL_ARGUMENTS (callop)) - 1;
> +      int nargs = list_length (DECL_ARGUMENTS (callop));
> +      if (thisarg)
> +	{
> +	  tree instance = cp_build_fold_indirect_ref (thisarg);
> +	  objfn = build_min (COMPONENT_REF, NULL_TREE,
> +			     instance, objfn, NULL_TREE);
> +	  --nargs;
> +	  call = prepare_op_call (objfn, nargs);
> +	}
>   
> -      call = prepare_op_call (objfn, nargs);
>         if (type_uses_auto (fn_result))
>   	decltype_call = prepare_op_call (objfn, nargs);
>       }
> -  else
> +  else if (thisarg)
>       {
>         direct_argvec = make_tree_vector ();
>         direct_argvec->quick_push (thisarg);
> @@ -1135,9 +1141,11 @@ maybe_add_lambda_conv_op (tree type)
>     tree fn_args = NULL_TREE;
>     {
>       int ix = 0;
> -    tree src = DECL_CHAIN (DECL_ARGUMENTS (callop));
> +    tree src = FUNCTION_FIRST_USER_PARM (callop);
>       tree tgt = NULL;
>   
> +    if (!thisarg && !decltype_call)
> +      src = NULL_TREE;
>       while (src)
>         {
>   	tree new_node = copy_node (src);
> @@ -1160,12 +1168,15 @@ maybe_add_lambda_conv_op (tree type)
>   	if (generic_lambda_p)
>   	  {
>   	    tree a = tgt;
> -	    if (DECL_PACK_P (tgt))
> +	    if (thisarg)
>   	      {
> -		a = make_pack_expansion (a);
> -		PACK_EXPANSION_LOCAL_P (a) = true;
> +		if (DECL_PACK_P (tgt))
> +		  {
> +		    a = make_pack_expansion (a);
> +		    PACK_EXPANSION_LOCAL_P (a) = true;
> +		  }
> +		CALL_EXPR_ARG (call, ix) = a;
>   	      }
> -	    CALL_EXPR_ARG (call, ix) = a;
>   
>   	    if (decltype_call)
>   	      {
> @@ -1193,7 +1204,7 @@ maybe_add_lambda_conv_op (tree type)
>   	     tf_warning_or_error);
>   	}
>       }
> -  else
> +  else if (thisarg)
>       {
>         /* Don't warn on deprecated or unavailable lambda declarations, unless
>   	 the lambda is actually called.  */
> @@ -1203,10 +1214,14 @@ maybe_add_lambda_conv_op (tree type)
>   			   direct_argvec->address ());
>       }
>   
> -  CALL_FROM_THUNK_P (call) = 1;
> -  SET_EXPR_LOCATION (call, UNKNOWN_LOCATION);
> +  if (thisarg)
> +    {
> +      CALL_FROM_THUNK_P (call) = 1;
> +      SET_EXPR_LOCATION (call, UNKNOWN_LOCATION);
> +    }
>   
> -  tree stattype = build_function_type (fn_result, FUNCTION_ARG_CHAIN (callop));
> +  tree stattype
> +    = build_function_type (fn_result, FUNCTION_FIRST_USER_PARMTYPE (callop));
>     stattype = (cp_build_type_attribute_variant
>   	      (stattype, TYPE_ATTRIBUTES (optype)));
>     if (flag_noexcept_type
> @@ -1249,6 +1264,41 @@ maybe_add_lambda_conv_op (tree type)
>   
>     add_method (type, fn, false);
>   
> +  if (thisarg == NULL_TREE)
> +    {
> +      /* For static lambda, just return operator().  */
> +      if (nested)
> +	push_function_context ();
> +      else
> +	/* Still increment function_depth so that we don't GC in the
> +	   middle of an expression.  */
> +	++function_depth;
> +
> +      /* Generate the body of the conversion op.  */
> +
> +      start_preparsed_function (convfn, NULL_TREE,
> +				SF_PRE_PARSED | SF_INCLASS_INLINE);
> +      tree body = begin_function_body ();
> +      tree compound_stmt = begin_compound_stmt (0);
> +
> +      /* decl_needed_p needs to see that it's used.  */
> +      TREE_USED (callop) = 1;
> +      finish_return_stmt (decay_conversion (callop, tf_warning_or_error));
> +
> +      finish_compound_stmt (compound_stmt);
> +      finish_function_body (body);
> +
> +      fn = finish_function (/*inline_p=*/true);
> +      if (!generic_lambda_p)
> +	expand_or_defer_fn (fn);
> +
> +      if (nested)
> +	pop_function_context ();
> +      else
> +	--function_depth;
> +      return;
> +    }
> +
>     /* Generic thunk code fails for varargs; we'll complain in mark_used if
>        the conversion op is used.  */
>     if (varargs_function_p (callop))
> --- gcc/cp/error.cc.jj	2022-09-13 18:57:10.249225432 +0200
> +++ gcc/cp/error.cc	2022-09-19 11:53:19.851593949 +0200
> @@ -1692,7 +1692,13 @@ dump_lambda_function (cxx_pretty_printer
>   {
>     /* A lambda's signature is essentially its "type".  */
>     dump_type (pp, DECL_CONTEXT (fn), flags);
> -  if (!(TYPE_QUALS (class_of_this_parm (TREE_TYPE (fn))) & TYPE_QUAL_CONST))
> +  if (TREE_CODE (TREE_TYPE (fn)) == FUNCTION_TYPE)
> +    {
> +      pp->padding = pp_before;
> +      pp_c_ws_string (pp, "static");
> +    }
> +  else if (!(TYPE_QUALS (class_of_this_parm (TREE_TYPE (fn)))
> +	     & TYPE_QUAL_CONST))
>       {
>         pp->padding = pp_before;
>         pp_c_ws_string (pp, "mutable");
> --- gcc/c-family/c-cppbuiltin.cc.jj	2022-09-13 18:57:10.128227052 +0200
> +++ gcc/c-family/c-cppbuiltin.cc	2022-09-19 11:53:19.873593647 +0200
> @@ -1081,6 +1081,7 @@ c_cpp_builtins (cpp_reader *pfile)
>   	  cpp_define (pfile, "__cpp_constexpr=202110L");
>   	  cpp_define (pfile, "__cpp_multidimensional_subscript=202110L");
>   	  cpp_define (pfile, "__cpp_named_character_escapes=202207L");
> +	  cpp_define (pfile, "__cpp_static_call_operator=202207L");
>   	}
>         if (flag_concepts)
>           {
> --- gcc/testsuite/g++.dg/template/error30.C.jj	2020-07-28 15:39:10.020756063 +0200
> +++ gcc/testsuite/g++.dg/template/error30.C	2022-09-19 11:53:19.880593550 +0200
> @@ -2,4 +2,4 @@
>   
>   template<int> struct A;
>   
> -template<template<typename> class B> A<B<int>::x> operator() (); // { dg-error "51:.A<B<int>::x> operator\\(\\)\\(\\). must be a non-static member function" }
> +template<template<typename> class B> A<B<int>::x> operator() (); // { dg-error "51:.A<B<int>::x> operator\\(\\)\\(\\). must be a member function" }
> --- gcc/testsuite/g++.dg/cpp1z/constexpr-lambda13.C.jj	2020-01-12 11:54:37.127402637 +0100
> +++ gcc/testsuite/g++.dg/cpp1z/constexpr-lambda13.C	2022-09-19 12:47:20.398209828 +0200
> @@ -2,4 +2,4 @@
>   
>   auto l1 = []() constexpr constexpr { }; // { dg-error "duplicate" }
>   auto l2 = []() mutable mutable { }; // { dg-error "duplicate" }
> -auto l3 = []() static { };	    // { dg-error "static" }
> +auto l3 = []() static { };	    // { dg-error "static' only valid in lambda with" "" { target c++20_down } }
> --- gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C.jj	2022-09-13 18:57:10.408223302 +0200
> +++ gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C	2022-09-19 11:53:19.907593180 +0200
> @@ -563,3 +563,9 @@
>   #elif __cpp_named_character_escapes != 202207
>   #  error "__cpp_named_character_escapes != 202207"
>   #endif
> +
> +#ifndef __cpp_static_call_operator
> +#  error "__cpp_static_call_operator"
> +#elif __cpp_static_call_operator != 202207
> +#  error "__cpp_static_call_operator != 202207"
> +#endif
> --- gcc/testsuite/g++.dg/cpp23/static-operator-call1.C.jj	2022-09-19 11:53:19.908593166 +0200
> +++ gcc/testsuite/g++.dg/cpp23/static-operator-call1.C	2022-09-19 13:32:10.095362732 +0200
> @@ -0,0 +1,41 @@
> +// P1169R4 - static operator()
> +// { dg-do compile { target c++11 } }
> +// { dg-options "" }
> +
> +template <typename T>
> +struct S
> +{
> +  static constexpr bool operator () (T const &x, T const &y) { return x < y; }; // { dg-warning "may be a static member function only with" "" { target c++20_down } }
> +  using P = bool (*) (T const &, T const &);
> +  operator P () const { return operator (); }
> +};
> +
> +static_assert (S<int> {} (1, 2), "");
> +
> +template <typename T>
> +void
> +bar (T &x)
> +{
> +  x (1, 2);
> +}
> +
> +void
> +foo ()
> +{
> +#if __cpp_constexpr >= 201603L
> +  auto a = [](int x, int y) static constexpr { return x + y; };			// { dg-warning "'static' only valid in lambda with" "" { target { c++17 && c++20_down } } }
> +  static_assert (a (1, 2) == 3, "");
> +  bar (*a);
> +#endif
> +  auto b = []() static { return 1; };						// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } }
> +  b ();
> +  auto c = [](int x, int y) static { return x + y; };				// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } }
> +  c (1, 2);
> +  bar (*c);
> +#if __cpp_generic_lambdas >= 201707L
> +  auto d = []<typename T, typename U>(T x, U y) static { return x + y; };	// { dg-warning "'static' only valid in lambda with" "" { target c++20_only } }
> +  d (1, 2L);
> +#endif
> +  S<long> s;
> +  s(1L, 2L);
> +}
> --- gcc/testsuite/g++.dg/cpp23/static-operator-call2.C.jj	2022-09-19 11:53:19.908593166 +0200
> +++ gcc/testsuite/g++.dg/cpp23/static-operator-call2.C	2022-09-19 12:54:54.226996543 +0200
> @@ -0,0 +1,22 @@
> +// P1169R4 - static operator()
> +// { dg-do compile { target c++11 } }
> +// { dg-options "" }
> +
> +void
> +foo ()
> +{
> +  int u = 0;
> +  auto a = [](int x, int y) mutable mutable { return x + y; };		// { dg-error "duplicate 'mutable' specifier" }
> +  auto b = [](int x, int y) static static { return x + y; };		// { dg-error "duplicate 'static' specifier" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +  auto c = [](int x, int y) static mutable { return x + y; };		// { dg-error "'mutable' specifier conflicts with 'static'" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +  auto d = [](int x, int y) mutable static { return x + y; };		// { dg-error "'static' specifier conflicts with 'mutable'" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +  auto e = [=](int x, int y) static { return x + y; };			// { dg-error "lambda specifier with lambda capture" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +  auto f = [&](int x, int y) static { return x + y; };			// { dg-error "lambda specifier with lambda capture" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +  auto g = [u](int x, int y) static { return x + y; };			// { dg-error "lambda specifier with lambda capture" }
> +									// { dg-warning "'static' only valid in lambda with" "" { target c++20_down } .-1 }
> +}
> --- gcc/testsuite/g++.old-deja/g++.jason/operator.C.jj	2020-07-28 15:39:10.024756008 +0200
> +++ gcc/testsuite/g++.old-deja/g++.jason/operator.C	2022-09-19 11:53:19.918593029 +0200
> @@ -6,7 +6,7 @@ typedef __SIZE_TYPE__ size_t;
>   
>   struct A {
>     int operator?:(int a, int b);	   // { dg-error "prohibits overloading" }
> -  static int operator()(int a);	   // { dg-error "14:.static int A::operator\\(\\)\\(int\\). must be a non-static member function" }
> +  static int operator()(int a);	   // { dg-warning "14:.static int A::operator\\(\\)\\(int\\). may be a static member function only with" "" { target c++20_down } }
>     static int operator+(A,A);	   // { dg-error "14:.static int A::operator\\+\\(A, A\\). must be either a non-static member function or a non-member function" }
>     int operator+(int a, int b = 1); // { dg-error "7:.int A::operator\\+\\(int, int\\). must have either zero or one argument" }
>     int operator++(char);		   // { dg-error "7:postfix .int A::operator\\+\\+\\(char\\). must have .int. as its argument" }
> 
> 
> 	Jakub