c++: Handle auto(x) in parameter-declaration-clause [PR103401]

In C++23, auto(x) is valid, so decltype(auto(x)) should also be valid,
so

  void f(decltype(auto(0)));

should be just as

  void f(int);

but currently, everytime we see 'auto' in a parameter-declaration-clause,
we try to synthesize_implicit_template_parm for it, creating a new template
parameter list.  The code above actually has us calling s_i_t_p twice;
once from cp_parser_decltype_expr -> cp_parser_postfix_expression which
fails and then again from cp_parser_decltype_expr -> cp_parser_expression.
So it looks like we have f<auto, auto> and we accept ill-formed code.

This shows that we need to be more careful about synthesizing the
implicit template parameter.  [dcl.spec.auto.general] says that "A
placeholder-type-specifier of the form type-constraintopt auto can be
used as a decl-specifier of the decl-specifier-seq of a
parameter-declaration of a function declaration or lambda-expression..."
so this patch turns off auto_is_... after we've parsed the decl-specifier-seq.

That doesn't quite cut it yet though, because we also need to handle an
auto nested in the decl-specifier:

  void f(decltype(new auto{0}));

therefore the cp_parser_decltype change.

To accept "sizeof(auto{10})", the cp_parser_type_id_1 hunk only gives a
hard error when we're not parsing tentatively.

The cp_parser_parameter_declaration hunk broke lambda-generic-85713-2.C but
I think the error we issue with this patch is in fact correct, and clang++
agrees.

The r11-1913 change is OK: we need to make sure that we see '(auto)' after
decltype to go ahead with 'decltype(auto)'.

	PR c++/103401

gcc/cp/ChangeLog:

	* parser.c (cp_parser_decltype): Clear
	auto_is_implicit_function_template_parm_p.
	(cp_parser_type_id_1): Give errors only when !cp_parser_simulate_error.
	(cp_parser_parameter_declaration): Clear
	auto_is_implicit_function_template_parm_p after parsing the
	decl-specifier-seq.
	(cp_parser_sizeof_operand): Clear
	auto_is_implicit_function_template_parm_p.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/lambda-generic-85713-2.C: Add dg-error.
	* g++.dg/cpp1y/pr60054.C: Adjust dg-error.
	* g++.dg/cpp1y/pr60332.C: Likewise.
	* g++.dg/cpp2a/concepts-pr84979-2.C: Likewise.
	* g++.dg/cpp2a/concepts-pr84979-3.C: Likewise.
	* g++.dg/cpp2a/concepts-pr84979.C: Likewise.
	* g++.dg/cpp23/auto-fncast7.C: New test.
	* g++.dg/cpp23/auto-fncast8.C: New test.
	* g++.dg/cpp23/auto-fncast9.C: New test.
This commit is contained in:
Marek Polacek 2021-11-25 09:08:03 -05:00
parent 2766448c5c
commit 6a071b2d40
10 changed files with 116 additions and 25 deletions

View File

@ -16432,6 +16432,16 @@ cp_parser_decltype (cp_parser *parser)
= parser->greater_than_is_operator_p;
parser->greater_than_is_operator_p = true;
/* Don't synthesize an implicit template type parameter here. This
could happen with C++23 code like
void f(decltype(new auto{0}));
where we want to deduce the auto right away so that the parameter
is of type 'int *'. */
auto cleanup = make_temp_override
(parser->auto_is_implicit_function_template_parm_p, false);
/* Do not actually evaluate the expression. */
++cp_unevaluated_operand;
@ -24144,22 +24154,22 @@ cp_parser_type_id_1 (cp_parser *parser, cp_parser_flags flags,
/* OK */;
else
{
location_t loc = type_specifier_seq.locations[ds_type_spec];
if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
if (!cp_parser_simulate_error (parser))
{
if (!cp_parser_simulate_error (parser))
location_t loc = type_specifier_seq.locations[ds_type_spec];
if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
{
error_at (loc, "missing template arguments after %qT",
auto_node);
inform (DECL_SOURCE_LOCATION (tmpl), "%qD declared here",
tmpl);
}
else if (parser->in_template_argument_list_p)
error_at (loc, "%qT not permitted in template argument",
auto_node);
else
error_at (loc, "invalid use of %qT", auto_node);
}
else if (parser->in_template_argument_list_p)
error_at (loc, "%qT not permitted in template argument",
auto_node);
else
error_at (loc, "invalid use of %qT", auto_node);
return error_mark_node;
}
}
@ -24668,6 +24678,15 @@ cp_parser_parameter_declaration (cp_parser *parser,
&decl_specifiers,
&declares_class_or_enum);
/* [dcl.spec.auto.general]: "A placeholder-type-specifier of the form
type-constraint opt auto can be used as a decl-specifier of the
decl-specifier-seq of a parameter-declaration of a function declaration
or lambda-expression..." but we must not synthesize an implicit template
type parameter in its declarator. That is, in "void f(auto[auto{10}]);"
we want to synthesize only the first auto. */
auto cleanup = make_temp_override
(parser->auto_is_implicit_function_template_parm_p, false);
/* Complain about missing 'typename' or other invalid type names. */
if (!decl_specifiers.any_type_specifiers_p
&& cp_parser_parse_and_diagnose_invalid_type_name (parser))
@ -32369,6 +32388,9 @@ cp_parser_sizeof_operand (cp_parser* parser, enum rid keyword)
= parser->non_integral_constant_expression_p;
parser->integral_constant_expression_p = false;
auto cleanup = make_temp_override
(parser->auto_is_implicit_function_template_parm_p, false);
/* Do not actually evaluate the expression. */
++cp_unevaluated_operand;
++c_inhibit_evaluation_warnings;

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@ -2,6 +2,6 @@
// { dg-do compile { target c++14 } }
auto l4 = [](auto v, auto (&array (int)) [5]) -> int { return v + array[0]; };
auto l5 = [](auto v, auto (&array (auto)) [5]) -> int { return v + array[0]; };
auto l5 = [](auto v, auto (&array (auto)) [5]) -> int { return v + array[0]; }; // { dg-error ".auto. parameter not permitted in this context" }
auto l6 = [](auto v, auto (&array (int int)) [5]) -> int { return v + array[0]; }; // { dg-error "two or more data types" }
auto l7 = [](auto v, auto (&array (int auto)) [5]) -> int { return v + array[0]; }; // { dg-error "two or more data types" }

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@ -6,6 +6,6 @@ template<typename T> decltype(T{}) fooB(T);
void bar()
{
fooA((auto*)0); // { dg-error "invalid use" }
fooB((auto*)0); // { dg-error "invalid use" }
fooA((auto*)0); // { dg-error "expected" }
fooB((auto*)0); // { dg-error "expected" }
}

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@ -3,4 +3,5 @@
void foo();
auto f = (auto(*)())(&foo); // { dg-error "invalid" }
auto f = (auto(*)())(&foo); // { dg-error "expected" }
// { dg-error "only available" "" { target c++20_down } .-1 }

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@ -0,0 +1,9 @@
// PR c++/103401
// { dg-do compile { target c++23 } }
void f(decltype(auto(0))) { }
int main()
{
f<int,int>(0); // { dg-error "no matching function" }
}

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@ -0,0 +1,42 @@
// PR c++/103401
// { dg-do compile { target c++23 } }
void f1 (decltype(auto(0)));
void f2 (decltype(auto{0}));
void f3 (int = auto(42));
void f4 (int = auto{42});
void f5 (decltype(auto(0)) = auto(42));
void f6 (auto (x));
void f7 (int[auto(10)]);
void f8 (int[auto{10}]);
void f9 (auto[auto{10}]);
void f10 (auto);
void f11 (int x, decltype(x) y);
void f12 (int[sizeof(auto{10})]);
void f13 (int[sizeof(auto(10))]);
void f14 (int[__extension__ alignof(auto{10})]);
void f15 (int[__extension__ alignof(auto(10))]);
void
g ()
{
int a[2];
f1 (1);
f2 (1);
f3 ();
f3 (1);
f4 ();
f4 (1);
f5 ();
f5 (1);
f6 ('a');
f7 (&a[0]);
f8 (&a[0]);
f9 (&a[0]);
f10 (1);
f11 (1, 2);
f12 (&a[0]);
f13 (&a[0]);
f14 (&a[0]);
f15 (&a[0]);
}

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@ -0,0 +1,17 @@
// PR c++/103401
// { dg-do compile { target c++23 } }
void f1(decltype(new auto{0}));
void f2(decltype(new int{0}));
void
g ()
{
int i;
void f3(decltype(new auto{0}));
void f4(decltype(new int{0}));
f1 (&i);
f2 (&i);
f3 (&i);
f4 (&i);
}

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@ -4,9 +4,9 @@
template <typename T>
void foo1(T& t) {
typename T::template C<void> tcv = t;
typename T::template C<auto> u = tcv; // { dg-error "not permitted" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "incomplete|not permitted" }
(typename T::template D<auto> (t)); // { dg-error "invalid|not permitted|unable" }
typename T::template C<auto> u = tcv; // { dg-error "" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "" }
(typename T::template D<auto> (t)); // { dg-error "" }
// { dg-warning "only available" "" { target c++17_down } .-1 }
}
@ -23,9 +23,9 @@ struct T1 {
template <typename T>
void foo2(T& t) {
typename T::template C<void> tcv = t;
typename T::template C<auto> u = tcv; // { dg-error "not permitted" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "incomplete|not permitted" }
T::template D<auto> (t); // { dg-error "invalid|not permitted" }
typename T::template C<auto> u = tcv; // { dg-error "" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "" }
T::template D<auto> (t); // { dg-error "" }
}
struct T2 {

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@ -8,9 +8,9 @@
template <typename T>
void foo1(T& t) {
typename T::template C<void> tcv = t;
typename T::template C<auto> u = tcv; // { dg-error "not permitted" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "incomplete|not permitted" }
(typename T::template D<auto> (t)); // { dg-error "invalid|not permitted|no class" }
typename T::template C<auto> u = tcv; // { dg-error "" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "" }
(typename T::template D<auto> (t)); // { dg-error "" }
// { dg-warning "only available" "" { target c++17_down } .-1 }
}
@ -27,9 +27,9 @@ struct T1 {
template <typename T>
void foo2(T& t) {
typename T::template C<void> tcv = t;
typename T::template C<auto> u = tcv; // { dg-error "not permitted" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "incomplete|not permitted" }
T::template D<auto> (t); // { dg-error "yields a type|not permitted" }
typename T::template C<auto> u = tcv; // { dg-error "" "" { target c++20 } }
T::template C<auto>::f (tcv, u); // { dg-error "" }
T::template D<auto> (t); // { dg-error "" }
}
struct T2 {

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@ -5,5 +5,5 @@ template<typename> void foo() {}
void bar()
{
foo<auto>(); // { dg-error "not permitted|invalid|no matching function" }
foo<auto>(); // { dg-error "" }
}