Message ID | 20211201151614.1497902-1-polacek@redhat.com |
---|---|
State | New |
Headers | show |
Series | c++: Handle auto(x) in parameter-declaration-clause [PR103401] | expand |
On 12/1/21 10:16, Marek Polacek wrote: > 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. > > So we need to be more careful about synthesizing the implicit template > parameter. cp_parser_postfix_expression looked like a sensible place. Does this cover other uses of auto in decltype, such as void f(decltype(new auto{0})); ? Should we adjust this flag in cp_parser_decltype along with all the other flags? > The r11-1913 change is OK: we need to make sure that we see '(auto)' after > decltype to go ahead with 'decltype(auto)'. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > PR c++/103401 > > gcc/cp/ChangeLog: > > * parser.c (cp_parser_postfix_expression): Set > auto_is_implicit_function_template_parm_p when parsing a postfix > expression. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp23/auto-fncast7.C: New test. > * g++.dg/cpp23/auto-fncast8.C: New test. > --- > gcc/cp/parser.c | 2 ++ > gcc/testsuite/g++.dg/cpp23/auto-fncast7.C | 9 ++++++++ > gcc/testsuite/g++.dg/cpp23/auto-fncast8.C | 28 +++++++++++++++++++++++ > 3 files changed, 39 insertions(+) > create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast7.C > create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast8.C > > diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c > index 55e6a1a8b3a..c43b180f888 100644 > --- a/gcc/cp/parser.c > +++ b/gcc/cp/parser.c > @@ -7508,6 +7508,8 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p, > looking at a functional cast. We could also be looking at > an id-expression. So, we try the functional cast, and if > that doesn't work we fall back to the primary-expression. */ > + auto cleanup = make_temp_override > + (parser->auto_is_implicit_function_template_parm_p, false); > cp_parser_parse_tentatively (parser); > /* Look for the simple-type-specifier. */ > ++parser->prevent_constrained_type_specifiers; > diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C > new file mode 100644 > index 00000000000..763164f3e5b > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C > @@ -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" } > +} > diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C > new file mode 100644 > index 00000000000..760827a5d6e > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C > @@ -0,0 +1,28 @@ > +// 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 > +g () > +{ > + f1 (1); > + f2 (1); > + f3 (); > + f3 (1); > + f4 (); > + f4 (1); > + f5 (); > + f5 (1); > + f6 ('a'); > + int a[10]; > + f7 (&a[0]); > + f8 (&a[0]); > +} > > base-commit: e5440bc08e07fd491dcccd47e1b86a5985ee117c >
On Wed, Dec 01, 2021 at 11:24:58PM -0500, Jason Merrill wrote: > On 12/1/21 10:16, Marek Polacek wrote: > > 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. > > > > So we need to be more careful about synthesizing the implicit template > > parameter. cp_parser_postfix_expression looked like a sensible place. > > Does this cover other uses of auto in decltype, such as > > void f(decltype(new auto{0})); Yes: the clearing of auto_is_implicit_function_template_parm_p will happen here too. However, I'm noticing this: 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); // error: no matching function for call to f1(int*) // couldn't deduce template parameter auto:1 f2 (&i); f3 (&i); f4 (&i); } I think the error we issue is bogus. (My patch doesn't change this. clang++ accepts.) Should I file a PR (and investigate)? > ? Should we adjust this flag in cp_parser_decltype along with all the other > flags? I think that's possible, but wouldn't cover auto in default arguments, or array bounds. Thanks, Marek
On 12/2/21 10:27, Marek Polacek wrote: > On Wed, Dec 01, 2021 at 11:24:58PM -0500, Jason Merrill wrote: >> On 12/1/21 10:16, Marek Polacek wrote: >>> 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. >>> >>> So we need to be more careful about synthesizing the implicit template >>> parameter. cp_parser_postfix_expression looked like a sensible place. >> >> Does this cover other uses of auto in decltype, such as >> >> void f(decltype(new auto{0})); > > Yes: the clearing of auto_is_implicit_function_template_parm_p will happen here > too. > > However, I'm noticing this: > > 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); // error: no matching function for call to f1(int*) > // couldn't deduce template parameter auto:1 > f2 (&i); > f3 (&i); > f4 (&i); > } > > I think the error we issue is bogus. (My patch doesn't change this. clang++ > accepts.) Should I file a PR (and investigate)? That certainly suggests that auto_is_implicit_function_template_parm_p isn't getting cleared soon enough for f1. >> ? Should we adjust this flag in cp_parser_decltype along with all the other >> flags? > > I think that's possible, but wouldn't cover auto in default arguments, or array > bounds. I guess cp_parser_sizeof_operand would need the same change. Do we currently handle auto in default arguments wrong? Ah, I see that we currently set auto_is_... for the whole parameter declaration clause, rather than just for the decl-specifier-seq of parameters as the standard specifies: "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...." Jason
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index 55e6a1a8b3a..c43b180f888 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -7508,6 +7508,8 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p, looking at a functional cast. We could also be looking at an id-expression. So, we try the functional cast, and if that doesn't work we fall back to the primary-expression. */ + auto cleanup = make_temp_override + (parser->auto_is_implicit_function_template_parm_p, false); cp_parser_parse_tentatively (parser); /* Look for the simple-type-specifier. */ ++parser->prevent_constrained_type_specifiers; diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C new file mode 100644 index 00000000000..763164f3e5b --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast7.C @@ -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" } +} diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C new file mode 100644 index 00000000000..760827a5d6e --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast8.C @@ -0,0 +1,28 @@ +// 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 +g () +{ + f1 (1); + f2 (1); + f3 (); + f3 (1); + f4 (); + f4 (1); + f5 (); + f5 (1); + f6 ('a'); + int a[10]; + f7 (&a[0]); + f8 (&a[0]); +}