Marek Polacek
6a071b2d40
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.
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