Hi,
On Sat, 22 Apr 2023, Nathaniel Shead via Gcc-patches wrote:
> Bootstrapped and tested on x86_64-pc-linux-gnu.
>
> -- 8< --
>
> This patch raises an error early when the decltype(auto) specifier is
> used as a parameter of a function. This prevents any issues with an
> unexpected tree type later on when performing the call.
Thanks very much for the patch! Some minor comments below.
>
> PR 103497
We should include the bug component name when referring to the PR in the
commit message (i.e. PR c++/103497) so that upon pushing the patch the
post-commit hook automatically adds a comment to the PR reffering to the
commit. I could be wrong but AFAIK the hook only performs this when the
component name is included.
>
> gcc/cp/ChangeLog:
>
> * parser.cc (cp_parser_simple_type_specifier): Add check for
> decltype(auto) as function parameter.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/pr103497.C: New test.
>
> Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> ---
> gcc/cp/parser.cc | 10 ++++++++++
> gcc/testsuite/g++.dg/pr103497.C | 7 +++++++
> 2 files changed, 17 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/pr103497.C
>
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index e5f032f2330..1415e07e152 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -19884,6 +19884,16 @@ cp_parser_simple_type_specifier (cp_parser* parser,
> && cp_lexer_peek_nth_token (parser->lexer, 2)->type != CPP_SCOPE)
> {
> type = saved_checks_value (token->u.tree_check_value);
> + /* Within a function parameter declaration, decltype(auto) is always an
> + error. */
> + if (parser->auto_is_implicit_function_template_parm_p
> + && TREE_CODE (type) == TEMPLATE_TYPE_PARM
We could check is_auto (type) here instead, to avoid any confusion with
checking AUTO_IS_DECLTYPE for a non-auto TEMPLATE_TYPE_PARM.
> + && AUTO_IS_DECLTYPE (type))
> + {
> + error_at (token->location,
> + "cannot declare a parameter with %<decltype(auto)%>");
> + type = error_mark_node;
> + }
> if (decl_specs)
> {
> cp_parser_set_decl_spec_type (decl_specs, type,
> diff --git a/gcc/testsuite/g++.dg/pr103497.C b/gcc/testsuite/g++.dg/pr103497.C
> new file mode 100644
> index 00000000000..bcd421c2907
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/pr103497.C
> @@ -0,0 +1,7 @@
> +// { dg-do compile { target c++14 } }
> +
> +void foo(decltype(auto)... args); // { dg-error "parameter with
> .decltype.auto..|no parameter packs" }
I noticed for
void foo(decltype(auto) arg);
we already issue an identical error from grokdeclarator. Perhaps we could
instead extend the error handling there to detect decltype(auto)... as well,
rather than adding new error handling in cp_parser_simple_type_specifier?
> +
> +int main() {
> + foo();
> +}
> --
> 2.34.1
>
>
