Hi,
On Fri, 28 Feb 2025, Da Xie wrote:
> This bug comes from a missing check when a function declaration has a
> late-specified return type and a constrained auto type specifier. By
> adding such a check, we can catch such uses and diagnose them as errors.
>
> Successfully bootstrapped and regretested on x86_64-pc-linux-gnu:
> adds 6 new test results and 4 UNSUPPORTED results to g++.sum. The 4
> UNSUPPORTED results are due to the fact that concepts are not supported
> before c++20, so tests cannot pass with c++17 and lower standards.
>
> PR c++/100589
>
> gcc/cp/ChangeLog:
>
> * decl.cc (grokdeclarator): Issue an error for a declarator with
> constrained auto type specifier and trailing return types.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/other/pr100589.C: New test.
Thanks for the patch! Looks good to me overall, some minor comments
below.
>
> Signed-off-by: Da Xie <xxie...@163.com>
> ---
> gcc/cp/decl.cc | 7 +++++++
> gcc/testsuite/g++.dg/other/pr100589.C | 7 +++++++
> 2 files changed, 14 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/other/pr100589.C
>
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 9ca8c6c4481..f283ed996a2 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -14037,6 +14037,13 @@ grokdeclarator (const cp_declarator *declarator,
> "invalid use of %<decltype(auto)%>");
> return error_mark_node;
> }
> + else if (is_constrained_auto (type))
> + {
> + error_at (typespec_loc, "invalid use of "
> + "constrained auto type specifier "
> + "in function with trailing return type");
We should quote the 'auto' in this diagnostic by writing %<auto%>
for consistency with the other diagnostics.
> + return error_mark_node;
> + }
> tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node);
> if (!tmpl)
> if (tree late_auto = type_uses_auto (late_return_type))
> diff --git a/gcc/testsuite/g++.dg/other/pr100589.C
> b/gcc/testsuite/g++.dg/other/pr100589.C
> new file mode 100644
> index 00000000000..3fa054ed34d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/other/pr100589.C
Since this is a concepts-specific test let's name it
g++.dg/cpp2a/concepts-pr100589.C
> @@ -0,0 +1,7 @@
> +// PR c++/100589
> +// { dg-do compile { target c++20 } }
> +
> +template<class T>
> +concept false_concept = false;
> +
> +false_concept auto f() -> int; // { dg-error "constrained auto type
> specifier.* trailing return type" }
It'd be good to also test a bare function type:
using type = false_concept auto() -> int;
> \ No newline at end of file
> --
> 2.34.1
>
>
