Re: [PATCH] c++: enum in generic lambda at global scope [PR105398]

[Patrick Palka <ppalka@redhat.com>]

On Tue, 26 Apr 2022, Marek Polacek via Gcc-patches wrote:

> We crash compiling this test since r11-7993 which changed
> lookup_template_class_1 so that we only call tsubst_enum when
> 
>   !uses_template_parms (current_nonlambda_scope ())
> 
> But here current_nonlambda_scope () is the global NAMESPACE_DECL ::, which
> doesn't have a type, therefore is considered type-dependent.  So we don't
> call tsubst_enum, and crash in tsubst_copy/CONST_DECL because we didn't
> find the e1 enumerator.
> 
> I don't think any namespace can depend on any template parameter, so
> this patch tweaks uses_template_parms.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11?
> 
> 	PR c++/105398
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (uses_template_parms): Return false for any NAMESPACE_DECL.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp1y/lambda-generic-enum2.C: New test.
> ---
>  gcc/cp/pt.cc                                      |  2 +-
>  gcc/testsuite/g++.dg/cpp1y/lambda-generic-enum2.C | 15 +++++++++++++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp1y/lambda-generic-enum2.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 3cf1d7af8d2..e785c5db142 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -10905,7 +10905,7 @@ uses_template_parms (tree t)
>  		   || uses_template_parms (TREE_CHAIN (t)));
>    else if (TREE_CODE (t) == TYPE_DECL)
>      dependent_p = dependent_type_p (TREE_TYPE (t));
> -  else if (t == error_mark_node)
> +  else if (t == error_mark_node || TREE_CODE (t) == NAMESPACE_DECL)

LGTM.  In passing, perhaps we should move this t == error_mark_node test
to the beginning of the function alongside the t == NULL_TREE test?

>      dependent_p = false;
>    else
>      dependent_p = instantiation_dependent_expression_p (t);
> diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-enum2.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-enum2.C
> new file mode 100644
> index 00000000000..77cf0bb9d02
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-enum2.C
> @@ -0,0 +1,15 @@
> +// PR c++/105398
> +// { dg-do compile { target c++14 } }
> +
> +auto f = [](auto &&m) {
> +    enum E { _,e3,e2,e1,C4,C3,C2,C1 };
> +    static constexpr int x_coeffs[3][4] = {
> +        {e1,C2,C3,C4},
> +        {e2,C1,C3,C4},
> +        {e3,C1,C2,C4},
> +    };
> +};
> +
> +int main() {
> +    f(0);
> +}
> 
> base-commit: 9ace5d4dab2ab39072b0f07089621a823580f27c
> -- 
> 2.35.1
> 
>