Re: [PATCH 2/2] Fix handling of namespace-scope undeduced auto decls.

[Jason Merrill <jason at redhat dot com>]

On Fri, Aug 23, 2019 at 4:18 PM Jason Merrill <jason@redhat.com> wrote:

Apparently git send-email only spawns the editor once, so I need to
edit both messages before exiting...

This testcase comes from committee reflector discussion: 'fn' can't be
dependent because it is not in the scope of any template parameters.

Tested x86_64-pc-linux-gnu, applying to trunk.

>         * decl2.c (decl_dependent_p): New.
>         (mark_used): Check it instead of just processing_template_decl.
> ---
>  gcc/cp/decl2.c                              | 24 ++++++++++++++++++++-
>  gcc/testsuite/g++.dg/cpp1z/constexpr-if30.C | 10 +++++++++
>  gcc/cp/ChangeLog                            |  5 +++++
>  3 files changed, 38 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if30.C
>
> diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
> index a32108f9d16..134f6d6e3df 100644
> --- a/gcc/cp/decl2.c
> +++ b/gcc/cp/decl2.c
> @@ -5407,6 +5407,25 @@ cp_warn_deprecated_use (tree decl, tsubst_flags_t complain)
>    return warned;
>  }
>
> +/* True if DECL or its enclosing scope have unbound template parameters.  */
> +
> +bool
> +decl_dependent_p (tree decl)
> +{
> +  if (DECL_FUNCTION_SCOPE_P (decl)
> +      || TREE_CODE (decl) == CONST_DECL
> +      || TREE_CODE (decl) == USING_DECL
> +      || TREE_CODE (decl) == FIELD_DECL)
> +    decl = CP_DECL_CONTEXT (decl);
> +  if (tree tinfo = get_template_info (decl))
> +    if (any_dependent_template_arguments_p (TI_ARGS (tinfo)))
> +      return true;
> +  if (LAMBDA_FUNCTION_P (decl)
> +      && dependent_type_p (DECL_CONTEXT (decl)))
> +    return true;
> +  return false;
> +}
> +
>  /* Mark DECL (either a _DECL or a BASELINK) as "used" in the program.
>     If DECL is a specialization or implicitly declared class member,
>     generate the actual definition.  Return false if something goes
> @@ -5433,6 +5452,9 @@ mark_used (tree decl, tsubst_flags_t complain)
>        decl = OVL_FIRST (decl);
>      }
>
> +  if (!DECL_P (decl))
> +    return true;
> +
>    /* Set TREE_USED for the benefit of -Wunused.  */
>    TREE_USED (decl) = 1;
>    /* And for structured bindings also the underlying decl.  */
> @@ -5480,7 +5502,7 @@ mark_used (tree decl, tsubst_flags_t complain)
>        || DECL_LANG_SPECIFIC (decl) == NULL
>        || DECL_THUNK_P (decl))
>      {
> -      if (!processing_template_decl
> +      if (!decl_dependent_p (decl)
>           && !require_deduced_type (decl, complain))
>         return false;
>        return true;
> diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if30.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if30.C
> new file mode 100644
> index 00000000000..1e3d15dca1c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if30.C
> @@ -0,0 +1,10 @@
> +// { dg-do compile { target c++17 } }
> +
> +auto fn = [](auto i) {
> +    if constexpr (sizeof(i) == 1)
> +        return fn(123);                // { dg-error "auto" }
> +};
> +
> +int main() {
> +    fn('!');
> +}
> diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
> index d07c0de82dd..e6c83b5338e 100644
> --- a/gcc/cp/ChangeLog
> +++ b/gcc/cp/ChangeLog
> @@ -1,3 +1,8 @@
> +2019-08-22  Jason Merrill  <jason@redhat.com>
> +
> +       * decl2.c (decl_dependent_p): New.
> +       (mark_used): Check it instead of just processing_template_decl.
> +
>  2019-08-22  Jason Merrill  <jason@redhat.com>
>
>         * parser.c (cp_parser_nested_name_specifier_opt): Avoid redundant
> --
> 2.21.0
>