Re: [PATCH] Fix PR c++/66786 (ICE with nested lambdas in variable template)

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Mon, Feb 8, 2016 at 12:19 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> Here, we are calling template_class_depth on a FIELD_DECL corresponding
> to a lambda that is used inside variable template.  template_class_depth
> however does not see that this FIELD_DECL is used inside a variable
> template binding because its chain of DECL_CONTEXTs does not include the
> corresponding VAR_DECL.  So template_class_depth returns the wrong
> template nesting level which causes its callers to malfunction.  In
> particular we strip a template argument level in
> tsubst_copy [FIELD_DECL] when we shouldn't have.
>
> This patch makes template_class_depth look at a lambda type's
> LAMBDA_TYPE_EXTRA_SCOPE field instead of its TYPE_CONTEXT, so that it
> can iterate into an enclosing variable template, if applicable.
>
> Tested on x86_64-pc-linux gnu, no new regressions.  Also tested against
> Boost.  Is this OK to commit?
>
> gcc/cp/ChangeLog:
>
>         PR c++/66786
>         * pt.c (template_class_depth): Given a lambda type, iterate
>         into its LAMBDA_TYPE_EXTRA_SCOPE field instead of its
>         TYPE_CONTEXT.  Given a VAR_DECL, iterate into its
>         CP_DECL_CONTEXT.
>
> gcc/testsuite/ChangeLog:
>
>         PR c++/66786
>         * g++.dg/cpp1y/var-templ48.C: New test.
>         * g++.dg/cpp1y/var-templ49.C: New test.
> ---
>  gcc/cp/pt.c                              | 12 ++++++++----
>  gcc/testsuite/g++.dg/cpp1y/var-templ48.C |  5 +++++
>  gcc/testsuite/g++.dg/cpp1y/var-templ49.C |  9 +++++++++
>  3 files changed, 22 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ48.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ49.C
>
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index 4d405cf..5c344c1 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -369,16 +369,20 @@ template_class_depth (tree type)
>  {
>    int depth;
>
> -  for (depth = 0;
> -       type && TREE_CODE (type) != NAMESPACE_DECL;
> -       type = (TREE_CODE (type) == FUNCTION_DECL)
> -        ? CP_DECL_CONTEXT (type) : CP_TYPE_CONTEXT (type))
> +  for (depth = 0; type && TREE_CODE (type) != NAMESPACE_DECL; )
>      {
>        tree tinfo = get_template_info (type);
>
>        if (tinfo && PRIMARY_TEMPLATE_P (TI_TEMPLATE (tinfo))
>           && uses_template_parms (INNERMOST_TEMPLATE_ARGS (TI_ARGS (tinfo))))
>         ++depth;
> +
> +      if (VAR_OR_FUNCTION_DECL_P (type))
> +       type = CP_DECL_CONTEXT (type);
> +      else if (LAMBDA_TYPE_P (type))
> +       type = LAMBDA_TYPE_EXTRA_SCOPE (type);
> +      else
> +       type = CP_TYPE_CONTEXT (type);
>      }
>
>    return depth;
> diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ48.C b/gcc/testsuite/g++.dg/cpp1y/var-templ48.C
> new file mode 100644
> index 0000000..f0c7693
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ48.C
> @@ -0,0 +1,5 @@
> +// PR c++/66786
> +// { dg-do compile { target c++14 } }
> +
> +template <typename... T> auto list = [](T... xs) { [=](auto f) { f(xs...); }; };
> +int main() { list<int>(0); }
> diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ49.C b/gcc/testsuite/g++.dg/cpp1y/var-templ49.C
> new file mode 100644
> index 0000000..cd3f230
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ49.C
> @@ -0,0 +1,9 @@
> +// PR c++/66786
> +// { dg-do compile { target c++14 } }
> +
> +int f (int, bool);
> +
> +template <typename>
> +auto list = [](auto... xs) { return [=](auto f, auto... ys) { return f(xs..., ys...); }; };
> +
> +const int &a = list<int>(0, true)(f);
> --
> 2.7.1.257.g925a48d
>

Ping.