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

[Patrick Palka <patrick@parcs.ath.cx>]

On Mon, Feb 15, 2016 at 9:42 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> 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.

Ping