c++: context completion in lookup_template_class [PR105982]
Commit Message
The below testcase demonstrates that completion of the substituted
context during lookup_template_class can end up registering the desired
specialization for us in more cases than r13-1045-gcb7fd1ea85feea
anticipated. In particular, it can happen for a non-dependent
specialization of a nested class as well.
During overload resolution with A's guides, we substitute the deduced
argument T=int into the TYPENAME_TYPE B::C (*). This substitution calls
lookup_template_class for A<T>::B with T=int, which completes A<int>
for the first time, which recursively registers the desired specialization
of B for us. The parent call to lookup_template_class then tries
registering the same specialization, which leads to a crash.
This patch fixes this by making lookup_template_class check the
specializations table after completion of the context iff necessary,
i.e. when the call to complete_type actually has an effect.
(*): Note that the TYPE_CONTEXT of this TYPENAME_TYPE is just the
RECORD_TYPE B instead of TYPENAME_TYPE A<T>::B. Is this expected?
I'd think maybe_dependent_member_ref would rewrite the reference to B
in terms of another TYPENAME_TYPE. This is why the testcase needs to
use 'typename B::C' instead of just 'B' -- maybe_dependent_member_ref
rewrites the use of B in the latter case but not the former.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
PR c++/105982
gcc/cp/ChangeLog:
* pt.cc (lookup_template_class): After completion of the
substituted context, check the table again iff the type was
previously incomplete and complete_type made it complete.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1z/class-deduction111.C: New test.
---
gcc/cp/pt.cc | 21 +++++++++++--------
.../g++.dg/cpp1z/class-deduction111.C | 10 +++++++++
2 files changed, 22 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction111.C
Comments
On 6/23/22 10:48, Patrick Palka wrote:
> The below testcase demonstrates that completion of the substituted
> context during lookup_template_class can end up registering the desired
> specialization for us in more cases than r13-1045-gcb7fd1ea85feea
> anticipated. In particular, it can happen for a non-dependent
> specialization of a nested class as well.
>
> During overload resolution with A's guides, we substitute the deduced
> argument T=int into the TYPENAME_TYPE B::C (*). This substitution calls
> lookup_template_class for A<T>::B with T=int, which completes A<int>
> for the first time, which recursively registers the desired specialization
> of B for us. The parent call to lookup_template_class then tries
> registering the same specialization, which leads to a crash.
>
> This patch fixes this by making lookup_template_class check the
> specializations table after completion of the context iff necessary,
> i.e. when the call to complete_type actually has an effect.
>
> (*): Note that the TYPE_CONTEXT of this TYPENAME_TYPE is just the
> RECORD_TYPE B instead of TYPENAME_TYPE A<T>::B. Is this expected?
> I'd think maybe_dependent_member_ref would rewrite the reference to B
> in terms of another TYPENAME_TYPE. This is why the testcase needs to
> use 'typename B::C' instead of just 'B' -- maybe_dependent_member_ref
> rewrites the use of B in the latter case but not the former.
Hmm, perhaps maybe_dependent_member_ref needs to consider rewriting ctx
as well.
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
OK.
> PR c++/105982
>
> gcc/cp/ChangeLog:
>
> * pt.cc (lookup_template_class): After completion of the
> substituted context, check the table again iff the type was
> previously incomplete and complete_type made it complete.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp1z/class-deduction111.C: New test.
> ---
> gcc/cp/pt.cc | 21 +++++++++++--------
> .../g++.dg/cpp1z/class-deduction111.C | 10 +++++++++
> 2 files changed, 22 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction111.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 28edc6ae988..eeae867a816 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -10089,16 +10089,19 @@ lookup_template_class (tree d1, tree arglist, tree in_decl, tree context,
> {
> context = tsubst_aggr_type (context, arglist,
> complain, in_decl, true);
> - context = complete_type (context);
> - if (is_dependent_type && arg_depth > 1)
> + /* Try completing the enclosing context if it's not already so. */
> + if (context != error_mark_node
> + && !COMPLETE_TYPE_P (context))
> {
> + context = complete_type (context);
> + if (COMPLETE_TYPE_P (context))
> + {
> + /* Completion could have caused us to register the desired
> + specialization for us, so check the table again. */
> + entry = type_specializations->find_with_hash (&elt, hash);
> + if (entry)
> + return entry->spec;
> + }
> }
> }
> }
> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C
> new file mode 100644
> index 00000000000..2406529ea5a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C
> @@ -0,0 +1,10 @@
> +// PR c++/105982
> +// { dg-do compile { target c++17 } }
> +
> +template<class T>
> +struct A {
> + struct B { struct C { }; };
> + A(T, typename B::C);
> +};
> +
> +A a(0, {});
@@ -10089,16 +10089,19 @@ lookup_template_class (tree d1, tree arglist, tree in_decl, tree context,
{
context = tsubst_aggr_type (context, arglist,
complain, in_decl, true);
- context = complete_type (context);
- if (is_dependent_type && arg_depth > 1)
+ /* Try completing the enclosing context if it's not already so. */
+ if (context != error_mark_node
+ && !COMPLETE_TYPE_P (context))
{
- /* If this is a dependent nested specialization such as
- A<T>::B<U> [with T=int, U=U], then completion of A<int>
- could have caused to register the desired specialization
- of B already, so check the table again (33959). */
- entry = type_specializations->find_with_hash (&elt, hash);
- if (entry)
- return entry->spec;
+ context = complete_type (context);
+ if (COMPLETE_TYPE_P (context))
+ {
+ /* Completion could have caused us to register the desired
+ specialization for us, so check the table again. */
+ entry = type_specializations->find_with_hash (&elt, hash);
+ if (entry)
+ return entry->spec;
+ }
}
}
}
new file mode 100644
@@ -0,0 +1,10 @@
+// PR c++/105982
+// { dg-do compile { target c++17 } }
+
+template<class T>
+struct A {
+ struct B { struct C { }; };
+ A(T, typename B::C);
+};
+
+A a(0, {});