[PATCH] c++: permit deduction guides at class scope [PR79501]
Jason Merrill
jason@redhat.com
Fri Jul 9 19:54:11 GMT 2021
On 7/9/21 3:18 PM, Patrick Palka wrote:
> This adds support for declaring (class-scope) deduction guides for a
> member class template. Fortunately it seems only a couple of changes
> are needed in order for the existing CTAD machinery to handle them like
> any other deduction guide: we need to make sure to give them a
> FUNCTION_TYPE instead of a METHOD_TYPE, and we need to avoid using a
> BASELINK when looking them up.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
>
> PR c++/79501
>
> gcc/cp/ChangeLog:
>
> * decl.c (grokfndecl): Don't require that deduction guides are
> declared at namespace scope. Check that class-scope deduction
> guides have the same access as the member class template.
> (grokdeclarator): Pretend class-scope deduction guides are static.
> * name-lookup.c (lookup_qualified_name): Don't use a BASELINK
> for class-scope deduction guides.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp1z/class-deduction92.C: New test.
> * g++.dg/cpp1z/class-deduction93.C: New test.
> * g++.dg/cpp1z/class-deduction94.C: New test.
> ---
> gcc/cp/decl.c | 17 ++++++++-----
> gcc/cp/name-lookup.c | 11 +++++---
> .../g++.dg/cpp1z/class-deduction92.C | 16 ++++++++++++
> .../g++.dg/cpp1z/class-deduction93.C | 25 +++++++++++++++++++
> .../g++.dg/cpp1z/class-deduction94.C | 19 ++++++++++++++
> 5 files changed, 79 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction92.C
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction93.C
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction94.C
>
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index ebe1318d38d..8b8ffb7de83 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -10040,12 +10040,6 @@ grokfndecl (tree ctype,
>
> if (deduction_guide_p (decl))
> {
> - if (!DECL_NAMESPACE_SCOPE_P (decl))
> - {
> - error_at (location, "deduction guide %qD must be declared at "
> - "namespace scope", decl);
> - return NULL_TREE;
> - }
Do we still reject deduction guides at function scope?
> tree type = TREE_TYPE (DECL_NAME (decl));
> if (in_namespace == NULL_TREE
> && CP_DECL_CONTEXT (decl) != CP_TYPE_CONTEXT (type))
> @@ -10055,6 +10049,13 @@ grokfndecl (tree ctype,
> inform (location_of (type), " declared here");
> return NULL_TREE;
> }
> + if (DECL_CLASS_SCOPE_P (decl)
> + && current_access_specifier != declared_access (TYPE_NAME (type)))
> + {
> + error_at (location, "deduction guide %qD must have the same access "
> + "as %qT", decl, type);
> + inform (location_of (type), " declared here");
> + }
> if (funcdef_flag)
> error_at (location,
> "deduction guide %qD must not have a function body", decl);
> @@ -12035,6 +12036,10 @@ grokdeclarator (const cp_declarator *declarator,
> storage_class = declspecs->storage_class;
> if (storage_class == sc_static)
> staticp = 1 + (decl_context == FIELD);
> + else if (decl_context == FIELD && sfk == sfk_deduction_guide)
> + /* Treat class-scope deduction guides as static member functions
> + so that they get a FUNCTION_TYPE instead of a METHOD_TYPE. */
> + staticp = 2;
>
> if (virtualp)
> {
> diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
> index 1be5f3da6d5..089bca1d471 100644
> --- a/gcc/cp/name-lookup.c
> +++ b/gcc/cp/name-lookup.c
> @@ -7110,9 +7110,14 @@ lookup_qualified_name (tree scope, tree name, LOOK_want want, bool complain)
> else if (cxx_dialect != cxx98 && TREE_CODE (scope) == ENUMERAL_TYPE)
> t = lookup_enumerator (scope, name);
> else if (is_class_type (scope, complain))
> - t = lookup_member (scope, name, 2, bool (want & LOOK_want::TYPE),
> - tf_warning_or_error);
> -
> + {
> + t = lookup_member (scope, name, 2, bool (want & LOOK_want::TYPE),
> + tf_warning_or_error);
> + if (t && dguide_name_p (name))
> + /* Since class-scope deduction guides aren't really member functions,
> + don't use a BASELINK for them. */
> + t = MAYBE_BASELINK_FUNCTIONS (t);
> + }
> if (!t)
> return error_mark_node;
> return t;
> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction92.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction92.C
> new file mode 100644
> index 00000000000..178234c76d1
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction92.C
> @@ -0,0 +1,16 @@
> +// PR c++/79501
> +// { dg-do compile { target c++17 } }
> +
> +template<auto V>
> +struct X {
> + template<class T>
> + struct B { T t; };
> +
> + template<class T> B(T) -> B<const T>;
> +
> + auto foo() { return B{V}; }
> +};
> +
> +X<42> x;
> +using type = decltype(x.foo());
> +using type = X<42>::B<const int>;
> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction93.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction93.C
> new file mode 100644
> index 00000000000..9d2db7a55a2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction93.C
> @@ -0,0 +1,25 @@
> +// PR c++/79501
> +// { dg-do compile { target c++17 } }
> +// A variant of class-deduction78.C where List and its deduction guides are
> +// defined at class scope.
> +
> +using size_t = decltype(sizeof(42));
> +
> +struct A {
> + template<typename T, size_t N = 0>
> + struct List {
> + T head;
> + List<T, N-1> tail;
> + };
> +
> + template<typename T>
> + struct List<T, 0> {};
> +
> + template<typename T> List(T) -> List<T, 1>;
> + template<typename T, size_t N> List(T, List<T, N>) -> List<T, N+1>;
> +};
> +
> +int main() {
> + using type = decltype(A::List{0, A::List{1, A::List{2}}});
> + using type = A::List<int, 3>;
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction94.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction94.C
> new file mode 100644
> index 00000000000..f29ebd2c2b8
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction94.C
> @@ -0,0 +1,19 @@
> +// PR c++/79501
> +// { dg-do compile { target c++17 } }
> +
> +struct X {
> +protected:
> + template<class T>
> + struct B { T t; };
> +
> + template<class T> B(T) -> B<T>;
> +};
> +
> +struct Y {
> +protected:
> + template<class T>
> + struct B { T t; };
> +
> +private:
> + template<class T> B(T) -> B<T>; // { dg-error "access" }
> +};
>
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