On Fri, 9 Jul 2021, Patrick Palka wrote:
> On Fri, 9 Jul 2021, Jason Merrill wrote:
>
> > 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?
>
> Yes, it looks like the parser doesn't even recognize them at function scope:
>
> template<class T> struct A;
>
> int main() {
> A(int) -> A<int>;
> }
>
> <stdin>:4:4: error: missing template arguments before ‘(’ token
> <stdin>:4:5: error: expected primary-expression before ‘int’
> <stdin>:4:13: error: invalid use of ‘struct A<int>’
>
> Deduction guide templates are also still rejected (as with all templates 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);
> > > + }
On second thought, this seems to be an awkward spot to do this
adjustment. Maybe it's better to do it in lookup_member, or in
deduction_guides_for (the only caller which really needs it)?
> > > 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" }
> > > +};
> > >
> >
> >
