[PATCH] c++: permit deduction guides at class scope [PR79501]
Jason Merrill
jason@redhat.com
Mon Jul 12 19:41:18 GMT 2021
On 7/9/21 6:41 PM, Patrick Palka wrote:
> On Fri, 9 Jul 2021, Jason Merrill wrote:
>
>> On 7/9/21 4:18 PM, Patrick Palka wrote:
>>> 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)?
>>
>> Avoiding building the baselink in lookup_member does sound better than
>> stripping it again here.
>
> That works well, like so? I also added the testcase from PR100983.
> Bootstrapped and regtested on x86_64-pc-linux-gnu.
OK.
> -- >8 --
>
> PR c++/79501
> PR c++/100983
>
> 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.
> * search.c (lookup_member): 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.
> * g++.dg/cpp1z/class-deduction95.C: New test.
> ---
> gcc/cp/decl.c | 17 ++++++++-----
> gcc/cp/search.c | 5 +++-
> .../g++.dg/cpp1z/class-deduction92.C | 16 ++++++++++++
> .../g++.dg/cpp1z/class-deduction93.C | 25 +++++++++++++++++++
> .../g++.dg/cpp1z/class-deduction94.C | 19 ++++++++++++++
> .../g++.dg/cpp1z/class-deduction95.C | 13 ++++++++++
> 6 files changed, 88 insertions(+), 7 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
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction95.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;
> - }
> 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/search.c b/gcc/cp/search.c
> index 7b183685476..af41bfe5835 100644
> --- a/gcc/cp/search.c
> +++ b/gcc/cp/search.c
> @@ -1226,7 +1226,10 @@ lookup_member (tree xbasetype, tree name, int protect, bool want_type,
> rval = error_mark_node;
> }
>
> - if (rval && is_overloaded_fn (rval))
> + if (rval && is_overloaded_fn (rval)
> + /* Don't use a BASELINK for class-scope deduction guides since
> + they're not actually member functions. */
> + && !dguide_name_p (name))
> rval = build_baselink (rval_binfo, basetype_path, rval,
> (IDENTIFIER_CONV_OP_P (name)
> ? TREE_TYPE (name): NULL_TREE));
> 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..78e76a6ab7b
> --- /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, auto>
> + struct B { T t; };
> +
> + template<class T> B(T, int=V) -> B<const T, V>;
> +
> + auto foo() { return B{V}; }
> +};
> +
> +X<42> x;
> +using type = decltype(x.foo());
> +using type = X<42>::B<const int, 42>;
> 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" }
> +};
> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction95.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction95.C
> new file mode 100644
> index 00000000000..afeb4a0d136
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction95.C
> @@ -0,0 +1,13 @@
> +// PR c++/100983
> +// { dg-do compile { target c++17 } }
> +
> +struct X {
> + template<int N>
> + struct Y {
> + template<class... Ts> Y(Ts...);
> + };
> +
> + template<class... Ts> Y(Ts...) -> Y<sizeof...(Ts)>;
> +};
> +
> +X::Y y{1,2,3};
>
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