[PATCH] c++: permit deduction guides at class scope [PR79501]
Patrick Palka
ppalka@redhat.com
Fri Jul 9 22:41:19 GMT 2021
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.
-- >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};
--
2.32.0.170.gd486ca60a5
More information about the Gcc-patches
mailing list