Consider
template <typename T> class A {
template <typename U> class B {
void fn(typename A<T>::B<U>);
};
};
which is rejected with
error: 'typename A<T>::B' names 'template<class T> template<class U> class
A<T>::B', which is not a type
whereas clang/icc/msvc accept it.
"typename A<T>::B<U>" is a typename-specifier. Sadly, our comments
don't mention it anywhere, because the typename-specifier wasn't in C++11;
it was only added to the language in N1376. Instead, we handle it as
an elaborated-type-specifier (not a problem thus far). So we get to
cp_parser_nested_name_specifier_opt which has a loop that breaks if we
don't see a < or ::, but that means we can -- tentatively -- parse even
B<U> which is not a nested-name-specifier (it doesn't end with a ::).
Even though we're parsing B<U> tentatively, we issue an error in
cp_parser_class_name -> make_typename_type, but here we should not. In
fact, we probably shouldn't have parsed "B<U>" at all. Fixed by the
cp_parser_class_name hunk.
I think this should compile because [temp.names]/4 says: "In a qualified-id
used as the name in a typename-specifier, elaborated-type-specifier,
using-declaration, or class-or-decltype, an optional keyword template
appearing at the top level is ignored.", added in DR 1710. Also see
DR 1812.
This issue on its own is not a significant problem or a regression.
However, in C++20, the typename here becomes optional, and so this test
is rejected in C++20, but accepted in C++17:
template <typename T> class A {
template <typename U> class B {
void fn(A<T>::B<U>);
};
};
Here we morph A<T>::B<U> into a typename-specifier, but that happens
in cp_parser_simple_type_specifier and we never handle it as above.
To fake the template keyword I'm afraid we need to use cp_parser_template_id
with template_keyword_p=true as in the patch below. The tricky thing
is to avoid breaking concepts.
Does this approach make sense? Should these tests be accepted because
of DR 1710 or am I off base here?
Apologies for the verbosity, but I felt it necessary.
Bootstrapped/regtested on x86_64-linux, built Boost/cmcstl2, ok for trunk?
PR c++/94057 - template keyword in a typename-specifier.
* parser.c (cp_parser_simple_type_specifier): Assume that a <
following a qualified-id in a typename-specifier begins
a template argument list.
(cp_parser_class_name): Complain only if not parsing tentatively.
* g++.dg/template/dependent-name5.C: Update dg-error.
* g++.dg/template/dependent-name7.C: New test.
* g++.dg/template/dependent-name8.C: New test.
* g++.dg/template/dependent-name9.C: New test.
---
gcc/cp/parser.c | 32 +++++++++++++++++--
.../g++.dg/template/dependent-name5.C | 2 --
.../g++.dg/template/dependent-name7.C | 9 ++++++
.../g++.dg/template/dependent-name8.C | 9 ++++++
.../g++.dg/template/dependent-name9.C | 9 ++++++
5 files changed, 57 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/dependent-name7.C
create mode 100644 gcc/testsuite/g++.dg/template/dependent-name8.C
create mode 100644 gcc/testsuite/g++.dg/template/dependent-name9.C
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index cbd5510a8fb..f4175955992 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -18113,6 +18113,33 @@ cp_parser_simple_type_specifier (cp_parser* parser,
}
}
}
+ /* DR 1812: A < following a qualified-id in a typename-specifier
+ could safely be assumed to begin a template argument list, so
+ the template keyword should be optional. */
+ else if (parser->scope
+ && qualified_p
+ && typename_p
+ && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))
+ {
+ cp_parser_parse_tentatively (parser);
+
+ type = cp_parser_template_id (parser,
+ /*template_keyword_p=*/true,
+ /*check_dependency_p=*/true,
+ none_type,
+ /*is_declaration=*/false);
+ /* This is handled below, so back off. */
+ if (type && concept_check_p (type))
+ cp_parser_simulate_error (parser);
+
+ if (!cp_parser_parse_definitely (parser))
+ type = NULL_TREE;
+ else if (TREE_CODE (type) == TEMPLATE_ID_EXPR)
+ type = make_typename_type (parser->scope, type, typename_type,
+ /*complain=*/tf_error);
+ else if (TREE_CODE (type) != TYPE_DECL)
+ type = NULL_TREE;
+ }
/* Otherwise, look for a type-name. */
if (!type)
@@ -23636,8 +23663,9 @@ cp_parser_class_name (cp_parser *parser,
&& decl != error_mark_node
&& !is_overloaded_fn (decl))
{
- decl = make_typename_type (scope, decl, typename_type,
- /*complain=*/tf_error);
+ tsubst_flags_t complain = (cp_parser_parsing_tentatively (parser)
+ ? tf_none : tf_error);
+ decl = make_typename_type (scope, decl, typename_type, complain);
if (decl != error_mark_node)
decl = TYPE_NAME (decl);
}
diff --git a/gcc/testsuite/g++.dg/template/dependent-name5.C
b/gcc/testsuite/g++.dg/template/dependent-name5.C
index fc78983324b..15c1acb0347 100644
--- a/gcc/testsuite/g++.dg/template/dependent-name5.C
+++ b/gcc/testsuite/g++.dg/template/dependent-name5.C
@@ -22,9 +22,7 @@ struct A
typedef N<int> type6;
typedef A::N<int> type7;
-// { dg-error "" "" { target c++2a } .-1 }
typedef A<T>::N<int> type8;
-// { dg-error "" "" { target c++2a } .-1 }
typedef A<T*>::template N<int> type9; // { dg-error "" "" { target
c++17_down } }
typedef typename A<T*>::template N<int> type10;
diff --git a/gcc/testsuite/g++.dg/template/dependent-name7.C
b/gcc/testsuite/g++.dg/template/dependent-name7.C
new file mode 100644
index 00000000000..3dfa42d2df0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/dependent-name7.C
@@ -0,0 +1,9 @@
+// PR c++/94057 - template keyword in a typename-specifier.
+// { dg-do compile }
+
+template<typename T> struct A {
+ template<typename U> struct B {
+ B(A<T>::B<U>&);
+ void fn(A<T>::B<U>);
+ };
+};
diff --git a/gcc/testsuite/g++.dg/template/dependent-name8.C
b/gcc/testsuite/g++.dg/template/dependent-name8.C
new file mode 100644
index 00000000000..ad9e44f9b85
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/dependent-name8.C
@@ -0,0 +1,9 @@
+// PR c++/94057 - template keyword in a typename-specifier.
+// { dg-do compile }
+
+template<typename T> struct A {
+ template<typename U> struct B {
+ B(typename A<T>::B<U>&);
+ void fn(typename A<T>::B<U>);
+ };
+};
diff --git a/gcc/testsuite/g++.dg/template/dependent-name9.C
b/gcc/testsuite/g++.dg/template/dependent-name9.C
new file mode 100644
index 00000000000..6dfdbc176c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/dependent-name9.C
@@ -0,0 +1,9 @@
+// PR c++/94057 - template keyword in a typename-specifier.
+// { dg-do compile }
+
+template<typename T> struct A {
+ template<typename U> struct B {
+ B(typename A<T>::template B<U>&);
+ void fn(typename A<T>::template B<U>);
+ };
+};
base-commit: f22712bd8a2ed57d3cc7e6fa92730bd5852e27b3
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
