[PATCH v3] c++: Member template function lookup failure [PR94799]
Marek Polacek
polacek@redhat.com
Mon May 4 20:37:12 GMT 2020
On Fri, May 01, 2020 at 04:12:35PM -0400, Jason Merrill wrote:
> > @@ -7754,9 +7755,22 @@ cp_parser_postfix_dot_deref_expression (cp_parser *parser,
> > }
> > if (dependent_p)
> > - /* Tell cp_parser_lookup_name that there was an object, even though it's
> > - type-dependent. */
> > - parser->context->object_type = unknown_type_node;
> > + {
> > + /* If we don't have a (type-dependent) object of class type, use
> > + decltype to signal that there was an object. */
> > + if (type == NULL_TREE)
> > + {
> > + type = finish_decltype_type (postfix_expression,
> > + /*member_access_p=*/true,
>
> This should be false, we don't want the special decltype semantics for a
> member-access expression.
Fixed.
> > + tf_warning_or_error);
> > + /* For -> this decltype will produce T*, but we want T. */
> > + if (token_type == CPP_DEREF)
> > + type = build_min_nt_loc (start_loc, INDIRECT_REF, type);
>
> Don't we want the INDIRECT_REF inside the decltype? How does it work like
> this?
I'm now not quite sure what I perpetrated there; I must've messed it up when I was
looking at what we do with it in the debugger. I assume it worked by accident.
I've moved the INDIRECT_REF inside the decltype, but I had to use the original
expression, and also set DECLTYPE_FOR_LAMBDA_CAPTURE so that the result of the
decltype is e.g. M<T>, not M<T> &. Not sure how hacky this is, but I've
verified that tsubst/TYPENAME_TYPE now gets what I would expect it to.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Whew, this took a while. We fail to parse "p->template A<T>::a()"
(where p is of type A<T> *) because since r249752 we treat the RHS of the ->
as dependent and avoid a lookup in the enclosing context: since that rev
cp_parser_template_name checks parser->context->object_type too, which
here is unknown_type_node, signalling a type-dependent object:
7756 if (dependent_p)
7757 /* Tell cp_parser_lookup_name that there was an object, even though it's
7758 type-dependent. */
7759 parser->context->object_type = unknown_type_node;
with which cp_parser_template_name returns identifier 'A', cp_parser_class_name
then creates a TEMPLATE_ID_EXPR A<T>, but then
23735 decl = make_typename_type (scope, decl, tag_type, tf_error);
in cp_parser_class_name fails because scope is NULL. Then we return
error_mark_node and parse errors ensue.
I've tried various approaches, e.g. keeping TEMPLATE_ID_EXPR around
instead of calling make_typename_type, which didn't work, whereupon I
realized that since we don't want to perform name lookup if we've seen
the template keyword and the scope is dependent, we can adjust
parser->context->object_type and use the type of the object expression
as the scope, even if it's type-dependent. This should be in line with
[basic.lookup.classref]p4. If the postfix expression doesn't have a type,
use decltype (possibly dereferenced) to carry its type. This decltype
will be processed in tsubst/TYPENAME_TYPE.
PR c++/94799
* parser.c (cp_parser_postfix_dot_deref_expression): If we have
a type-dependent object of class type, stash it to
parser->context->object_type. If the postfix expression doesn't have
a type, use decltype.
(cp_parser_class_name): Consider object scope too.
(cp_parser_lookup_name): Remove code dealing with the case when
object_type is unknown_type_node.
* g++.dg/lookup/this1.C: Adjust dg-error.
* g++.dg/template/lookup12.C: New test.
* g++.dg/template/lookup13.C: New test.
* g++.dg/template/lookup14.C: New test.
* g++.dg/template/lookup15.C: New test.
---
gcc/cp/parser.c | 39 ++++++++++++++++++------
gcc/testsuite/g++.dg/lookup/this1.C | 2 +-
gcc/testsuite/g++.dg/template/lookup12.C | 26 ++++++++++++++++
gcc/testsuite/g++.dg/template/lookup13.C | 28 +++++++++++++++++
gcc/testsuite/g++.dg/template/lookup14.C | 11 +++++++
gcc/testsuite/g++.dg/template/lookup15.C | 24 +++++++++++++++
6 files changed, 120 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/lookup12.C
create mode 100644 gcc/testsuite/g++.dg/template/lookup13.C
create mode 100644 gcc/testsuite/g++.dg/template/lookup14.C
create mode 100644 gcc/testsuite/g++.dg/template/lookup15.C
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 337f22d2784..673f3622125 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7694,6 +7694,7 @@ cp_parser_postfix_dot_deref_expression (cp_parser *parser,
bool pseudo_destructor_p;
tree scope = NULL_TREE;
location_t start_loc = postfix_expression.get_start ();
+ tree orig_expr = postfix_expression;
/* If this is a `->' operator, dereference the pointer. */
if (token_type == CPP_DEREF)
@@ -7754,9 +7755,26 @@ cp_parser_postfix_dot_deref_expression (cp_parser *parser,
}
if (dependent_p)
- /* Tell cp_parser_lookup_name that there was an object, even though it's
- type-dependent. */
- parser->context->object_type = unknown_type_node;
+ {
+ tree type = TREE_TYPE (orig_expr);
+ /* If we don't have a (type-dependent) object of class type, use
+ decltype to figure out the type of the object. Use the original
+ expression -- decltype on an ARROW_EXPR may not give the desirable
+ result. */
+ if (type == NULL_TREE)
+ {
+ /* For -> this decltype will produce T*, but we want T. */
+ if (token_type == CPP_DEREF)
+ orig_expr = build_min_nt_loc (start_loc, INDIRECT_REF, orig_expr);
+ type = finish_decltype_type (orig_expr, /*member_access_p=*/false,
+ tf_warning_or_error);
+ /* We don't want the result to be of reference type. */
+ DECLTYPE_FOR_LAMBDA_CAPTURE (type) = true;
+ }
+ else if (token_type == CPP_DEREF && POINTER_TYPE_P (type))
+ type = TREE_TYPE (type);
+ parser->context->object_type = type;
+ }
/* Assume this expression is not a pseudo-destructor access. */
pseudo_destructor_p = false;
@@ -23625,8 +23643,15 @@ cp_parser_class_name (cp_parser *parser,
}
/* PARSER->SCOPE can be cleared when parsing the template-arguments
- to a template-id, so we save it here. */
- scope = parser->scope;
+ to a template-id, so we save it here. Consider object scope too,
+ so that make_typename_type below can use it (cp_parser_template_name
+ considers object scope also). This may happen with code like
+
+ p->template A<T>::a()
+
+ where we first want to look up A<T>::a in the class of the object
+ expression, as per [basic.lookup.classref]. */
+ scope = parser->scope ? parser->scope : parser->context->object_type;
if (scope == error_mark_node)
return error_mark_node;
@@ -28340,10 +28365,6 @@ cp_parser_lookup_name (cp_parser *parser, tree name,
decl = lookup_name_real (name, prefer_type_arg (tag_type, is_template),
/*nonclass=*/0,
/*block_p=*/true, is_namespace, 0);
- if (object_type == unknown_type_node)
- /* The object is type-dependent, so we can't look anything up; we used
- this to get the DR 141 behavior. */
- object_type = NULL_TREE;
parser->object_scope = object_type;
parser->qualifying_scope = NULL_TREE;
}
diff --git a/gcc/testsuite/g++.dg/lookup/this1.C b/gcc/testsuite/g++.dg/lookup/this1.C
index 20051bf7515..6b85cefcd37 100644
--- a/gcc/testsuite/g++.dg/lookup/this1.C
+++ b/gcc/testsuite/g++.dg/lookup/this1.C
@@ -4,5 +4,5 @@
struct A
{
template<int> static void foo();
- static void bar() { this->A::foo<0>(); } // { dg-error "unavailable" }
+ static void bar() { this->A::foo<0>(); } // { dg-error "unavailable|not a class|expected" }
};
diff --git a/gcc/testsuite/g++.dg/template/lookup12.C b/gcc/testsuite/g++.dg/template/lookup12.C
new file mode 100644
index 00000000000..fc5939ab0f6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/lookup12.C
@@ -0,0 +1,26 @@
+// PR c++/94799 - member template function lookup fails.
+
+template<typename T> struct B {
+ void foo ();
+ int i;
+};
+
+template<typename T>
+struct D : public B<T> { };
+
+template<typename T>
+void fn (D<T> d)
+{
+ d.template B<T>::foo ();
+ d.template B<T>::i = 42;
+ D<T>().template B<T>::foo ();
+ d.template D<T>::template B<T>::foo ();
+ d.template D<T>::template B<T>::i = 10;
+}
+
+int
+main ()
+{
+ D<int> d;
+ fn(d);
+}
diff --git a/gcc/testsuite/g++.dg/template/lookup13.C b/gcc/testsuite/g++.dg/template/lookup13.C
new file mode 100644
index 00000000000..a8c7e18a707
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/lookup13.C
@@ -0,0 +1,28 @@
+// PR c++/94799 - member template function lookup fails.
+
+template <typename T>
+struct A {
+ int a() {
+ return 42;
+ }
+
+ template<typename> struct X { typedef int type; };
+};
+
+template <typename T>
+struct B {
+ int b(A<T> *p) {
+ int i = 0;
+ i += p->a();
+ i += p->template A<T>::a();
+ i += p->template A<T>::template A<T>::a();
+ i += A<T>().template A<T>::a();
+ return i;
+ }
+};
+
+int main() {
+ A<int> a;
+ B<int> b;
+ return b.b(&a);
+}
diff --git a/gcc/testsuite/g++.dg/template/lookup14.C b/gcc/testsuite/g++.dg/template/lookup14.C
new file mode 100644
index 00000000000..e1c945a6dca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/lookup14.C
@@ -0,0 +1,11 @@
+// PR c++/94799 - member template function lookup fails.
+
+template<typename T>
+struct A { };
+
+template<typename T>
+void fn (A<T> a)
+{
+ // Don't perform name lookup of foo when parsing this template.
+ a.template A<T>::foo ();
+}
diff --git a/gcc/testsuite/g++.dg/template/lookup15.C b/gcc/testsuite/g++.dg/template/lookup15.C
new file mode 100644
index 00000000000..c7f3ba01576
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/lookup15.C
@@ -0,0 +1,24 @@
+// PR c++/94799 - member template function lookup fails.
+
+template<typename>
+struct M { void fn() { } };
+
+M<int>* bar (int);
+M<int> bar2 (int);
+
+template<typename T>
+struct X : M<T> {
+ void xfn ()
+ {
+ this->template M<T>::fn ();
+ bar((T)1)->template M<T>::fn ();
+ bar2((T)1).template M<T>::fn ();
+ }
+};
+
+int
+main ()
+{
+ X<int> x;
+ x.xfn();
+}
base-commit: e6b31fc717207565f144aaefa608344789221f07
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
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