[PATCH] c++: Fix P0846 (ADL and function templates) in template [PR97010]
Marek Polacek
polacek@redhat.com
Thu Sep 10 22:15:24 GMT 2020
To quickly recap, P0846 says that a name is also considered to refer to
a template if it is an unqualified-id followed by a < and name lookup
finds either one or more functions or finds nothing.
In a template, when parsing a function call that has type-dependent
arguments, we can't perform ADL right away so we set KOENIG_LOOKUP_P in
the call to remember to do it when instantiating the call
(tsubst_copy_and_build/CALL_EXPR). When the called function is a
function template, we represent the call with a TEMPLATE_ID_EXPR;
usually the operand is an OVERLOAD.
In the P0846 case though, the operand can be an IDENTIFIER_NODE, when
name lookup found nothing when parsing the template name. But we
weren't handling this correctly in tsubst_copy_and_build. First
we need to pass the FUNCTION_P argument from <case TEMPLATE_ID_EXPR> to
<case IDENTIFIER_NODE>, otherwise we give a bogus error. And then in
<case CALL_EXPR> we need to perform ADL. The rest of the changes is to
give better errors when ADL didn't find anything.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
I think I'd like to backport to 10 too.
gcc/cp/ChangeLog:
PR c++/97010
* pt.c (tsubst_copy_and_build) <case TEMPLATE_ID_EXPR>: Call
tsubst_copy_and_build explicitly instead of using the RECUR macro.
Handle a TEMPLATE_ID_EXPR with an IDENTIFIER_NODE as its operand.
<case CALL_EXPR>: Perform ADL for a TEMPLATE_ID_EXPR with an
IDENTIFIER_NODE as its operand.
gcc/testsuite/ChangeLog:
PR c++/97010
* g++.dg/cpp2a/fn-template21.C: New test.
* g++.dg/cpp2a/fn-template22.C: New test.
---
gcc/cp/pt.c | 37 ++++++++++++++++------
gcc/testsuite/g++.dg/cpp2a/fn-template21.C | 24 ++++++++++++++
gcc/testsuite/g++.dg/cpp2a/fn-template22.C | 25 +++++++++++++++
3 files changed, 77 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/fn-template21.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/fn-template22.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 30c6735dede..566e24f9bf3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -19241,7 +19241,8 @@ out:
}
/* Like tsubst but deals with expressions and performs semantic
- analysis. FUNCTION_P is true if T is the "F" in "F (ARGS)". */
+ analysis. FUNCTION_P is true if T is the "F" in "F (ARGS)" or
+ "F<TARGS> (ARGS)". */
tree
tsubst_copy_and_build (tree t,
@@ -19323,7 +19324,10 @@ tsubst_copy_and_build (tree t,
case TEMPLATE_ID_EXPR:
{
tree object;
- tree templ = RECUR (TREE_OPERAND (t, 0));
+ tree templ = tsubst_copy_and_build (TREE_OPERAND (t, 0), args,
+ complain, in_decl,
+ function_p,
+ integral_constant_expression_p);
tree targs = TREE_OPERAND (t, 1);
if (targs)
@@ -19370,13 +19374,21 @@ tsubst_copy_and_build (tree t,
}
else
object = NULL_TREE;
- templ = lookup_template_function (templ, targs);
+
+ tree tid = lookup_template_function (templ, targs);
if (object)
- RETURN (build3 (COMPONENT_REF, TREE_TYPE (templ),
- object, templ, NULL_TREE));
+ RETURN (build3 (COMPONENT_REF, TREE_TYPE (tid),
+ object, tid, NULL_TREE));
+ else if (identifier_p (templ))
+ {
+ /* C++20 P0846: we can encounter an IDENTIFIER_NODE here when
+ name lookup found nothing when parsing the template name. */
+ gcc_assert (cxx_dialect >= cxx20 || seen_error ());
+ RETURN (tid);
+ }
else
- RETURN (baselink_for_fns (templ));
+ RETURN (baselink_for_fns (tid));
}
case INDIRECT_REF:
@@ -19967,14 +19979,17 @@ tsubst_copy_and_build (tree t,
/* We do not perform argument-dependent lookup if normal
lookup finds a non-function, in accordance with the
- expected resolution of DR 218. */
+ resolution of DR 218. */
if (koenig_p
&& ((is_overloaded_fn (function)
/* If lookup found a member function, the Koenig lookup is
not appropriate, even if an unqualified-name was used
to denote the function. */
&& !DECL_FUNCTION_MEMBER_P (get_first_fn (function)))
- || identifier_p (function))
+ || identifier_p (function)
+ /* C++20 P0846: Lookup found nothing. */
+ || (TREE_CODE (function) == TEMPLATE_ID_EXPR
+ && identifier_p (TREE_OPERAND (function, 0))))
/* Only do this when substitution turns a dependent call
into a non-dependent call. */
&& type_dependent_expression_p_push (t)
@@ -19982,9 +19997,13 @@ tsubst_copy_and_build (tree t,
function = perform_koenig_lookup (function, call_args, tf_none);
if (function != NULL_TREE
- && identifier_p (function)
+ && (identifier_p (function)
+ || (TREE_CODE (function) == TEMPLATE_ID_EXPR
+ && identifier_p (TREE_OPERAND (function, 0))))
&& !any_type_dependent_arguments_p (call_args))
{
+ if (TREE_CODE (function) == TEMPLATE_ID_EXPR)
+ function = TREE_OPERAND (function, 0);
if (koenig_p && (complain & tf_warning_or_error))
{
/* For backwards compatibility and good diagnostics, try
diff --git a/gcc/testsuite/g++.dg/cpp2a/fn-template21.C b/gcc/testsuite/g++.dg/cpp2a/fn-template21.C
new file mode 100644
index 00000000000..7b3f26bbfa0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/fn-template21.C
@@ -0,0 +1,24 @@
+// PR c++/97010
+// { dg-do compile { target c++20 } }
+
+namespace M {
+ struct S { int x; };
+ S foo ();
+
+ template<typename>
+ void get (S);
+}
+
+template<typename T>
+void bar (const T& t)
+{
+ get<int>(t);
+}
+
+int
+main ()
+{
+ auto a = M::foo ();
+ get<int>(a);
+ bar (a);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/fn-template22.C b/gcc/testsuite/g++.dg/cpp2a/fn-template22.C
new file mode 100644
index 00000000000..62cc81db0c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/fn-template22.C
@@ -0,0 +1,25 @@
+// PR c++/97010
+// { dg-do compile { target c++20 } }
+
+namespace M {
+ struct S { int x; };
+ S foo ();
+
+// Test not-found-by-ADL scenario.
+// template<typename>
+// void get (S);
+}
+
+template<typename T>
+void bar (const T& t)
+{
+ get<int>(t); // { dg-error ".get. was not declared in this scope" }
+}
+
+int
+main ()
+{
+ auto a = M::foo ();
+ get<int>(a); // { dg-error ".get. was not declared in this scope" }
+ bar (a);
+}
base-commit: af47a2035a4882e6d4506e3d00b5a42414e3ee2b
--
2.26.2
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