[PATCH] c++: Fix P0846 (ADL and function templates) in template [PR97010]
Marek Polacek
polacek@redhat.com
Fri Sep 18 20:05:16 GMT 2020
Ping.
On Thu, Sep 10, 2020 at 06:15:24PM -0400, Marek Polacek via Gcc-patches wrote:
> 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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