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c++: Set the constraints of a class type sooner [PR96229]

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In the testcase below, during processing (at parse time) of Y's base
class X<Y>, convert_template_argument calls is_compatible_template_arg
to check if the template argument Y is no more constrained than the
parameter P.  But at this point we haven't yet set Y's constraints, so
get_normalized_constraints_from_decl yields NULL_TREE as the normal form
and caches this result into the normalized_map.

We set Y's constraints later in cp_parser_class_specifier_1 but the
stale normal form in the normalized_map remains.  This ultimately causes
us to miss the constraint failure for Y<Z> because according to the
cached normal form, Y is not constrained.

This patch fixes this issue by moving up the call to
associate_classtype_constraints so that we set constraints before we
start processing a class's bases.

gcc/cp/ChangeLog:

	PR c++/96229
	* parser.c (cp_parser_class_specifier_1): Move call to
	associate_classtype_constraints from here to ...
	(cp_parser_class_head): ... here.
	* pt.c (is_compatible_template_arg): Correct documentation to
	say "argument is _no_ more constrained than the parameter".

gcc/testsuite/ChangeLog:

	PR c++/96229
	* g++.dg/cpp2a/concepts-class2.C: New test.
This commit is contained in:
Patrick Palka 2020-10-08 00:05:36 -04:00
parent 6caec77e3b
commit 6b1b5c255f
3 changed files with 19 additions and 7 deletions
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8
gcc/cp/parser.c
View File

@ -24044,10 +24044,6 @@ cp_parser_class_specifier_1 (cp_parser* parser)
= parser->in_unbraced_linkage_specification_p;
parser->in_unbraced_linkage_specification_p = false;
// Associate constraints with the type.
if (flag_concepts)
type = associate_classtype_constraints (type);
/* Start the class. */
if (nested_name_specifier_p)
{
@ -24815,6 +24811,10 @@ cp_parser_class_head (cp_parser* parser,
fixup_attribute_variants (type);
}
/* Associate constraints with the type. */
if (flag_concepts)
type = associate_classtype_constraints (type);
/* We will have entered the scope containing the class; the names of
base classes should be looked up in that context. For example:

7
gcc/cp/pt.c
View File

@ -8127,9 +8127,10 @@ canonicalize_expr_argument (tree arg, tsubst_flags_t complain)
return canon;
}
// A template declaration can be substituted for a constrained
// template template parameter only when the argument is more
// constrained than the parameter.
/* A template declaration can be substituted for a constrained
template template parameter only when the argument is no more
constrained than the parameter. */
static bool
is_compatible_template_arg (tree parm, tree arg)
{

11
gcc/testsuite/g++.dg/cpp2a/concepts-class2.C Normal file
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@ -0,0 +1,11 @@
// PR c++/96229
// { dg-do compile { target c++20 } }
template <class T> concept Int = requires { T{0}; };
template <template <Int> class P> struct X { };
template <Int> struct Y : X<Y> { };
struct Z { };
struct W { int i; };
Y<Z> z; // { dg-error "constraint" }
Y<W> w;