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c++: elaborated-type-spec in requires-expr [PR101677]

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We were failing to declare class S in the global namespace because we were
treating the requires-expression parameter scope as a normal block scope, so
the implicit declaration went there.

It seems to me that the requires parameter scope is more like a function
parameter scope (not least in the use of the word "parameter"), so let's
change the scope kind.  But then we need to adjust the prohibition on
placeholders declaring implicit template parameters.

	PR c++/101677

gcc/cp/ChangeLog:

	* name-lookup.h (struct cp_binding_level): Add requires_expression
	bit-field.
	* parser.cc (cp_parser_requires_expression): Set it.
	(synthesize_implicit_template_parm): Check it.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-pr67178.C: Adjust error.
	* g++.dg/cpp2a/concepts-requires28.C: New test.
This commit is contained in:
Jason Merrill 2022-03-27 22:31:51 -04:00
parent 5c8d22b00a
commit 1de6612d99
4 changed files with 21 additions and 4 deletions
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5
gcc/cp/name-lookup.h
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@ -309,7 +309,10 @@ struct GTY(()) cp_binding_level {
/* true for SK_FUNCTION_PARMS of immediate functions. */
unsigned immediate_fn_ctx_p : 1;
/* 22 bits left to fill a 32-bit word. */
/* True for SK_FUNCTION_PARMS of a requires-expression. */
unsigned requires_expression: 1;
/* 21 bits left to fill a 32-bit word. */
};
/* The binding level currently in effect. */

5
gcc/cp/parser.cc
View File

@ -29964,7 +29964,8 @@ cp_parser_requires_expression (cp_parser *parser)
scope_sentinel ()
{
++cp_unevaluated_operand;
begin_scope (sk_block, NULL_TREE);
begin_scope (sk_function_parms, NULL_TREE);
current_binding_level->requires_expression = true;
}
~scope_sentinel ()
@ -48082,7 +48083,7 @@ static tree
synthesize_implicit_template_parm (cp_parser *parser, tree constr)
{
/* A requires-clause is not a function and cannot have placeholders. */
if (current_binding_level->kind == sk_block)
if (current_binding_level->requires_expression)
{
error ("placeholder type not allowed in this context");
return error_mark_node;

2
gcc/testsuite/g++.dg/cpp2a/concepts-pr67178.C
View File

@ -12,7 +12,7 @@ concept C0 = requires (auto x) { // { dg-error "placeholder type" }
template<typename T>
concept C1 = requires (C1 auto x) { // { dg-error "not been declared|placeholder|two or more|in requirements" }
x; // { dg-error "not declared" }
{ x } -> c; // { dg-message "is invalid" }
{ x } -> c; // { dg-message "is invalid|not declared" }
};
template<typename T>

13
gcc/testsuite/g++.dg/cpp2a/concepts-requires28.C Normal file
View File

@ -0,0 +1,13 @@
// PR c++/101677
// { dg-do compile { target c++20 } }
template<class T>
concept C_bug_with_forward_decl = requires(T& t){
t.template f<class S>();
};
struct good {
template<class T> void f() {}
};
static_assert(C_bug_with_forward_decl<good>);