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c++: var tmpl w/ dependent constrained auto type [PR103341] 

When deducing the type of a variable template (or templated static data
member) with a constrained auto type, we might need its template
arguments for satisfaction since the constraint could depend on them.

	PR c++/103341

gcc/cp/ChangeLog:

	* decl.cc (cp_finish_decl): Pass the template arguments of a
	variable template specialization or a templated static data
	member to do_auto_deduction when the auto is constrained.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-class4.C: New test.
	* g++.dg/cpp2a/concepts-var-templ2.C: New test.
This commit is contained in:
Patrick Palka 2022-01-28 08:18:28 -05:00
parent 9ec306582f
commit e272cf95ba
3 changed files with 35 additions and 1 deletions
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12
gcc/cp/decl.cc
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@ -7958,9 +7958,19 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
enum auto_deduction_context adc = adc_variable_type;
if (VAR_P (decl) && DECL_DECOMPOSITION_P (decl))
adc = adc_decomp_type;
tree outer_targs = NULL_TREE;
if (PLACEHOLDER_TYPE_CONSTRAINTS_INFO (auto_node)
&& VAR_P (decl)
&& DECL_LANG_SPECIFIC (decl)
&& DECL_TEMPLATE_INFO (decl)
&& !DECL_FUNCTION_SCOPE_P (decl))
/* The outer template arguments might be needed for satisfaction.
(For function scope variables, do_auto_deduction will obtain the
outer template arguments from current_function_decl.) */
outer_targs = DECL_TI_ARGS (decl);
type = TREE_TYPE (decl) = do_auto_deduction (type, d_init, auto_node,
tf_warning_or_error, adc,
NULL_TREE, flags);
outer_targs, flags);
if (type == error_mark_node)
return;
if (TREE_CODE (type) == FUNCTION_TYPE)

11
gcc/testsuite/g++.dg/cpp2a/concepts-class4.C Normal file
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@ -0,0 +1,11 @@
// PR c++/103341
// { dg-do compile { target c++20 } }
template<class T, class U> concept same_as = __is_same(T, U);
template<class T>
struct A {
static inline same_as<T> auto value = 0; // { dg-error "constraint" }
};
template struct A<int>; // { dg-bogus "" }
template struct A<bool>; // { dg-message "required from here" }

13
gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C Normal file
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@ -0,0 +1,13 @@
// PR c++/103341
// { dg-do compile { target c++20 } }
template<class T, class U> concept same_as = __is_same(T, U);
template<class T> same_as<T> auto v1a = 1;
template<class T> same_as<T> auto v1b = T();
template<class T> same_as<T*> auto v2a = 1; // { dg-error "constraints" }
template<class T> same_as<T*> auto v2b = T(); // { dg-error "constraints" }
template int v1a<int>;
template int v1b<int>;
template int v2a<int>; // { dg-message "required from here" }
template int v2b<int>; // { dg-message "required from here" }