On 1/27/22 13:06, Patrick Palka wrote:
On Thu, 27 Jan 2022, Patrick Palka wrote:
When deducing the type of a variable template specialization with a
constrained auto type, we might need the template arguments for
satisfaction in case the constraint is dependent.
It looks like templated static data members need similar treatment.
Here's a patch that handles both kinds of entities, what they have
in common is that they're templated and not at function scope
(bootstrap and regtesting in progress):
-- >8 --
Subject: [PATCH] c++: var tmpl w/ dependent constrained auto type [PR103341]
When deducing the type of a variable template specialization (or a
template static data member) with a constrained auto type, we might
need the template arguments during satisfaction from do_auto_deduction
in case the constraint is dependent.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk and perhaps 11?
OK for trunk. And for 11, if you make it conditional on flag_concepts.
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.
---
gcc/cp/decl.cc | 12 +++++++++++-
gcc/testsuite/g++.dg/cpp2a/concepts-class4.C | 12 ++++++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C | 13 +++++++++++++
3 files changed, 36 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-class4.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 10e6956117e..465f5620f2c 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -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 decls, do_auto_deduction obtains 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)
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-class4.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-class4.C
new file mode 100644
index 00000000000..9d694e758e0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-class4.C
@@ -0,0 +1,12 @@
+// PR c++/103341
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<class T>
+struct A {
+ static inline C<T> auto value = 0; // { dg-error "constraint" }
+};
+
+template struct A<int>; // { dg-bogus "" }
+template struct A<bool>; // { dg-message "required from here" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C
new file mode 100644
index 00000000000..e1802aca75f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ2.C
@@ -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" }
