On Thu, 16 Sep 2021, Jason Merrill wrote:
> On 9/16/21 09:11, Patrick Palka wrote:
> > This fixes some issues with constrained variable templates:
> >
> > * Constraints aren't checked when explicitly specializing a variable
> > template
> > * Constraints aren't attached to a static data member template at
> > parse time
> > * Constraints aren't propagated when (partially) instantiating a
> > static data member template
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, and also tested on
> > cmcstl2 and range-v3, does this look OK for trunk and perhaps 11?
> >
> > PR c++/98486
> >
> > gcc/cp/ChangeLog:
> >
> > * decl.c (grokdeclarator): Set constraints on a static data
> > member template.
> > * pt.c (determine_specialization): Check constraints on a
> > variable template.
>
> These hunks are OK.
>
> > (tsubst_decl) <case VAR_DECL>: Propagate constraints on a
> > static data member template.
>
> Hmm, why is this necessary? I know we already do this for functions, but I
> don't remember why. Don't we check satisfaction for the most-general
> template?
Ah true, it looks like propagating constraints is not strictly necessary
for satisfaction for that reason..
But propagating them seems necessary for disambiguating constrained
overloads in a class template specialization:
template<class T>
struct A
{
void f() requires true; // #1
void f() requires false; // #2
};
template struct A<int>;
Without the propagation in tsubst_function_decl, during instantiation of
A<int> we complain from add_method that #2 cannot be overloaded with #1.
But I don't think this is a probem for static data member templates
since they can't be overloaded, so indeed there's no reason to propagate
constraints on them if we tweak get_normalized_constraints_from_decl.
How does the following look? Passes all the concepts tests so far, full
testing in progress:
-- >8 --
gcc/cp/ChangeLog:
* constraint.cc (get_normalized_constraints_from_decl): Look up
constraints using the most general template instead of the
specialization.
* decl.c (grokdeclarator): Set constraints on a static data
member template.
* pt.c (determine_specialization): Check constraints on a
variable template.
(tsubst_decl) <case VAR_DECL>: Propagate constraints on a
static data member template.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-var-templ1.C: New test.
* g++.dg/cpp2a/concepts-var-templ1a.C: New test.
* g++.dg/cpp2a/concepts-var-templ1b.C: New test.
---
gcc/cp/constraint.cc | 8 +++++---
gcc/cp/decl.c | 11 +++++++++++
gcc/cp/pt.c | 3 ++-
gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C | 9 +++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C | 15 +++++++++++++++
6 files changed, 56 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 1aaf1e27886..2896efdd7f2 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -918,20 +918,22 @@ get_normalized_constraints_from_decl (tree d, bool diag =
false)
tmpl = most_general_template (tmpl);
}
+ d = tmpl ? tmpl : decl;
+
/* If we're not diagnosing errors, use cached constraints, if any. */
if (!diag)
- if (tree *p = hash_map_safe_get (normalized_map, tmpl))
+ if (tree *p = hash_map_safe_get (normalized_map, d))
return *p;
tree norm = NULL_TREE;
- if (tree ci = get_constraints (decl))
+ if (tree ci = get_constraints (d))
{
push_access_scope_guard pas (decl);
norm = get_normalized_constraints_from_info (ci, tmpl, diag);
}
if (!diag)
- hash_map_safe_put<hm_ggc> (normalized_map, tmpl, norm);
+ hash_map_safe_put<hm_ggc> (normalized_map, d, norm);
return norm;
}
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index c0f1496636f..7beac79ec25 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -13980,6 +13980,17 @@ grokdeclarator (const cp_declarator *declarator,
if (declspecs->gnu_thread_keyword_p)
SET_DECL_GNU_TLS_P (decl);
}
+
+ /* Set the constraints on declaration. */
+ bool memtmpl = (processing_template_decl
+ > template_class_depth (current_class_type));
+ if (memtmpl)
+ {
+ tree tmpl_reqs
+ = TEMPLATE_PARMS_CONSTRAINTS (current_template_parms);
+ tree ci = build_constraints (tmpl_reqs, NULL_TREE);
+ set_constraints (decl, ci);
+ }
}
else
{
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 224dd9ebd2b..22c74da7935 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -2218,7 +2218,8 @@ determine_specialization (tree template_id,
targs = coerce_template_parms (parms, explicit_targs, fns,
tf_warning_or_error,
/*req_all*/true, /*use_defarg*/true);
- if (targs != error_mark_node)
+ if (targs != error_mark_node
+ && constraints_satisfied_p (fns, targs))
templates = tree_cons (targs, fns, templates);
}
else for (lkp_iterator iter (fns); iter; ++iter)
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C
new file mode 100644
index 00000000000..80b48ba3a3d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C
@@ -0,0 +1,9 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<C<int>> int v;
+
+template<> int v<int>;
+template<> int v<char>; // { dg-error "match" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C
new file mode 100644
index 00000000000..b12d37d8b7e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C
@@ -0,0 +1,14 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+struct A {
+ template<C<int>> static int v;
+};
+
+template<> int A::v<int>;
+template<> int A::v<char>; // { dg-error "match" }
+
+int x = A::v<int>;
+int y = A::v<char>; // { dg-error "invalid" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C
new file mode 100644
index 00000000000..37d7f0fc654
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C
@@ -0,0 +1,15 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<class T>
+struct A {
+ template<C<T>> static int v;
+};
+
+template<> template<> int A<int>::v<int>;
+template<> template<> int A<int>::v<char>; // { dg-error "match" }
+
+int x = A<int>::v<int>;
+int y = A<int>::v<char>; // { dg-error "invalid" }
--
2.33.0.363.g4c719308ce
