c++ modules: partial variable template specializations [PR106826]

With partial variable template specializations, it looks like we
stream the VAR_DECL (i.e. the DECL_TEMPLATE_RESULT of the corresponding
TEMPLATE_DECL) since process_partial_specialization adds it to the
specializations table, but we end up never streaming the corresponding
TEMPLATE_DECL itself that's reachable only from the primary template's
DECL_TEMPLATE_SPECIALIZATIONS list, which leads to this list being
incomplete on stream-in.

The modules machinery already has special logic for streaming partial
specializations of class templates; this patch attempts to generalize
it to handle those of variable templates as well.

	PR c++/106826

gcc/cp/ChangeLog:

	* module.cc (trees_out::decl_value): Use get_template_info in
	the MK_partial case to handle both VAR_DECL and TYPE_DECL.
	(trees_out::key_mergeable): Likewise.
	(trees_in::key_mergeable): Likewise.
	(has_definition): Consider DECL_INITIAL of a partial variable
	template specialization.
	(depset::hash::make_dependency): Handle partial variable template
	specializations too.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/partial-2_a.C: New test.
	* g++.dg/modules/partial-2_b.C: New test.

2 files changed, 64 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/modules/partial-2_a.C b/gcc/testsuite/g++.dg/modules/partial-2_a.C
new file mode 100644
index 0000000..2681bb5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/partial-2_a.C
@@ -0,0 +1,43 @@
+// PR c++/106826
+// { dg-additional-options -fmodules-ts }
+// { dg-module-cmi pr106826 }
+export module pr106826;
+
+template<class T> constexpr bool is_reference_v = false;
+template<class T> constexpr bool is_reference_v<T&> = true;
+template<class T> constexpr bool is_reference_v<T&&> = true;
+
+struct A {
+  template<class T> static constexpr bool is_reference_v = false;
+};
+
+template<class T> constexpr bool A::is_reference_v<T&> = true;
+template<class T> constexpr bool A::is_reference_v<T&&> = true;
+
+#if __cpp_concepts
+namespace concepts {
+  template<class T> bool is_reference_v;
+
+  template<class T> requires __is_same(T, T&)
+  constexpr bool is_reference_v<T> = true;
+
+  template<class T> requires __is_same(T, T&&) && (!__is_same(T, T&))
+  constexpr bool is_reference_v<T> = true;
+
+  template<class T> requires (!__is_same(T, T&)) && (!__is_same(T, T&&))
+  constexpr bool is_reference_v<T> = false;
+
+  struct A {
+    template<class T> static bool is_reference_v;
+  };
+
+  template<class T> requires __is_same(T, T&)
+  constexpr bool A::is_reference_v<T> = true;
+
+  template<class T> requires __is_same(T, T&&) && (!__is_same(T, T&))
+  constexpr bool A::is_reference_v<T> = true;
+
+  template<class T> requires (!__is_same(T, T&)) && (!__is_same(T, T&&))
+  constexpr bool A::is_reference_v<T> = false;
+}
+#endif
diff --git a/gcc/testsuite/g++.dg/modules/partial-2_b.C b/gcc/testsuite/g++.dg/modules/partial-2_b.C
new file mode 100644
index 0000000..0af41ef
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/partial-2_b.C
@@ -0,0 +1,21 @@
+// PR c++/106826
+// { dg-additional-options -fmodules-ts }
+module pr106826;
+
+static_assert(is_reference_v<int&>);
+static_assert(is_reference_v<int&&>);
+static_assert(!is_reference_v<int>);
+
+static_assert(A::is_reference_v<long&>);
+static_assert(A::is_reference_v<long&&>);
+static_assert(!A::is_reference_v<long>);
+
+#if __cpp_concepts
+static_assert(concepts::is_reference_v<char&>);
+static_assert(concepts::is_reference_v<char&&>);
+static_assert(!concepts::is_reference_v<char>);
+
+static_assert(concepts::A::is_reference_v<bool&>);
+static_assert(concepts::A::is_reference_v<bool&&>);
+static_assert(!concepts::A::is_reference_v<bool>);
+#endif