c++: recognize in-class var tmpl partial spec [PR71954]

This makes us recognize member variable template partial specializations
defined directly inside the class body.  It seems we mainly just need to
call check_explicit_specialization when we see a static TEMPLATE_ID_EXPR
data member, which sets SET_DECL_TEMPLATE_SPECIALIZATION for us and which
we otherwise don't call (for the out-of-class case we call it from
grokvardecl).

We also need to make finish_member_template_decl return NULL_TREE for
such partial specializations, matching its behavior for class template
partial specializations, so that later we don't try to register it as a
separate member declaration.

	PR c++/71954

gcc/cp/ChangeLog:

	* decl.cc (grokdeclarator): Pass 'dname' instead of
	'unqualified_id' as the name when building the VAR_DECL for a
	static data member.  Call check_explicit_specialization for a
	TEMPLATE_ID_EXPR such member.
	* pt.cc (finish_member_template_decl): Return NULL_TREE
	instead of 'decl' when DECL_TEMPLATE_SPECIALIZATION is not
	set.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/var-templ84.C: New test.
	* g++.dg/cpp1y/var-templ84a.C: New test.

4 files changed, 42 insertions, 2 deletions

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 792ab33..e21e015 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -14439,7 +14439,16 @@ grokdeclarator (const cp_declarator *declarator,
 		/* C++ allows static class members.  All other work
 		   for this is done by grokfield.  */
 		decl = build_lang_decl_loc (id_loc, VAR_DECL,
-					    unqualified_id, type);
+					    dname, type);
+		if (unqualified_id
+		    && TREE_CODE (unqualified_id) == TEMPLATE_ID_EXPR)
+		  {
+		    decl = check_explicit_specialization (unqualified_id, decl,
+							  template_count,
+							  concept_p * 8);
+		    if (decl == error_mark_node)
+		      return error_mark_node;
+		  }
 		set_linkage_for_static_data_member (decl);
 		if (concept_p)
 		  error_at (declspecs->locations[ds_concept],
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2706fa6..a4809f0 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -314,7 +314,7 @@ finish_member_template_decl (tree decl)
 	  return DECL_TI_TEMPLATE (decl);
 	}
       else
-	return decl;
+	return NULL_TREE;
     }
   else
     error_at (DECL_SOURCE_LOCATION (decl),
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ84.C b/gcc/testsuite/g++.dg/cpp1y/var-templ84.C
new file mode 100644
index 0000000..39c2a0d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ84.C
@@ -0,0 +1,12 @@
+// PR c++/71954
+// { dg-do compile { target c++14 } }
+
+struct A {
+  template<class T> static const int var = 0;
+  template<class T> static const int var<T*> = 1;
+  template<class T> static const int var<const T*> = 2;
+};
+
+static_assert(A::var<int> == 0, "");
+static_assert(A::var<int*> == 1, "");
+static_assert(A::var<const int*> == 2, "");
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ84a.C b/gcc/testsuite/g++.dg/cpp1y/var-templ84a.C
new file mode 100644
index 0000000..4aa3a2a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ84a.C
@@ -0,0 +1,19 @@
+// PR c++/71954
+// A version of var-templ84.C where the partial specializations depend on
+// outer template parameters.
+// { dg-do compile { target c++14 } }
+
+template<class T>
+struct A {
+  template<class U, class V> static const int var = 0;
+  template<class U> static const int var<U*, T> = 1;
+  template<class U> static const int var<const U*, T> = 2;
+};
+
+static_assert(A<int>::var<int, int> == 0, "");
+static_assert(A<int>::var<int*, int> == 1, "");
+static_assert(A<int>::var<const int*, int> == 2, "");
+
+static_assert(A<int>::var<int, char> == 0, "");
+static_assert(A<int>::var<int*, char> == 0, "");
+static_assert(A<int>::var<const int*, char> == 0, "");