[pushed] c++: requires and using-decl [PR113498]

[Jason Merrill]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- 8< --

get_template_info was crashing because it assumed that any decl with
DECL_LANG_SPECIFIC could use DECL_TEMPLATE_INFO.  It's more complicated than
that.

        PR c++/113498

gcc/cp/ChangeLog:

        * pt.cc (decl_template_info): New fn.
        (get_template_info): Use it.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/concepts-using4.C: New test.
---
 gcc/cp/pt.cc                                 | 30 ++++++++++++++++++--
 gcc/testsuite/g++.dg/cpp2a/concepts-using4.C | 24 ++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-using4.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fbbca469219..74013533b0f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -339,6 +339,32 @@ build_template_info (tree template_decl, tree 
template_args)
   return result;
 }
 
+/* DECL_TEMPLATE_INFO, if applicable, or NULL_TREE.  */
+
+static tree
+decl_template_info (const_tree decl)
+{
+  /* This needs to match template_info_decl_check.  */
+  if (DECL_LANG_SPECIFIC (decl))
+    switch (TREE_CODE (decl))
+      {
+      case FUNCTION_DECL:
+       if (DECL_THUNK_P (decl))
+         break;
+       gcc_fallthrough ();
+      case VAR_DECL:
+      case FIELD_DECL:
+      case TYPE_DECL:
+      case CONCEPT_DECL:
+      case TEMPLATE_DECL:
+       return DECL_TEMPLATE_INFO (decl);
+
+      default:
+       break;
+      }
+  return NULL_TREE;
+}
+
 /* Return the template info node corresponding to T, whatever T is.  */
 
 tree
@@ -353,8 +379,8 @@ get_template_info (const_tree t)
       || TREE_CODE (t) == PARM_DECL)
     return NULL;
 
-  if (DECL_P (t) && DECL_LANG_SPECIFIC (t))
-    tinfo = DECL_TEMPLATE_INFO (t);
+  if (DECL_P (t))
+    tinfo = decl_template_info (t);
 
   if (!tinfo && DECL_IMPLICIT_TYPEDEF_P (t))
     t = TREE_TYPE (t);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-using4.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-using4.C
new file mode 100644
index 00000000000..a39a7c0a8a3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-using4.C
@@ -0,0 +1,24 @@
+// PR c++/113498
+// { dg-do compile { target c++20 } }
+
+template<int d>
+struct S_Base
+{
+    static constexpr int D = d;
+};
+
+template<int d>
+struct S : public S_Base<d>
+{
+    using S_Base<d>::D;
+    constexpr void f() const
+        requires(D > 0) {}
+
+};
+
+int main(int, char**)
+{
+    S<1> s;
+    s.f();
+    return 0;
+}

base-commit: 631a922e5c8578a1c878b69f1651d482b661ef4a
-- 
2.39.3