[pushed] c++: redeclare_class_template and ttps [PR110523]

[Patrick Palka via Gcc-patches]

Tested on x86_64-pc-linux-gnu, pushed to trunk as obvious.

-- >8 --

Now that we cache level-lowered ttps we can end up processing the same
ttp multiple times via (multiple calls to) redeclare_class_template, so
we can't assume a ttp's DECL_CONTEXT is initially empty.

        PR c++/110523

gcc/cp/ChangeLog:

        * pt.cc (redeclare_class_template): Relax the ttp DECL_CONTEXT
        assert, and downgrade it to a checking assert.

gcc/testsuite/ChangeLog:

        * g++.dg/template/ttp37.C: New test.
---
 gcc/cp/pt.cc                          |  3 ++-
 gcc/testsuite/g++.dg/template/ttp37.C | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/ttp37.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d7d774fd9e5..076f788281e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6388,7 +6388,8 @@ redeclare_class_template (tree type, tree parms, tree 
cons)
         DECL_CONTEXT of the template for which they are a parameter.  */
       if (TREE_CODE (parm) == TEMPLATE_DECL)
        {
-         gcc_assert (DECL_CONTEXT (parm) == NULL_TREE);
+         gcc_checking_assert (DECL_CONTEXT (parm) == NULL_TREE
+                              || DECL_CONTEXT (parm) == tmpl);
          DECL_CONTEXT (parm) = tmpl;
        }
     }
diff --git a/gcc/testsuite/g++.dg/template/ttp37.C 
b/gcc/testsuite/g++.dg/template/ttp37.C
new file mode 100644
index 00000000000..c5f4e99c20a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp37.C
@@ -0,0 +1,15 @@
+// PR c++/110523
+
+template<template<class> class>
+class basic_json;
+
+template<class>
+struct json_pointer {
+  template<template<class> class>
+  friend class basic_json;
+};
+
+template struct json_pointer<int>;
+template struct json_pointer<char>;
+template struct json_pointer<long>;
+template struct json_pointer<void>;
-- 
2.41.0.327.gaa9166bcc0