ICE when calling templated function from extern (C++) templated function?

[Elronnd via D.gnu]

Here's a minimal example:

  void r(T...)(T args) {}
  extern (C++) {
          void s(T...)(T args) { r(args); }
  }

  void main() {
          s(0);
  }

Traceback from GDC:

  cc1d: ../../gcc-6.3.0/gcc/d/dfrontend/cppmangle.c:185: void 
CppMangleVisitor::source_name(Dsymbol*, bool): Assertion `t' 
failed.
  minim.d: In function ‘D main’:
  minim.d:9:2: internal compiler error: Aborted
    s(0);
    ^
  0xb91c3f crash_signal
        ../../gcc-6.3.0/gcc/toplev.c:333
  0x5f4f26 CppMangleVisitor::source_name(Dsymbol*, bool)
        ../../gcc-6.3.0/gcc/d/dfrontend/cppmangle.c:185
  0x5f0b82 CppMangleVisitor::mangle_function(FuncDeclaration*)
        ../../gcc-6.3.0/gcc/d/dfrontend/cppmangle.c:462
  0x5f0b82 CppMangleVisitor::mangleOf(Dsymbol*)
        ../../gcc-6.3.0/gcc/d/dfrontend/cppmangle.c:575
  0x5f0b82 toCppMangle(Dsymbol*)
        ../../gcc-6.3.0/gcc/d/dfrontend/cppmangle.c:910
  0x67ba17 Mangler::visit(Declaration*)
        ../../gcc-6.3.0/gcc/d/dfrontend/mangle.c:421
  0x67a2f8 mangleExact(FuncDeclaration*)
        ../../gcc-6.3.0/gcc/d/dfrontend/mangle.c:877
  0x6ed183 get_symbol_decl(Declaration*)
        ../../gcc-6.3.0/gcc/d/d-decls.cc:164
  0x72ab78 ExprVisitor::visit(VarExp*)
        ../../gcc-6.3.0/gcc/d/expr.cc:2062
  0x7298ef build_expr(Expression*, bool)
        ../../gcc-6.3.0/gcc/d/expr.cc:2851
  0x72b759 ExprVisitor::visit(CallExp*)
        ../../gcc-6.3.0/gcc/d/expr.cc:1633
  0x7298ef build_expr(Expression*, bool)
        ../../gcc-6.3.0/gcc/d/expr.cc:2851
  0x729a5f build_expr_dtor(Expression*)
        ../../gcc-6.3.0/gcc/d/expr.cc:2895
  0x731d7c IRVisitor::visit(ExpStatement*)
        ../../gcc-6.3.0/gcc/d/toir.cc:649
  0x731bf8 IRVisitor::visit(CompoundStatement*)
        ../../gcc-6.3.0/gcc/d/toir.cc:665
  0x731b95 build_ir(FuncDeclaration*)
        ../../gcc-6.3.0/gcc/d/toir.cc:1037
  0x706d84 FuncDeclaration::toObjFile()
        ../../gcc-6.3.0/gcc/d/d-objfile.cc:1359
  0x7083a4 Module::genobjfile(bool)
        ../../gcc-6.3.0/gcc/d/d-objfile.cc:1465
  0x6e7f22 d_parse_file()
        ../../gcc-6.3.0/gcc/d/d-lang.cc:1215
  Please submit a full bug report,
  with preprocessed source if appropriate.
  Please include the complete backtrace with any bug report.
  See <http://gcc.gnu.org/bugs.html> for instructions.