こんな感じで出力できた(｀・ω・´)

ast.txt

   ( 2 , 11 )
   - USR:  c:@aN
   - kind:  NAMESPACE
   B ( 4 , 11 )
   - USR:  c:@N@B
   - kind:  NAMESPACE
     A ( 6 , 7 )
     - USR:  c:@N@B@C@A
     - kind:  CLASS_DECL
     - type:  Record
        ( 7 , 2 )
       - USR:  c:
       - kind:  CXX_ACCESS_SPEC_DECL
       - c++ access type:  _CXXAccessSpecifier.Private
        ( 7 , 2 )
       - USR:  c:
       - kind:  CXX_ACCESS_SPEC_DECL
       - c++ access type:  _CXXAccessSpecifier.Private
       num_ ( 8 , 7 )
       - USR:  c:@N@B@C@A@FI@num_
       - kind:  FIELD_DECL
       - type:  Int
        ( 9 , 2 )
       - USR:  c:
       - kind:  CXX_ACCESS_SPEC_DECL
       - c++ access type:  _CXXAccessSpecifier.Public
        ( 9 , 2 )
       - USR:  c:
       - kind:  CXX_ACCESS_SPEC_DECL
       - c++ access type:  _CXXAccessSpecifier.Public
       A ( 10 , 3 )
       - USR:  c:@N@B@C@A@F@A#I#
       - kind:  CONSTRUCTOR
       - type:  FunctionProto
         arg ( 10 , 9 )
         - USR:  c:sample.cxx@101@N@B@C@A@F@A#I#@arg
         - kind:  PARM_DECL
         - type:  Int
         None ( 10 , 16 )
         - kind:  MEMBER_REF
         None ( 10 , 21 )
         - kind:  UNEXPOSED_EXPR
         - type:  Int
           None ( 10 , 21 )
           - kind:  DECL_REF_EXPR
           - type:  Int
         None ( 10 , 26 )
         - kind:  COMPOUND_STMT
       assign ( 12 , 8 )
       - USR:  c:@N@B@C@A@F@assign#I#
       - kind:  CXX_METHOD
       - type:  FunctionProto
         a ( 12 , 19 )
         - USR:  c:sample.cxx@140@N@B@C@A@F@assign#I#@a
         - kind:  PARM_DECL
         - type:  Int
         None ( 12 , 22 )
         - kind:  COMPOUND_STMT
           None ( 12 , 24 )
           - kind:  BINARY_OPERATOR
           - type:  Int
             None ( 12 , 24 )
             - kind:  MEMBER_REF_EXPR
             - type:  Int
             None ( 12 , 31 )
             - kind:  UNEXPOSED_EXPR
             - type:  Int
               None ( 12 , 31 )
               - kind:  DECL_REF_EXPR
               - type:  Int
     B ( 15 , 8 )
     - USR:  c:@N@B@S@B
     - kind:  STRUCT_DECL
     - type:  Record
     a_func ( 17 , 6 )
     - USR:  c:@N@B@F@a_func#$@N@B@C@A#I#
     - kind:  FUNCTION_DECL
     - type:  FunctionProto
       arg ( 17 , 15 )
       - USR:  c:sample.cxx@202@N@B@F@a_func#$@N@B@C@A#I#@arg
       - kind:  PARM_DECL
       - type:  Record
         None ( 17 , 13 )
         - kind:  TYPE_REF
         - type:  Record
         - type name:  ::B::A
       a ( 17 , 24 )
       - USR:  c:sample.cxx@209@N@B@F@a_func#$@N@B@C@A#I#@a
       - kind:  PARM_DECL
       - type:  Int
       None ( 17 , 27 )
       - kind:  COMPOUND_STMT

sample.cxx

namespace {} // spelling will be empty
namespace B {
class A {
 private:
  int num_;
 public:
  A(int arg) : num_(arg) {}
  void assign(int a) { num_ = a; }
}; // class A
struct B {};
void a_func(A arg, int a) {}
} // namespace B