code: Symbol resolveSelfContaining(DiagnosticPosition pos,
                                   Env<AttrContext> env,
                                   Symbol member,
                                   boolean isSuperCall) {
          Symbol sym = resolveSelfContainingInternal(env, member, isSuperCall);
          if (sym == null) {
              log.error(pos, "encl.class.required", member);
              return syms.errSymbol;
          } else {
              return accessBase(sym, pos, env.enclClass.sym.type, sym.name, true);
          }
      }
docs: Resolve `c.this' for an enclosing class c that contains the
  named member.
  @param pos           The position to use for error reporting.
  @param env           The environment current at the expression.
  @param member        The member that must be contained in the result.