code: public static Matcher<? super MethodInvocationTree> sameArgument(
        final int index1, final int index2) {
      return new Matcher<MethodInvocationTree>() {
        @Override
        public boolean matches(MethodInvocationTree methodInvocationTree, VisitorState state) {
          List<? extends ExpressionTree> args = methodInvocationTree.getArguments();
          return ASTHelpers.sameVariable(args.get(index1), args.get(index2));
        }
      };
    }
docs: Matches a {@link MethodInvocation} when the arguments at the two given indices are both the
  same variable, as determined by {@link ASTHelpers#sameVariable}.
  
  @param index1 the index of the first actual parameter to test
  @param index2 the index of the second actual parameter to test
  @throws IndexOutOfBoundsException if the given indices are invalid