How do I prevent "r 'library' or 'require' calls not declared" warnings when developing a package? -

I am developing a package that depends on the package foo , and in my package code Call the exported code from foo I have included the package name in the NAMESPACE in the Import (Af) declaration, and import Under: line description file However, I get the following warning when RCM check :

  r 'library 'Or' require 'call can not be declared Yes: 'foo'   
 What am I missing?  
 There is a similar question, but it does not discuss this specific warning.   
  ()  or  library (& lt ); Pkg & gt;) . The error message is a little confusing - it's telling you that you have placed the  requirement  or  library  in your code, but in reality (properly) those calls are not declared In your  DESCRIPTION  file.  
 If you intend to use code from those packages in your package, you should call this  library  /  call ; Rather, you need to declare them properly (and how you're using them) in your  DESCRIPTION  file.  
 Mostly, you want to import 'package and some, or all, for export functions / symbols available for your package. You can add such packages to your  DESCRIPTION  file in the  Import:  field - e.g.  
  Import: & lt; Pkg & gt;   
 And likewise, announce that you want to write  all  in the  NAMESPACE  file using the symbols exported from that package ,  
   Import   
 By doing this,  & lt; Pkg & gt; All functions in the namespace are automatically provided and therefore it is not necessary for  requirement  anywhere in your code.  
 In the context of a package, the main use of  is that which you want to make only conditionally, for example, suppose that you write the function that Handles a very specific conspiracy arrangement, which requires  foo , but  foo  is not required in your package otherwise, if you include code Want to do the conditional package  foo  Depending on it, you can write something in this form:  
  (if required ("foo")) {#do stuff}   
 And then you can include  foo  under  DESCRIPTION  instead of  sequence:   import: . Another example is a package that is not required by the users of your package.  
 In short: If you are importing packages to use only those packages exported to the namespace of that package, then you can send your package to  Library  or   is not needed anywhere in the code.  
 EDIT: In newer versions of R, the  RCM check  if you use , , warns it, And instead you suggest that you use  requireNamespace . In that case, you can follow the pattern:  
  ## Use the 'bar' function from the package 'Foo' (if required requires "name" ("foo", quietly = TRUE)) {foo :: Bar ()}