use-package packages-to-use &optional package → t

packages-to-use — a designator for a list of package designators. The KEYWORD package may not be supplied.

package — a package designator. The default is the current package. The package cannot be the KEYWORD package.

use-package causes package to inherit all the external symbols of packages-to-use. The inherited symbols become accessible as internal symbols of package.

Packages-to-use are added to the use list of package if they are not there already. All external symbols in packages-to-use become accessible in package as internal symbols. use-package does not cause any new symbols to be present in package but only makes them accessible by inheritance.

use-package checks for name conflicts between the newly imported symbols and those already accessible in package. A name conflict in use-package between two external symbols inherited by package from packages-to-use may be resolved in favor of either symbol by importing one of them into package and making it a shadowing symbol.

(export (intern "LAND-FILL" (make-package 'trash)) 'trash) → T 
(find-symbol "LAND-FILL" (make-package 'temp)) → NIL, NIL 
(package-use-list 'temp) → (#<PACKAGE "TEMP">) 
(use-package 'trash 'temp) → T 
(package-use-list 'temp) → (#<PACKAGE "TEMP"> #<PACKAGE "TRASH">) 
(find-symbol "LAND-FILL" 'temp) → TRASH:LAND-FILL, :INHERITED

The use list of package may be modified.

unuse-package, package-use-list, Section 11.1 (Package Concepts)

It is permissible for a package P₁ to use a package P₂ even if P₂ already uses P₁. The using of packages is not transitive, so no problem results from the apparent circularity.