doc: Document 'this-package' and 'this-operating-system'.

* doc/guix.texi (package Reference): Document 'this-package'.
(operating-system Reference): Document 'this-operating-system'.
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Ludovic Courtès 2019-04-15 12:23:30 +02:00
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@ -5409,6 +5409,27 @@ automatically corrected.
@end table
@end deftp
@deffn {Scheme Syntax} this-package
When used in the @emph{lexical scope} of a package field definition, this
identifier resolves to the package being defined.
The example below shows how to add a package as a native input of itself when
cross-compiling:
@example
(package
(name "guile")
;; ...
;; When cross-compiled, Guile, for example, depends on
;; a native version of itself. Add it here.
(native-inputs (if (%current-target-system)
`(("self" ,this-package))
'())))
@end example
It is an error to refer to @code{this-package} outside a package definition.
@end deffn
@node origin Reference
@subsection @code{origin} Reference
@ -10592,6 +10613,27 @@ is that only @code{root} and members of the @code{wheel} group may use
@code{sudo}.
@end table
@deffn {Scheme Syntax} this-operating-system
When used in the @emph{lexical scope} of an operating system field definition,
this identifier resolves to the operating system being defined.
The example below shows how to refer to the operating system being defined in
the definition of the @code{label} field:
@example
(use-modules (gnu) (guix))
(operating-system
;; ...
(label (package-full-name
(operating-system-kernel this-operating-system))))
@end example
It is an error to refer to @code{this-operating-system} outside an operating
system definition.
@end deffn
@end deftp
@node File Systems