packages: Use origin file names as their input labels.

* guix/packages.scm (add-input-label): Rely on 'origin-actual-file-name' for
internal inputs labels.
* tests/packages.scm ("this-package-input, origin"): New test.
* doc/guix.texi (package Reference): Mention origin lookup for
‘lookup-package-input’ & co.
* gnu/packages/base.scm (tzdata)[inputs]: Reintroduce label.
* gnu/packages/tex.scm (texlive-hyphen-complete)[inputs]: Likewise.
(texlive-newverbs)[native-inputs]: Likewise.

Change-Id: I6ba5352b1b1b8ab810da3730b09cb9db61d6429c
Co-authored-by: Simon Tournier <zimon.toutoune@gmail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 57030102ca..9bf177a185 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -8061,8 +8061,8 @@ inputs.
 Look up @var{name} among @var{package}'s inputs (or native, propagated,
 or direct inputs).  Return it if found, @code{#f} otherwise.
 
-@var{name} is the name of a package depended on.  Here's how you might
-use it:
+@var{name} is the name of a package or the file name of an origin
+depended on.  Here's how you might use it:
 
 @lisp
 (use-modules (guix packages) (gnu packages base))
@@ -8073,6 +8073,10 @@ use it:
 
 In this example we obtain the @code{gmp} package that is among the
 direct inputs of @code{coreutils}.
+
+When looking up an origin, use the name that appears in the origin's
+@code{file-name} field or its default file name---e.g.,
+@code{"foo-1.2.tar.gz"}.
 @end deffn
 
 @cindex development inputs, of a package