guix package: Re-apply package transformation when upgrading.

* guix/scripts/package.scm (transaction-upgrade-entry)[upgrade]: Add
'transform' parameter.  Pass PKG through it.  Use
'manifest-entry-with-transformations'.
Call 'options->transformation' to get the transformation procedure.
* tests/guix-package.sh: Add 'guix package -u' test.
* tests/packages.scm ("transaction-upgrade-entry, transformation options preserved"):
New test.
* doc/guix.texi (Invoking guix package): Mention that transformations
are preserved across upgrades.
(Package Transformation Options): Likewise.

1 files changed, 27 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index da48c8a72d..a6260a12aa 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3101,6 +3101,29 @@ in the distribution currently installed.  To update your distribution,
 you should regularly run @command{guix pull} (@pxref{Invoking guix
 pull}).
 
+@cindex package transformations, upgrades
+When upgrading, package transformations that were originally applied
+when creating the profile are automatically re-applied (@pxref{Package
+Transformation Options}).  For example, assume you first installed Emacs
+from the tip of its development branch with:
+
+@example
+guix install emacs-next --with-branch=emacs-next=master
+@end example
+
+Next time you run @command{guix upgrade}, Guix will again pull the tip
+of the Emacs development branch and build @code{emacs-next} from that
+checkout.
+
+Note that transformation options such as @option{--with-branch} and
+@option{--with-source} depend on external state; it is up to you to
+ensure that they work as expected.  You can also discard a
+transformations that apply to a package by running:
+
+@example
+guix install @var{package}
+@end example
+
 @item --do-not-upgrade[=@var{regexp} @dots{}]
 When used together with the @option{--upgrade} option, do @emph{not}
 upgrade any packages whose name matches a @var{regexp}.  For example, to
@@ -9193,6 +9216,10 @@ This is a convenient way to create customized packages on the fly
 without having to type in the definitions of package variants
 (@pxref{Defining Packages}).
 
+Package transformation options are preserved across upgrades:
+@command{guix upgrade} attempts to apply transformation options
+initially used when creating the profile to the upgraded packages.
+
 @table @code
 
 @item --with-source=@var{source}