guix package: Add '--allow-collisions'.

Fixes <https://bugs.gnu.org/30830>.
Suggested by Ricardo Wurmus <rekado@elephly.net>.

* guix/scripts/package.scm (build-and-use-profile): Add
 #:allow-collisions? and pass it to 'profile-derivation'.
(show-help, %options): Add '--allow-collisions'.
(manifest-action, process-actions): Pass #:allow-collisions? to
'build-and-use-profile'.
* tests/guix-package.sh: Add collision test.
* doc/guix.texi (Invoking guix package): Document '--allow-collisions'.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 25c08b9f06..4eac281a82 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2039,6 +2039,16 @@ variable, even though, taken individually, neither @file{foo} nor
 @itemx -p @var{profile}
 Use @var{profile} instead of the user's default profile.
 
+@cindex collisions, in a profile
+@cindex colliding packages in profiles
+@cindex profile collisions
+@item --allow-collisions
+Allow colliding packages in the new profile.  Use at your own risk!
+
+By default, @command{guix package} reports as an error @dfn{collisions}
+in the profile.  Collisions happen when two or more different versions
+or variants of a given package end up in the profile.
+
 @item --verbose
 Produce verbose output.  In particular, emit the build log of the
 environment on the standard error port.