guix-package: Add `--list-installed'.

* guix-package.in (show-help, %options): Add `--list-installed'.
  (guix-package): Move main body to...
  [process-actions]: ... here.  New internal procedure.
  [process-query]: New procedure.
* tests/guix-package.sh: Add tests for `--list-installed'.
* doc/guix.texi (Invoking guix-package): Document it.

1 files changed, 18 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 637265d873..a93510ee23 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -239,7 +239,25 @@ useful to distribution developers.
 
 @end table
 
+In addition to these actions @command{guix-package} supports the
+following options to query the current state of a profile, or the
+availability of packages:
 
+@table @option
+
+@item --list-installed[=@var{regexp}]
+@itemx -I [@var{regexp}]
+List currently installed packages in the specified profile.  When
+@var{regexp} is specified, list only installed packages whose name
+matches @var{regexp}.
+
+For each installed package, print the following items, separated by
+tabs: the package name, its version string, the part of the package that
+is installed (for instance, @code{out} for the default output,
+@code{include} for its headers, etc.), and the path of this package in
+the store.
+
+@end table