Add 'guix size'.

* guix/scripts/size.scm: New file.
* Makefile.am (MODULES): Add it.
  (SCM_TESTS): Add tests/size.scm.
* doc.am (SUBCOMMANDS): Add 'size'.
* po/guix/POTFILES.in: Add guix/scripts/size.scm.
* tests/size.scm: New file.
* doc/guix.texi (Packages with Multiple Outputs): Add xref to "Invoking guix
  size".
  (Invoking guix size): New node.
  (Invoking guix gc): Add index for "closure" and xref to the above.
* doc/contributing.texi (Submitting Patches): Use @enumerate for the check
  list.  Add item about 'guix size'.

2 files changed, 99 insertions, 7 deletions

diff --git a/doc/contributing.texi b/doc/contributing.texi
index 536f223da4b..7b16ea35392 100644
--- a/doc/contributing.texi
+++ b/doc/contributing.texi
@@ -203,14 +203,32 @@ standards, GNU Coding Standards}); you can check the commit history for
 examples.
 
 Before submitting a patch that adds or modifies a package definition,
-please run @code{guix lint @var{package}}, where @var{package} is the
+please run through this check list:
+
+@enumerate
+@item
+Run @code{guix lint @var{package}}, where @var{package} is the
 name of the new or modified package, and fix any errors it reports
-(@pxref{Invoking guix lint}).  In addition, please make sure the package
-builds on your platform, using @code{guix build @var{package}}.  You may
-also want to check that dependent package (if applicable) are not
-affected by the change; @code{guix refresh --list-dependent
+(@pxref{Invoking guix lint}).
+
+@item
+Make sure the package builds on your platform, using @code{guix build
+@var{package}}.
+
+@item
+Take a look at the profile reported by @command{guix size}
+(@pxref{Invoking guix size}).  This will allow you to notice references
+to other packages unwillingly retained.  It may also help determine
+whether to split the package (@pxref{Packages with Multiple Outputs}),
+and which optional dependencies should be used.
+
+@item
+For important changes, check that dependent package (if applicable) are
+not affected by the change; @code{guix refresh --list-dependent
 @var{package}} will help you do that (@pxref{Invoking guix refresh}).
 
+@end enumerate
+
 When posting a patch to the mailing list, use @samp{[PATCH] @dots{}} as a
 subject.  You may use your email client or the @command{git send-mail}
 command.
diff --git a/doc/guix.texi b/doc/guix.texi
index a93003d625b..a669464feb4 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -124,12 +124,13 @@ Defining Packages
 Utilities
 
 * Invoking guix build::         Building packages from the command line.
-* Invoking guix edit::
+* Invoking guix edit::          Editing package definitions.
 * Invoking guix download::      Downloading a file and printing its hash.
 * Invoking guix hash::          Computing the cryptographic hash of a file.
 * Invoking guix import::        Importing package definitions.
 * Invoking guix refresh::       Updating package definitions.
 * Invoking guix lint::          Finding errors in package definitions.
+* Invoking guix size::          Profiling disk usage.
 * Invoking guix environment::   Setting up development environments.
 * Invoking guix publish::       Sharing substitutes.
 
@@ -1495,7 +1496,8 @@ graphical user interfaces (GUIs).  The former depend solely on the C
 library, whereas the latter depend on Tcl/Tk and the underlying X
 libraries.  In this case, we leave the command-line tools in the default
 output, whereas the GUIs are in a separate output.  This allows users
-who do not need the GUIs to save space.
+who do not need the GUIs to save space.  The @command{guix size} command
+can help find out about such situations (@pxref{Invoking guix size}).
 
 There are several such multiple-output packages in the GNU distribution.
 Other conventional output names include @code{lib} for libraries and
@@ -1575,11 +1577,15 @@ as arguments.
 
 @item --requisites
 @itemx -R
+@cindex closure
 List the requisites of the store files passed as arguments.  Requisites
 include the store files themselves, their references, and the references
 of these, recursively.  In other words, the returned list is the
 @dfn{transitive closure} of the store files.
 
+@xref{Invoking guix size}, for a tool to profile the size of an
+element's closure.
+
 @end table
 
 Lastly, the following options allow you to check the integrity of the
@@ -3271,6 +3277,7 @@ programming interface of Guix in a convenient way.
 * Invoking guix import::        Importing package definitions.
 * Invoking guix refresh::       Updating package definitions.
 * Invoking guix lint::          Finding errors in package definitions.
+* Invoking guix size::          Profiling disk usage.
 * Invoking guix environment::   Setting up development environments.
 * Invoking guix publish::       Sharing substitutes.
 @end menu
@@ -3974,6 +3981,73 @@ and exit.
 
 @end table
 
+@node Invoking guix size
+@section Invoking @command{guix size}
+
+The @command{guix size} command helps package developers profile the
+disk usage of packages.  It is easy to overlook the impact of an
+additional dependency added to a package, or the impact of using a
+single output for a package that could easily be split (@pxref{Packages
+with Multiple Outputs}).  These are the typical issues that
+@command{guix size} can highlight.
+
+The command can be passed a package specification such as @code{gcc-4.8}
+or @code{guile:debug}, or a file name in the store.  Consider this
+example:
+
+@example
+$ guix size coreutils
+store item                               total    self
+/gnu/store/@dots{}-coreutils-8.23          70.0    13.9  19.8%
+/gnu/store/@dots{}-gmp-6.0.0a              55.3     2.5   3.6%
+/gnu/store/@dots{}-acl-2.2.52              53.7     0.5   0.7%
+/gnu/store/@dots{}-attr-2.4.46             53.2     0.3   0.5%
+/gnu/store/@dots{}-gcc-4.8.4-lib           52.9    15.7  22.4%
+/gnu/store/@dots{}-glibc-2.21              37.2    37.2  53.1%
+@end example
+
+@cindex closure
+The store items listed here constitute the @dfn{transitive closure} of
+Coreutils---i.e., Coreutils and all its dependencies, recursively---as
+would be returned by:
+
+@example
+$ guix gc -R /gnu/store/@dots{}-coreutils-8.23
+@end example
+
+Here the output shows 3 columns next to store items.  The first column,
+labeled ``total'', shows the size in mebibytes (MiB) of the closure of
+the store item---that is, its own size plus the size of all its
+dependencies.  The next column, labeled ``self'', shows the size of the
+item itself.  The last column shows the ratio of the item's size to the
+space occupied by all the items listed here.
+
+In this example, we see that the closure of Coreutils weighs in at
+70@tie{}MiB, half of which is taken by libc.  (That libc represents a
+large fraction of the closure is not a problem @i{per se} because it is
+always available on the system anyway.)
+
+When the package passed to @command{guix size} is available in the
+store, @command{guix size} queries the daemon to determine its
+dependencies, and measures its size in the store, similar to @command{du
+-ms --apparent-size} (@pxref{du invocation,,, coreutils, GNU
+Coreutils}).
+
+When the given package is @emph{not} in the store, @command{guix size}
+reports information based on information about the available substitutes
+(@pxref{Substitutes}).  This allows it to profile disk usage of store
+items that are not even on disk, only available remotely.
+
+A single option is available:
+
+@table @option
+
+@item --system=@var{system}
+@itemx -s @var{system}
+Consider packages for @var{system}---e.g., @code{x86_64-linux}.
+
+@end table
+
 @node Invoking guix environment
 @section Invoking @command{guix environment}