graph: Add "module" node type.

* guix/scripts/graph.scm (module-from-package)
(source-module-dependencies*): New procedures.
(%module-node-type): New variable.
(%node-types): Add it.
* guix/modules.scm (source-module-dependencies): Export.
* tests/graph.scm ("module graph"): New test.
* doc/guix.texi (Invoking guix graph): Document it.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 49b3dd10d7..2204285516 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -6997,6 +6997,15 @@ name instead of a package name, as in:
 @example
 guix graph -t derivation `guix system build -d my-config.scm`
 @end example
+
+@item module
+This is the graph of @dfn{package modules} (@pxref{Package Modules}).
+For example, the following command shows the graph for the package
+module that defines the @code{guile} package:
+
+@example
+guix graph -t module guile | dot -Tpdf > module-graph.pdf
+@end example
 @end table
 
 All the types above correspond to @emph{build-time dependencies}.  The