Toggle diff (189 lines)
diff --git a/doc/guix.texi b/doc/guix.texi
index 2ed545847b..e174e13887 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -10021,6 +10021,12 @@ In this example we see that the combination of the four packages takes
102.3@tie{}MiB in total, which is much less than the sum of each closure
since they have a lot of dependencies in common.
+When looking at the profile returned by @command{guix size}, you may
+find yourself wondering why a given package shows up in the profile at
+all. To understand it, you can use @command{guix graph --path -t
+references} to display the shortest path between the two packages
+(@pxref{Invoking guix graph}).
+
The available options are:
@table @option
@@ -10081,8 +10087,9 @@ directly to the @command{dot} command of Graphviz. It can also emit an
HTML page with embedded JavaScript code to display a ``chord diagram''
in a Web browser, using the @uref{https://d3js.org/, d3.js} library, or
emit Cypher queries to construct a graph in a graph database supporting
-the @uref{https://www.opencypher.org/, openCypher} query language.
-The general syntax is:
+the @uref{https://www.opencypher.org/, openCypher} query language. With
+@option{--path}, it simply displays the shortest path between two
+packages. The general syntax is:
@example
guix graph @var{options} @var{package}@dots{}
@@ -10228,6 +10235,29 @@ collected.
@end table
+@cindex shortest path, between packages
+Often, the graph of the package you are interested in does not fit on
+your screen, and anyway all you want to know is @emph{why} that package
+actually depends on some seemingly unrelated package. The
+@option{--path} option instructs @command{guix graph} to display the
+shortest path between two packages (or derivations, or store items,
+etc.):
+
+@example
+$ guix graph --path emacs libunistring
+emacs@@26.3
+mailutils@@3.9
+libunistring@@0.9.10
+$ guix graph --path -t derivation emacs libunistring
+/gnu/store/@dots{}-emacs-26.3.drv
+/gnu/store/@dots{}-mailutils-3.9.drv
+/gnu/store/@dots{}-libunistring-0.9.10.drv
+$ guix graph --path -t references emacs libunistring
+/gnu/store/@dots{}-emacs-26.3
+/gnu/store/@dots{}-libidn2-2.2.0
+/gnu/store/@dots{}-libunistring-0.9.10
+@end example
+
The available options are the following:
@table @option
@@ -10248,6 +10278,20 @@ List the supported graph backends.
Currently, the available backends are Graphviz and d3.js.
+@item --path
+Display the shortest path between two nodes of the type specified by
+@option{--type}. The example below shows the shortest path between
+@code{libreoffice} and @code{llvm} according to the references of
+@code{libreoffice}:
+
+@example
+$ guix graph --path -t references libreoffice llvm
+/gnu/store/@dots{}-libreoffice-6.4.2.2
+/gnu/store/@dots{}-libepoxy-1.5.4
+/gnu/store/@dots{}-mesa-19.3.4
+/gnu/store/@dots{}-llvm-9.0.1
+@end example
+
@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.
diff --git a/guix/scripts/graph.scm b/guix/scripts/graph.scm
index d69dace14f..1d5db3b3cb 100644
--- a/guix/scripts/graph.scm
+++ b/guix/scripts/graph.scm
@@ -455,6 +455,29 @@ package modules, while attempting to retain user package modules."
(graph-backend-description backend)))
%graph-backends))
+
+;;;
+;;; Displaying a path.
+;;;
+
+(define (display-path node1 node2 type)
+ "Display the shortest path from NODE1 to NODE2, of TYPE."
+ (mlet %store-monad ((path (shortest-path node1 node2 type)))
+ (define node-label
+ (let ((label (node-type-label type)))
+ ;; Special-case derivations and store items to print them in full,
+ ;; contrary to what their 'node-type-label' normally does.
+ (match-lambda
+ ((? derivation? drv) (derivation-file-name drv))
+ ((? string? str) str)
+ (node (label node)))))
+
+ (if path
+ (format #t "~{~a~%~}" (map node-label path))
+ (leave (G_ "no path from '~a' to '~a'~%")
+ (node-label node1) (node-label node2)))
+ (return #t)))
+
;;;
;;; Command-line options.
@@ -465,6 +488,9 @@ package modules, while attempting to retain user package modules."
(lambda (opt name arg result)
(alist-cons 'node-type (lookup-node-type arg)
result)))
+ (option '("path") #f #f
+ (lambda (opt name arg result)
+ (alist-cons 'path? #t result)))
(option '("list-types") #f #f
(lambda (opt name arg result)
(list-node-types)
@@ -510,6 +536,8 @@ Emit a representation of the dependency graph of PACKAGE...\n"))
-t, --type=TYPE represent nodes of the given TYPE"))
(display (G_ "
--list-types list the available graph types"))
+ (display (G_ "
+ --path display the shortest path between the given nodes"))
(display (G_ "
-e, --expression=EXPR consider the package EXPR evaluates to"))
(display (G_ "
@@ -566,11 +594,19 @@ Emit a representation of the dependency graph of PACKAGE...\n"))
(mlet %store-monad ((_ (set-grafting #f))
(nodes (mapm %store-monad
(node-type-convert type)
- items)))
- (export-graph (concatenate nodes)
- (current-output-port)
- #:node-type type
- #:backend backend))
+ (reverse items))))
+ (if (assoc-ref opts 'path?)
+ (match nodes
+ (((node1 _ ...) (node2 _ ...))
+ (display-path node1 node2 type))
+ (_
+ (leave (G_ "'--path' option requires exactly two \
+nodes (given ~a)~%")
+ (length nodes))))
+ (export-graph (concatenate nodes)
+ (current-output-port)
+ #:node-type type
+ #:backend backend)))
#:system (assq-ref opts 'system)))))
#t)
diff --git a/tests/guix-graph.sh b/tests/guix-graph.sh
index 4c37b61b38..ccb4933c88 100644
--- a/tests/guix-graph.sh
+++ b/tests/guix-graph.sh
@@ -1,5 +1,5 @@
# GNU Guix --- Functional package management for GNU
-# Copyright © 2015, 2016, 2019 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2015, 2016, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
# Copyright © 2019 Simon Tournier <zimon.toutoune@gmail.com>
#
# This file is part of GNU Guix.
@@ -82,3 +82,17 @@ then false; else true; fi
# Try --load-path
guix graph -L $module_dir dummy | grep 'label = "dummy'
+
+# Displaying shortest paths (or lack thereof).
+if guix graph --path emacs vim; then false; else true; fi
+
+path="\
+emacs
+gnutls
+guile
+libffi"
+test "`guix graph --path emacs libffi | cut -d '@' -f1`" = "$path"
+
+# At the derivation level, there's a direct path because libffi is propagated
+# via gtk+.
+test "`guix graph --path -t derivation emacs libffi | wc -l`" -ge 2
--
2.26.2
