graph: Support package transformation options.

* guix/scripts/graph.scm (%options): Append %TRANSFORMATION-OPTIONS.
(show-help): Call 'show-transformation-options-help'.
(guix-graph): Call 'options->transformation' and use it.
* tests/guix-graph.sh: Add test.
* doc/guix.texi (Invoking guix graph): Document it.

doc/guix.texi

@@ -9907,7 +9907,18 @@ The package dependency graph is largely architecture-independent, but there
 are some architecture-dependent bits that this option allows you to visualize.
 @end table
 
+On top of that, @command{guix graph} supports all the usual package
+transformation options (@pxref{Package Transformation Options}).  This
+makes it easy to view the effect of a graph-rewriting transformation
+such as @option{--with-input}.  For example, the command below outputs
+the graph of @code{git} once @code{openssl} has been replaced by
+@code{libressl} everywhere in the graph:
 
+@example
+guix graph git --with-input=openssl=libressl
+@end example
+
+So many possibilities, so much fun!
 
 @node Invoking guix publish
 @section Invoking @command{guix publish}

guix/scripts/graph.scm

@@ -32,6 +32,10 @@
   #:use-module (gnu packages)
   #:use-module (guix sets)
   #:use-module ((guix utils) #:select (location-file))
+  #:use-module ((guix scripts build)
+                #:select (show-transformation-options-help
+                          options->transformation
+                          %transformation-options))
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
@@ -446,7 +450,7 @@ package modules, while attempting to retain user package modules."
 ;;;
 
 (define %options
-  (list (option '(#\t "type") #t #f
+  (cons* (option '(#\t "type") #t #f
                  (lambda (opt name arg result)
                    (alist-cons 'node-type (lookup-node-type arg)
                                result)))
@@ -475,7 +479,9 @@ package modules, while attempting to retain user package modules."
                    (exit 0)))
          (option '(#\V "version") #f #f
                  (lambda args
-                  (show-version-and-exit "guix edit")))))
+                   (show-version-and-exit "guix graph")))
+
+         %transformation-options))
 
 (define (show-help)
   ;; TRANSLATORS: Here 'dot' is the name of a program; it must not be
@@ -495,6 +501,8 @@ Emit a representation of the dependency graph of PACKAGE...\n"))
   (display (G_ "
   -s, --system=SYSTEM    consider the graph for SYSTEM--e.g., \"i686-linux\""))
   (newline)
+  (show-transformation-options-help)
+  (newline)
   (display (G_ "
   -h, --help             display this help and exit"))
   (display (G_ "
@@ -514,21 +522,28 @@ Emit a representation of the dependency graph of PACKAGE...\n"))
 
 (define (guix-graph . args)
   (with-error-handling
-    (let* ((opts     (parse-command-line args %options
+    (define opts
+      (parse-command-line args %options
                           (list %default-options)
                           #:build-options? #f))
-           (backend  (assoc-ref opts 'backend))
+    (define backend
-           (type     (assoc-ref opts 'node-type))
+      (assoc-ref opts 'backend))
+    (define type
+      (assoc-ref opts 'node-type))
+
+    (with-store store
+      (let* ((transform (options->transformation opts))
              (items     (filter-map (match-lambda
                                       (('argument . (? store-path? item))
                                        item)
                                       (('argument . spec)
-                                    (specification->package spec))
+                                       (transform store
+                                                  (specification->package spec)))
                                       (('expression . exp)
-                                    (read/eval-package-expression exp))
+                                       (transform store
+                                                  (read/eval-package-expression exp)))
                                       (_ #f))
                                     opts)))
-      (with-store store
         ;; Ask for absolute file names so that .drv file names passed from the
         ;; user to 'read-derivation' are absolute when it returns.
         (with-fluids ((%file-port-name-canonicalization 'absolute))

tests/guix-graph.sh

@@ -1,5 +1,5 @@
 # GNU Guix --- Functional package management for GNU
-# Copyright © 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2015, 2016, 2019 Ludovic Courtès <ludo@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -53,3 +53,9 @@ cmp "$tmpfile1" "$tmpfile2"
 guix graph -t derivation coreutils > "$tmpfile1"
 guix graph -t derivation `guix build -d coreutils` > "$tmpfile2"
 cmp "$tmpfile1" "$tmpfile2"
+
+# Try package transformation options.
+guix graph git | grep 'label = "openssl'
+guix graph git --with-input=openssl=libressl | grep 'label = "libressl'
+if guix graph git --with-input=openssl=libressl | grep 'label = "openssl'
+then false; else true; fi