guix hash: Add --exclude-vcs option.

* guix/scripts/hash.scm (show-help): Add help text for --exclude-vcs option.
(%options): Add --exclude-vcs option.
(guix-hash): Handle exclude-vcs option.
* doc/guix.texi ("Invoking guix hash"): Update doc.
* tests/guix-hash.sh: Add test.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -4678,7 +4678,7 @@ The general syntax is:
 guix hash @var{option} @var{file}
 @end example
 
-@command{guix hash} has the following option:
+@command{guix hash} has the following options:
 
 @table @code
 
@@ -4706,6 +4706,11 @@ hash (@pxref{Invoking guix archive}).
 @c FIXME: Replace xref above with xref to an ``Archive'' section when
 @c it exists.
 
+@item --exclude-vcs
+@itemx -x
+When combined with @option{--recursive}, exclude version control system
+directories (@file{.bzr}, @file{.git}, @file{.hg}, etc.)
+
 @vindex git-fetch
 As an example, here is how you would compute the hash of a Git checkout,
 which is useful when using the @code{git-fetch} method (@pxref{origin
@@ -4714,8 +4719,7 @@ Reference}):
 @example
 $ git clone http://example.org/foo.git
 $ cd foo
-$ rm -rf .git
+$ guix hash -rx .
-$ guix hash -r .
 @end example
 @end table
 

guix/scripts/hash.scm

@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2016 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
+;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -48,6 +49,8 @@ Return the cryptographic hash of FILE.
 
 Supported formats: 'nix-base32' (default), 'base32', and 'base16' ('hex'
 and 'hexadecimal' can be used as well).\n"))
+  (format #t (_ "
+  -x, --exclude-vcs      exclude version control directories"))
   (format #t (_ "
   -f, --format=FMT       write the hash in the given format"))
   (format #t (_ "
@@ -62,7 +65,10 @@ and 'hexadecimal' can be used as well).\n"))
 
 (define %options
   ;; Specification of the command-line options.
-  (list (option '(#\f "format") #t #f
+  (list (option '(#\x "exclude-vcs") #f #f
+                (lambda (opt name arg result)
+                  (alist-cons 'exclude-vcs? #t result)))
+        (option '(#\f "format") #t #f
                 (lambda (opt name arg result)
                   (define fmt-proc
                     (match arg
@@ -81,7 +87,6 @@ and 'hexadecimal' can be used as well).\n"))
         (option '(#\r "recursive") #f #f
                 (lambda (opt name arg result)
                   (alist-cons 'recursive? #t result)))
-
         (option '(#\h "help") #f #f
                 (lambda args
                   (show-help)
@@ -107,13 +112,23 @@ and 'hexadecimal' can be used as well).\n"))
                   (alist-cons 'argument arg result))
                 %default-options))
 
+  (define (vcs-file? file stat)
+    (case (stat:type stat)
+      ((directory)
+       (member (basename file) '(".bzr" ".git" ".hg" ".svn" "CVS")))
+      (else
+       #f)))
+
   (let* ((opts (parse-options))
          (args (filter-map (match-lambda
                             (('argument . value)
                              value)
                             (_ #f))
                            (reverse opts)))
-         (fmt  (assq-ref opts 'format)))
+         (fmt  (assq-ref opts 'format))
+         (select? (if (assq-ref opts 'exclude-vcs?)
+                      (negate vcs-file?)
+                      (const #t))))
 
     (define (file-hash file)
       ;; Compute the hash of FILE.
@@ -121,7 +136,7 @@ and 'hexadecimal' can be used as well).\n"))
       (with-error-handling
         (if (assoc-ref opts 'recursive?)
             (let-values (((port get-hash) (open-sha256-port)))
-              (write-file file port)
+              (write-file file port #:select? select?)
               (flush-output-port port)
               (get-hash))
             (call-with-input-file file port-sha256))))

tests/guix-hash.sh

@@ -1,5 +1,6 @@
 # GNU Guix --- Functional package management for GNU
 # Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -46,3 +47,18 @@ then false; else true; fi
 # the archive format doesn't support.
 if guix hash -r /dev/null
 then false; else true; fi
+
+# Adding a .git directory
+mkdir "$tmpdir/.git"
+touch "$tmpdir/.git/foo"
+
+# ...changes the hash
+test `guix hash -r $tmpdir` = 0a50z04zyzf7pidwxv0nwbj82pgzbrhdy9562kncnvkcfvb48m59
+
+# ...but remains the same when using `-x'
+test `guix hash -r $tmpdir -x` = 10k1lw41wyrjf9mxydi0is5nkpynlsvgslinics4ppir13g7d74p
+
+# Without '-r', this should fail.
+if guix hash "$tmpdir"
+then false; else true; fi
+