[bug#50072] [PATCH WIP 1/4] guix hash: Extract file hashing procedures.

[Sarah Morgensen <iskarian@mgsn.dev>]

* guix/scripts/hash.scm (guix-hash)[vcs-file?, file-hash]: Extract logic
to...
* guix/hash.scm: ...here. New file.
---
 guix/hash.scm         | 51 +++++++++++++++++++++++++++++++++++++++++++
 guix/scripts/hash.scm | 29 ++++++------------------
 2 files changed, 58 insertions(+), 22 deletions(-)
 create mode 100644 guix/hash.scm

diff --git a/guix/hash.scm b/guix/hash.scm
new file mode 100644
index 0000000000..8c2ab8187f
--- /dev/null
+++ b/guix/hash.scm
@@ -0,0 +1,51 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix hash)
+  #:use-module (gcrypt hash)
+  #:use-module (guix serialization)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:export (vcs-file?
+            file-hash*))
+
+(define (vcs-file? file stat)
+  "Returns true if FILE is a version control system file."
+  (case (stat:type stat)
+    ((directory)
+     (member (basename file) '(".bzr" ".git" ".hg" ".svn" "CVS")))
+    ((regular)
+     ;; Git sub-modules have a '.git' file that is a regular text file.
+     (string=? (basename file) ".git"))
+    (else
+     #f)))
+
+(define* (file-hash* file #:key
+                     (algorithm (hash-algorithm sha256))
+                     (recursive? #t)
+                     (select? (negate vcs-file?)))
+  "Compute the hash of FILE with ALGORITHM.  If RECURSIVE? is true, recurse
+into subdirectories of FILE, computing the combined hash of all files for
+which (SELECT?  FILE STAT) returns true."
+  (if recursive?
+      (let-values (((port get-hash)
+                    (open-hash-port algorithm)))
+        (write-file file port #:select? select?)
+        (force-output port)
+        (get-hash))
+      (file-hash algorithm file)))
diff --git a/guix/scripts/hash.scm b/guix/scripts/hash.scm
index b8622373cc..353ca30c2c 100644
--- a/guix/scripts/hash.scm
+++ b/guix/scripts/hash.scm
@@ -3,6 +3,7 @@
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2018 Tim Gesthuizen <tim.gesthuizen@yahoo.de>
+;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -23,6 +24,7 @@
   #:use-module (gcrypt hash)
   #:use-module (guix serialization)
   #:use-module (guix ui)
+  #:use-module (guix hash)
   #:use-module (guix scripts)
   #:use-module (guix base16)
   #:use-module (guix base32)
@@ -125,16 +127,6 @@ and 'base16' ('hex' and 'hexadecimal' can be used as well).\n"))
     (parse-command-line args %options (list %default-options)
                         #:build-options? #f))
 
-  (define (vcs-file? file stat)
-    (case (stat:type stat)
-      ((directory)
-       (member (basename file) '(".bzr" ".git" ".hg" ".svn" "CVS")))
-      ((regular)
-       ;; Git sub-modules have a '.git' file that is a regular text file.
-       (string=? (basename file) ".git"))
-      (else
-       #f)))
-
   (let* ((opts (parse-options))
          (args (filter-map (match-lambda
                             (('argument . value)
@@ -150,18 +142,11 @@ and 'base16' ('hex' and 'hexadecimal' can be used as well).\n"))
       ;; Compute the hash of FILE.
       ;; Catch and gracefully report possible '&nar-error' conditions.
       (with-error-handling
-        (if (assoc-ref opts 'recursive?)
-            (let-values (((port get-hash)
-                          (open-hash-port (assoc-ref opts 'hash-algorithm))))
-              (write-file file port #:select? select?)
-              (force-output port)
-              (get-hash))
-            (match file
-              ("-" (port-hash (assoc-ref opts 'hash-algorithm)
-                              (current-input-port)))
-              (_   (call-with-input-file file
-                     (cute port-hash (assoc-ref opts 'hash-algorithm)
-                           <>)))))))
+        (match file
+          ("-" (port-hash (assoc-ref opts 'hash-algorithm)
+                          (current-input-port)))
+          (_   (file-hash* #:algorithm (assoc-ref opts 'hash-algorithm)
+                           #:recursive? (assoc-ref opts 'recursive?))))))
 
     (match args
       ((file)
-- 
2.31.1