guix: Add git utility module.

* guix/git.scm: New file.
* Makefile.am (MODULES): Add new file.

2 files changed, 165 insertions, 0 deletions

diff --git a/Makefile.am b/Makefile.am
index 22ba00e900..64a7a92657 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -126,6 +126,7 @@ MODULES =					\
   guix/build/make-bootstrap.scm			\
   guix/search-paths.scm				\
   guix/packages.scm				\
+  guix/git.scm					\
   guix/potluck/build-systems.scm		\
   guix/potluck/licenses.scm			\
   guix/potluck/packages.scm			\
diff --git a/guix/git.scm b/guix/git.scm
new file mode 100644
index 0000000000..02f61edacb
--- /dev/null
+++ b/guix/git.scm
@@ -0,0 +1,164 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2017 Andy Wingo <wingo@pobox.com>
+;;;
+;;; 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 git)
+  #:use-module (guix utils)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
+  #:use-module (ice-9 format)
+  #:use-module (ice-9 popen)
+  #:use-module (ice-9 rdelim)
+  #:export (&git-condition
+            git-condition?
+            git-condition-argv
+            git-condition-output
+            git-condition-status
+
+            false-if-git-error
+
+            git-check-ref-format
+            git-rev-parse
+            git-config
+            git-describe
+            git-fetch
+            git-push
+            git-clone
+            git-reset
+            git-add
+            git-commit))
+
+;;; Commentary:
+;;;
+;;; A simple collection of Scheme wrappers for Git functionality.
+;;;
+;;; Code:
+
+(define-condition-type &git-condition &condition git-condition?
+  (argv git-condition-argv)
+  (output git-condition-output)
+  (status git-condition-status))
+
+(define-syntax-rule (false-if-git-error body0 body ...)
+  (guard (c ((git-condition? c) #f))
+    body0 body ...))
+
+(define (shell:quote str)
+  (with-output-to-string
+    (lambda ()
+      (display #\')
+      (string-for-each (lambda (ch)
+                         (if (eqv? ch #\')
+                             (begin (display #\\) (display #\'))
+                             (display ch)))
+                       str)
+      (display #\'))))
+
+(define (run env input-file args)
+  (define (prepend-env args)
+    (if (null? env)
+        args
+        (cons "env" (append env args))))
+  (define (redirect-input args)
+    (if input-file
+        (list "sh" "-c"
+              (string-append (string-join (map shell:quote args) " ")
+                             "<" input-file))
+        args))
+  (let* ((real-args (redirect-input (prepend-env args)))
+         (pipe (apply open-pipe* OPEN_READ real-args))
+         (output (read-string pipe))
+         (ret (close-pipe pipe)))
+    (case (status:exit-val ret)
+      ((0) output)
+      (else (raise (condition (&git-condition
+                               (argv real-args)
+                               (output output)
+                               (status ret))))))))
+
+(define* (git* args #:key (input #f) (env '()))
+  (if input
+      (call-with-temporary-output-file
+       (lambda (file-name file-port)
+         (display input file-port)
+         (close-port file-port)
+         (run env file-name (cons* "git" args))))
+      (run env #f (cons* "git" args))))
+
+(define (git . args)
+  (git* args))
+
+(define* (git-check-ref-format str #:key allow-onelevel?)
+  "Raise an exception if @var{str} is not a valid Git ref."
+  (when (string-prefix? "-" str)
+    (error "bad ref" str))
+  (git "check-ref-format"
+       (if allow-onelevel? "--allow-onelevel" "--no-allow-onelevel")
+       str))
+
+(define (git-rev-parse rev)
+  "Parse the string @var{rev} and return a Git commit hash, as a string."
+  (string-trim-both (git "rev-parse" rev)))
+
+(define (git-config key)
+  "Return the configuration value for @var{key}, as a string."
+  (string-trim-both (git "config" key)))
+
+(define* (git-describe #:optional (ref "HEAD"))
+  "Run @command{git describe} on the given @var{ref}, defaulting to
+@code{HEAD}, and return the resulting string."
+  (string-trim-both (git "describe")))
+
+(define (git-fetch)
+  "Run @command{git fetch} in the current working directory."
+  (git "fetch"))
+
+(define (git-push)
+  "Run @command{git push} in the current working directory."
+  (git "push"))
+
+(define (git-clone repo dir)
+  "Check out @var{repo} into @var{dir}."
+  (git "clone" "--" repo dir))
+
+(define* (git-reset #:key (ref "HEAD") (mode 'hard))
+  ;; Can't let the ref be mistaken for a command-line argument.
+  "Reset the current working directory to @var{ref}.  Available values for
+@var{mode} are the symbols @code{hard}, @code{soft}, and @code{mixed}."
+  (when (string-prefix? "-" ref)
+    (error "bad ref" ref))
+  (git "reset"
+       (case mode
+         ((hard) "--hard")
+         ((mixed) "--mixed")
+         ((soft) "--soft")
+         (else (error "unknown mode" mode)))
+       ref))
+
+(define (git-add file)
+  "Add @var{file} to the index in the current working directory."
+  (git "add" "--" file))
+
+(define* (git-commit #:key message author-name author-email)
+  "Commit the changes in the current working directory, with the message
+@var{message}.  The commit will be attributed to the author with the name and
+email address @var{author-name} and @var{author-email}, respectively."
+  (git* (list "commit" (string-append "--message=" message))
+        #:env (list (string-append "GIT_COMMITTER_NAME=" author-name)
+                    (string-append "GIT_COMMITTER_EMAIL=" author-email)
+                    (string-append "GIT_AUTHOR_NAME=" author-name)
+                    (string-append "GIT_AUTHOR_EMAIL=" author-email))))