a simple approach using shell commands

plugins/gh-pages.lisp

@@ -1,6 +1,38 @@
+(eval-when (:compile-toplevel :load-toplevel)
+  (ql:quickload 'puri :silent t))
 (defpackage :coleslaw-gh-pages
   (:use :cl)
+  (:import-from :coleslaw
+                #:*config*
+                #:domain
+                #:deploy
+                #:staging-dir
+                #:deploy-dir)
   (:export #:enable))
 
 (in-package :coleslaw-gh-pages)
 
+(defvar *options* nil)
+
+(defmethod deploy (staging)
+  (uiop:run-program (list* (namestring
+                            (merge-pathnames "plugins/publish-gh-pages.sh"
+                                             coleslaw-conf:*basedir*))
+                           (namestring
+                            (merge-pathnames (staging-dir *config*)))
+                           (namestring
+                            (merge-pathnames (deploy-dir *config*)))
+                           *options*)
+                    :output t
+                    :error-output t))
+
+(defun enable (&key url (branch "gh-pages") (remote "origin") cname)
+  (check-type url string)
+  (check-type remote string)
+  (check-type branch string)
+  (if (eq t cname)
+      (progn
+        (setf cname (puri:uri-host (puri:parse-uri (domain *config*))))
+        (check-type cname string)
+        (setf *options* (list url branch remote cname)))
+      (setf *options* (list url branch remote))))

plugins/publish-gh-pages.sh

@@ -0,0 +1,55 @@
+#!/bin/bash -x
+
+set -e
+
+staging=$1
+deploy=$2
+url=$3
+branch=$4
+remote=$5
+cname=$6
+
+if [[ -d $deploy && ! -d $deploy/.git ]]
+then
+   echo "Target directory $deploy exists and is not a git repository. Aborting" >&2
+   exit 1
+fi
+
+if [[ ! -d $deploy ]]
+then
+    git clone --no-checkout --origin $remote $url $deploy
+fi
+
+cd $deploy
+
+# safe and most reliable way to check if the branch exist
+if git show-ref --verify --quiet refs/heads/$branch
+then
+    # if the branch exists locally
+    git checkout $branch
+elif git show-ref --verify --quiet refs/remotes/$remote/$branch
+then
+    # if the branch does not exist locally but exist in the specified remote ---
+    # Note, git checkout $branch will search the branch with the same name with
+    # ALL remotes, and set it as the tracking branch if there is a single such
+    # remote, but does not allow the user to necessarily specify which.
+    git checkout -b $branch --track $remote/$branch
+else
+    # if there is no matching branch, make an orphan branch
+    git checkout --orphan $branch
+fi
+
+rsync -avz --delete --exclude .git/ --copy-links $staging $deploy
+
+if [[ ! -z "$cname" ]]
+then
+    echo $cname > CNAME
+fi
+
+git add -A                      # add all changes in the worktree
+git add $(git ls-files -o )     # add all untracked files in the worktree
+
+git commit -m "Deployed on $(date)"
+
+git push $remote $branch
+