Replace `omf.util_sync` with `omf.repo.pull`

Based on
https://github.com/Homebrew/homebrew/blob/master/Library/Homebrew/cmd/update.rb#L175-L221

pkg/omf/cli/omf.install.fish

@@ -41,7 +41,7 @@ function omf.install -a type_flag name_or_url
   if test -e $OMF_PATH/$target
     echo (omf::dim)"Updating $name_or_url $install_type..."(omf::off)
     pushd $OMF_PATH/$target
-    omf.util_sync "origin" >/dev/null ^&1
+    omf.repo.pull
     popd
     echo (omf::em)"✔ $name_or_url $install_type up to date."(omf::off)
   else

pkg/omf/cli/omf.repo.pull.fish

+function omf.repo.pull
+  set initial_branch (command git symbolic-ref -q --short HEAD); or return $OMF_UNKNOWN_ERR
+  set initial_revision (command git rev-parse -q --verify HEAD); or return $OMF_UNKNOWN_ERR
+
+  if not command git diff --quiet
+    echo (omf::em)"Stashing your changes:"(omf::off)
+    command git status --short --untracked-files
+
+    command git stash save --include-untracked --quiet
+    set stashed true
+  end
+
+  if test "$initial_branch" != master
+    command git checkout master --quiet
+  end
+
+  # the refspec ensures that 'origin/master' gets updated
+  command git pull --rebase --quiet origin "refs/heads/master:refs/remotes/origin/master"
+  if test $status -eq 2 #SIGINT
+    command git checkout $initial_branch
+    command git reset --hard $initial_revision
+    test "$stashed" = true; and command git stash pop
+  end
+
+  if test "$initial_branch" != master
+    command git checkout $initial_branch --quiet
+  end
+
+  if test "$stashed" = true
+    command git stash pop --quiet
+
+    echo (omf::em)"Restored your changes:"(omf::off)
+    command git status --short --untracked-files
+  end
+end

pkg/omf/cli/omf.update.fish

@@ -10,7 +10,7 @@ function omf.update
     if git pull --rebase $repo master >/dev/null ^&1
       git stash apply >/dev/null ^&1
     else
-      omf.util_sync "origin"
+      omf.repo.sync
     end
   end
 end

pkg/omf/util/omf.util_sync.fish

-function omf.util_sync -a remote
-  set -l repo $remote
-  set -q argv[1]; and set repo $argv[1]
-
-  git fetch origin master
-  git reset --hard FETCH_HEAD
-  git clean -df
-end