Merge branch 'fewer-constants-more-helpres' into 'master'

Fewer Git constants, more Git helpers.

See merge request !1727

app/services/git_push_service.rb

@@ -109,7 +109,7 @@ class GitPushService
 
   def push_to_existing_branch?(ref, oldrev)
     # Return if this is not a push to a branch (e.g. new commits)
-    Gitlab::Git.branch_ref?(ref) && oldrev != Gitlab::Git::BLANK_SHA
+    Gitlab::Git.branch_ref?(ref) && !Gitlab::Git.blank_ref?(oldrev)
   end
 
   def push_to_new_branch?(ref, oldrev)

app/workers/irker_worker.rb

@@ -57,9 +57,9 @@ class IrkerWorker
   end
 
   def send_branch_updates(push_data, project, repo_name, committer, branch)
-    if push_data['before'] == Gitlab::Git::BLANK_SHA
+    if Gitlab::Git.blank_ref?(push_data['before'])
       send_new_branch project, repo_name, committer, branch
-    elsif push_data['after'] == Gitlab::Git::BLANK_SHA
+    elsif Gitlab::Git.blank_ref?(push_data['after'])
       send_del_branch repo_name, committer, branch
     end
   end
@@ -83,7 +83,7 @@ class IrkerWorker
     return if push_data['total_commits_count'] == 0
 
     # Next message is for number of commit pushed, if any
-    if push_data['before'] == Gitlab::Git::BLANK_SHA
+    if Gitlab::Git.blank_ref?(push_data['before'])
       # Tweak on push_data["before"] in order to have a nice compare URL
       push_data['before'] = before_on_new_branch push_data, project
     end

lib/gitlab/force_push_check.rb

@@ -3,11 +3,12 @@ module Gitlab
     def self.force_push?(project, oldrev, newrev)
       return false if project.empty_repo?
 
-      if oldrev != Gitlab::Git::BLANK_SHA && newrev != Gitlab::Git::BLANK_SHA
+      # Created or deleted branch
+      if Gitlab::Git.blank_ref?(oldrev) || Gitlab::Git.blank_ref?(newrev)
+        false
+      else
         missed_refs, _ = Gitlab::Popen.popen(%W(git --git-dir=#{project.repository.path_to_repo} rev-list #{oldrev} ^#{newrev}))
         missed_refs.split("\n").size > 0
-      else
-        false
       end
     end
   end

lib/gitlab/push_data_builder.rb

@@ -71,7 +71,8 @@ module Gitlab
       end
 
       def checkout_sha(repository, newrev, ref)
-        if newrev != Gitlab::Git::BLANK_SHA && Gitlab::Git.tag_ref?(ref)
+        # Find sha for tag, except when it was deleted.
+        if Gitlab::Git.tag_ref?(ref) && !Gitlab::Git.blank_ref?(newrev)
           tag_name = Gitlab::Git.ref_name(ref)
           tag = repository.find_tag(tag_name)