Fix Gitlab::Git::Repository#commit returns wrong commit, if commit_id is "tag name".

lib/extracts_path.rb

@@ -98,9 +98,7 @@ module ExtractsPath
     @ref, @path = extract_ref(@id)
-    # It is used "@project.repository.commits(@ref, @path, 1, 0)",
-    # because "@project.repository.commit(@ref)" returns wrong commit when @ref is tag name.
-    @commit = @project.repository.commits(@ref, @path, 1, 0).first
+    @commit = @project.repository.commit(@ref)
     @tree = Tree.new(@project.repository, @commit.id, @ref, @path)

lib/gitlab/git/repository.rb

@@ -49,7 +49,16 @@ module Gitlab
       def commit(commit_id = nil)
         commit = if commit_id
-                   repo.commit(commit_id)
+                   # Find repo.refs first,
+                   # because if commit_id is "tag name",
+                   # repo.commit(commit_id) returns wrong commit sha
+                   # that is git tag object sha.
+                   ref = repo.refs.find {|r| r.name == commit_id}
+                   if ref
+                     ref.commit
+                   else
+                     repo.commit(commit_id)
+                   end
                  else
                    repo.commits(root_ref).first
                  end