Merge remote-tracking branch 'upstream/master' into no-ivar-in-modules

* upstream/master: (1723 commits)
  Resolve "Editor icons"
  Refactor issuable destroy action
  Ignore routes matching legacy_*_redirect in route specs
  Gitlab::Git::RevList and LfsChanges use lazy popen
  Gitlab::Git::Popen can lazily hand output to a block
  Merge branch 'master-i18n' into 'master'
  Remove unique validation from external_url in Environment
  Expose `duration` in Job API entity
  Add TimeCop freeze for DST and Regular time
  Harcode project visibility
  update a changelog
  Put a condition to old migration that adds fast_forward column to MRs
  Expose project visibility as CI variable
  fix flaky tests by removing unneeded clicks and focus actions
  fix flaky test in gfm_autocomplete_spec.rb
  Use Gitlab::Git operations for repository mirroring
  Encapsulate git operations for mirroring in Gitlab::Git
  Create a Wiki Repository's raw_repository properly
  Add `Gitlab::Git::Repository#fetch` command
  Fix Gitlab::Metrics::System#real_time and #monotonic_time doc
  ...

1 files changed, 61 insertions, 0 deletions

diff --git a/lib/gitlab/multi_collection_paginator.rb b/lib/gitlab/multi_collection_paginator.rb
new file mode 100644
index 00000000000..eb3c9002710
--- /dev/null
+++ b/lib/gitlab/multi_collection_paginator.rb
@@ -0,0 +1,61 @@
+module Gitlab
+  class MultiCollectionPaginator
+    attr_reader :first_collection, :second_collection, :per_page
+
+    def initialize(*collections, per_page: nil)
+      raise ArgumentError.new('Only 2 collections are supported') if collections.size != 2
+
+      @per_page = per_page || Kaminari.config.default_per_page
+      @first_collection, @second_collection = collections
+    end
+
+    def paginate(page)
+      page = page.to_i
+      paginated_first_collection(page) + paginated_second_collection(page)
+    end
+
+    def total_count
+      @total_count ||= first_collection.size + second_collection.size
+    end
+
+    private
+
+    def paginated_first_collection(page)
+      @first_collection_pages ||= Hash.new do |hash, page|
+        hash[page] = first_collection.page(page).per(per_page)
+      end
+
+      @first_collection_pages[page]
+    end
+
+    def paginated_second_collection(page)
+      @second_collection_pages ||= Hash.new do |hash, page|
+        second_collection_page = page - first_collection_page_count
+
+        offset = if second_collection_page < 1 || first_collection_page_count.zero?
+                   0
+                 else
+                   per_page - first_collection_last_page_size
+                 end
+        hash[page] = second_collection.page(second_collection_page)
+                       .per(per_page - paginated_first_collection(page).size)
+                       .padding(offset)
+      end
+
+      @second_collection_pages[page]
+    end
+
+    def first_collection_page_count
+      return @first_collection_page_count if defined?(@first_collection_page_count)
+
+      first_collection_page = paginated_first_collection(0)
+      @first_collection_page_count = first_collection_page.total_pages
+    end
+
+    def first_collection_last_page_size
+      return @first_collection_last_page_size if defined?(@first_collection_last_page_size)
+
+      @first_collection_last_page_size = paginated_first_collection(first_collection_page_count).count
+    end
+  end
+end