1 files changed, 72 insertions, 0 deletions
diff --git a/lib/gitlab/database/migrations/squasher.rb b/lib/gitlab/database/migrations/squasher.rb
new file mode 100644
index 00000000000..98fdf873aa5
--- /dev/null
+++ b/lib/gitlab/database/migrations/squasher.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+require 'set'
+
+module Gitlab
+  module Database
+    module Migrations
+      class Squasher
+        RSPEC_FILENAME_REGEXP = /\A([0-9]+_)?([_a-z0-9]*)\.rb\z/
+
+        def initialize(git_output)
+          @migration_data = migration_files_from_git(git_output).filter_map do |mf|
+            basename = Pathname(mf).basename.to_s
+            file_name_match = ActiveRecord::Migration::MigrationFilenameRegexp.match(basename)
+            slug = file_name_match[2]
+            unless slug == 'init_schema'
+              {
+                path: mf,
+                basename: basename,
+                timestamp: file_name_match[1],
+                slug: slug
+              }
+            end
+          end
+        end
+
+        def files_to_delete
+          @migration_data.pluck(:path) + schema_migrations + find_migration_specs
+        end
+
+        private
+
+        def schema_migrations
+          @migration_data.map { |m| "db/schema_migrations/#{m[:timestamp]}" }
+        end
+
+        def find_migration_specs
+          @file_slugs = Set.new @migration_data.pluck(:slug)
+          (migration_specs + ee_migration_specs).select { |f| file_has_slug?(f) }
+        end
+
+        def migration_files_from_git(body)
+          body.chomp
+              .split("\n")
+              .select { |fn| fn.end_with?('.rb') }
+        end
+
+        def match_file_slug(filename)
+          m = RSPEC_FILENAME_REGEXP.match(filename)
+          return if m.nil?
+
+          m[2].sub(/_spec$/, '')
+        end
+
+        def file_has_slug?(filename)
+          spec_slug = match_file_slug(Pathname(filename).basename.to_s)
+          return false if spec_slug.nil?
+
+          @file_slugs.include?(spec_slug)
+        end
+
+        def migration_specs
+          Dir.glob(Rails.root.join('spec/migrations/*.rb'))
+        end
+
+        def ee_migration_specs
+          Dir.glob(Rails.root.join('ee/spec/migrations/*.rb'))
+        end
+      end
+    end
+  end
+end