Normalize import_export structure

This brings a significant refactor to how
we handle `import_export.yml`, merge it with EE
and how we handle that for reader and saver.

This is meant to simplify the code, and remove
a ton of conditions to handle different models
of the structure.

This is also meant to prepare the structure
to extend it much easier, like adding `preload:`
or additional object types when needed.

This does not change the behavior of import/export,
rather unifies and simplifies the current implementation.

7 files changed, 198 insertions, 351 deletions

diff --git a/lib/gitlab/import_export/attributes_finder.rb b/lib/gitlab/import_export/attributes_finder.rb
index 42cd94add79..13883ca7f3d 100644
--- a/lib/gitlab/import_export/attributes_finder.rb
+++ b/lib/gitlab/import_export/attributes_finder.rb
@@ -3,35 +3,19 @@
 module Gitlab
   module ImportExport
     class AttributesFinder
-      def initialize(included_attributes:, excluded_attributes:, methods:)
-        @included_attributes = included_attributes || {}
-        @excluded_attributes = excluded_attributes || {}
-        @methods = methods || {}
+      def initialize(config:)
+        @tree = config[:tree] || {}
+        @included_attributes = config[:included_attributes] || {}
+        @excluded_attributes = config[:excluded_attributes] || {}
+        @methods = config[:methods] || {}
       end
 
-      def find(model_object)
-        parsed_hash = find_attributes_only(model_object)
-        parsed_hash.empty? ? model_object : { model_object => parsed_hash }
+      def find_root(model_key)
+        find(model_key, @tree[model_key])
       end
 
-      def parse(model_object)
-        parsed_hash = find_attributes_only(model_object)
-        yield parsed_hash unless parsed_hash.empty?
-      end
-
-      def find_included(value)
-        key = key_from_hash(value)
-        @included_attributes[key].nil? ? {} : { only: @included_attributes[key] }
-      end
-
-      def find_excluded(value)
-        key = key_from_hash(value)
-        @excluded_attributes[key].nil? ? {} : { except: @excluded_attributes[key] }
-      end
-
-      def find_method(value)
-        key = key_from_hash(value)
-        @methods[key].nil? ? {} : { methods: @methods[key] }
+      def find_relations_tree(model_key)
+        @tree[model_key]
       end
 
       def find_excluded_keys(klass_name)
@@ -40,12 +24,24 @@ module Gitlab
 
       private
 
-      def find_attributes_only(value)
-        find_included(value).merge(find_excluded(value)).merge(find_method(value))
+      def find(model_key, model_tree)
+        {
+          only: @included_attributes[model_key],
+          except: @excluded_attributes[model_key],
+          methods: @methods[model_key],
+          include: resolve_model_tree(model_tree)
+        }.compact
+      end
+
+      def resolve_model_tree(model_tree)
+        return unless model_tree
+
+        model_tree
+          .map(&method(:resolve_model))
       end
 
-      def key_from_hash(value)
-        value.is_a?(Hash) ? value.first.first : value
+      def resolve_model(model_key, model_tree)
+        { model_key => find(model_key, model_tree) }
       end
     end
   end
diff --git a/lib/gitlab/import_export/config.rb b/lib/gitlab/import_export/config.rb
index f6cd4eb5e0c..6f4919ead4e 100644
--- a/lib/gitlab/import_export/config.rb
+++ b/lib/gitlab/import_export/config.rb
@@ -3,70 +3,49 @@
 module Gitlab
   module ImportExport
     class Config
+      def initialize
+        @hash = parse_yaml
+        @hash.deep_symbolize_keys!
+        @ee_hash = @hash.delete(:ee) || {}
+
+        @hash[:tree] = normalize_tree(@hash[:tree])
+        @ee_hash[:tree] = normalize_tree(@ee_hash[:tree] || {})
+      end
+
       # Returns a Hash of the YAML file, including EE specific data if EE is
       # used.
       def to_h
-        hash = parse_yaml
-        ee_hash = hash['ee']
-
-        if merge? && ee_hash
-          ee_hash.each do |key, value|
-            if key == 'project_tree'
-              merge_project_tree(value, hash[key])
-            else
-              merge_attributes_list(value, hash[key])
-            end
-          end
+        if merge_ee?
+          deep_merge(@hash, @ee_hash)
+        else
+          @hash
         end
-
-        # We don't want to expose this section after this point, as it is no
-        # longer needed.
-        hash.delete('ee')
-
-        hash
       end
 
-      # Merges a project relationships tree into the target tree.
-      #
-      # @param [Array<Hash|Symbol>] source_values
-      # @param [Array<Hash|Symbol>] target_values
-      def merge_project_tree(source_values, target_values)
-        source_values.each do |value|
-          if value.is_a?(Hash)
-            # Examples:
-            #
-            # { 'project_tree' => [{ 'labels' => [...] }] }
-            # { 'notes' => [:author, { 'events' => [:push_event_payload] }] }
-            value.each do |key, val|
-              target = target_values
-                .find { |h| h.is_a?(Hash) && h[key] }
+      private
 
-              if target
-                merge_project_tree(val, target[key])
-              else
-                target_values << { key => val.dup }
-              end
-            end
-          else
-            # Example: :priorities, :author, etc
-            target_values << value
-          end
+      def deep_merge(hash_a, hash_b)
+        hash_a.deep_merge(hash_b) do |_, this_val, other_val|
+          this_val.to_a + other_val.to_a
         end
       end
 
-      # Merges a Hash containing a flat list of attributes, such as the entries
-      # in a `excluded_attributes` section.
-      #
-      # @param [Hash] source_values
-      # @param [Hash] target_values
-      def merge_attributes_list(source_values, target_values)
-        source_values.each do |key, values|
-          target_values[key] ||= []
-          target_values[key].concat(values)
+      def normalize_tree(item)
+        case item
+        when Array
+          item.reduce({}) do |hash, subitem|
+            hash.merge!(normalize_tree(subitem))
+          end
+        when Hash
+          item.transform_values(&method(:normalize_tree))
+        when Symbol
+          { item => {} }
+        else
+          raise ArgumentError, "#{item} needs to be Array, Hash, Symbol or NilClass"
         end
       end
 
-      def merge?
+      def merge_ee?
         Gitlab.ee?
       end
 
diff --git a/lib/gitlab/import_export/import_export.yml b/lib/gitlab/import_export/import_export.yml
index 40acb24d191..06c94beead8 100644
--- a/lib/gitlab/import_export/import_export.yml
+++ b/lib/gitlab/import_export/import_export.yml
@@ -3,89 +3,92 @@
 # This list _must_ only contain relationships that are available to both CE and
 # EE. EE specific relationships must be defined in the `ee` section further
 # down below.
-project_tree:
-  - labels:
-    - :priorities
-  - milestones:
-    - events:
-      - :push_event_payload
-  - issues:
-    - events:
-      - :push_event_payload
-    - :timelogs
-    - notes:
-      - :author
-      - events:
-        - :push_event_payload
-    - label_links:
-      - label:
-        - :priorities
-    - milestone:
-      - events:
-        - :push_event_payload
-    - resource_label_events:
-      - label:
-        - :priorities
-    - :issue_assignees
-  - snippets:
-    - :award_emoji
-    - notes:
-      - :author
-  - releases:
-    - :links
-  - project_members:
-    - :user
-  - merge_requests:
-    - :metrics
-    - notes:
-      - :author
+tree:
+  project:
+    - labels:
+      - :priorities
+    - milestones:
       - events:
         - :push_event_payload
-      - :suggestions
-    - merge_request_diff:
-      - :merge_request_diff_commits
-      - :merge_request_diff_files
-    - events:
-      - :push_event_payload
-    - :timelogs
-    - label_links:
-      - label:
-        - :priorities
-    - milestone:
+    - issues:
       - events:
         - :push_event_payload
-    - resource_label_events:
-      - label:
-        - :priorities
-  - ci_pipelines:
-    - notes:
-      - :author
+      - :timelogs
+      - notes:
+        - :author
+        - events:
+          - :push_event_payload
+      - label_links:
+        - label:
+          - :priorities
+      - milestone:
+        - events:
+          - :push_event_payload
+      - resource_label_events:
+        - label:
+          - :priorities
+      - :issue_assignees
+    - snippets:
+      - :award_emoji
+      - notes:
+        - :author
+    - releases:
+      - :links
+    - project_members:
+      - :user
+    - merge_requests:
+      - :metrics
+      - notes:
+        - :author
+        - events:
+          - :push_event_payload
+        - :suggestions
+      - merge_request_diff:
+        - :merge_request_diff_commits
+        - :merge_request_diff_files
       - events:
         - :push_event_payload
-    - stages:
-      - :statuses
-    - :external_pull_request
-  - :external_pull_requests
-  - :auto_devops
-  - :triggers
-  - :pipeline_schedules
-  - :services
-  - protected_branches:
-    - :merge_access_levels
-    - :push_access_levels
-  - protected_tags:
-    - :create_access_levels
-  - :project_feature
-  - :custom_attributes
-  - :prometheus_metrics
-  - :project_badges
-  - :ci_cd_settings
-  - :error_tracking_setting
-  - :metrics_setting
-  - boards:
-    - lists:
-      - label:
-        - :priorities
+      - :timelogs
+      - label_links:
+        - label:
+          - :priorities
+      - milestone:
+        - events:
+          - :push_event_payload
+      - resource_label_events:
+        - label:
+          - :priorities
+    - ci_pipelines:
+      - notes:
+        - :author
+        - events:
+          - :push_event_payload
+      - stages:
+        - :statuses
+      - :external_pull_request
+    - :external_pull_requests
+    - :auto_devops
+    - :triggers
+    - :pipeline_schedules
+    - :services
+    - protected_branches:
+      - :merge_access_levels
+      - :push_access_levels
+    - protected_tags:
+      - :create_access_levels
+    - :project_feature
+    - :custom_attributes
+    - :prometheus_metrics
+    - :project_badges
+    - :ci_cd_settings
+    - :error_tracking_setting
+    - :metrics_setting
+    - boards:
+      - lists:
+        - label:
+          - :priorities
+  group_members:
+    - :user
 
 # Only include the following attributes for the models specified.
 included_attributes:
@@ -225,12 +228,15 @@ methods:
     - :type
   lists:
     - :list_type
+  ci_pipelines:
+    - :notes
 
 # EE specific relationships and settings to include. All of this will be merged
 # into the previous structures if EE is used.
 ee:
-  project_tree:
-    - protected_branches:
-      - :unprotect_access_levels
-    - protected_environments:
-      - :deploy_access_levels
+  tree:
+    project:
+      protected_branches:
+        - :unprotect_access_levels
+      protected_environments:
+        - :deploy_access_levels
diff --git a/lib/gitlab/import_export/json_hash_builder.rb b/lib/gitlab/import_export/json_hash_builder.rb
deleted file mode 100644
index a92e3862361..00000000000
--- a/lib/gitlab/import_export/json_hash_builder.rb
+++ /dev/null
@@ -1,117 +0,0 @@
-# frozen_string_literal: true
-
-module Gitlab
-  module ImportExport
-    # Generates a hash that conforms with http://apidock.com/rails/Hash/to_json
-    # and its peculiar options.
-    class JsonHashBuilder
-      def self.build(model_objects, attributes_finder)
-        new(model_objects, attributes_finder).build
-      end
-
-      def initialize(model_objects, attributes_finder)
-        @model_objects = model_objects
-        @attributes_finder = attributes_finder
-      end
-
-      def build
-        process_model_objects(@model_objects)
-      end
-
-      private
-
-      # Called when the model is actually a hash containing other relations (more models)
-      # Returns the config in the right format for calling +to_json+
-      #
-      # +model_object_hash+ - A model relationship such as:
-      #   {:merge_requests=>[:merge_request_diff, :notes]}
-      def process_model_objects(model_object_hash)
-        json_config_hash = {}
-        current_key = model_object_hash.first.first
-
-        model_object_hash.values.flatten.each do |model_object|
-          @attributes_finder.parse(current_key) { |hash| json_config_hash[current_key] ||= hash }
-          handle_model_object(current_key, model_object, json_config_hash)
-        end
-
-        json_config_hash
-      end
-
-      # Creates or adds to an existing hash an individual model or list
-      #
-      # +current_key+ main model that will be a key in the hash
-      # +model_object+ model or list of models to include in the hash
-      # +json_config_hash+ the original hash containing the root model
-      def handle_model_object(current_key, model_object, json_config_hash)
-        model_or_sub_model = model_object.is_a?(Hash) ? process_model_objects(model_object) : model_object
-
-        if json_config_hash[current_key]
-          add_model_value(current_key, model_or_sub_model, json_config_hash)
-        else
-          create_model_value(current_key, model_or_sub_model, json_config_hash)
-        end
-      end
-
-      # Constructs a new hash that will hold the configuration for that particular object
-      # It may include exceptions or other attribute detail configuration, parsed by +@attributes_finder+
-      #
-      # +current_key+ main model that will be a key in the hash
-      # +value+ existing model to be included in the hash
-      # +json_config_hash+ the original hash containing the root model
-      def create_model_value(current_key, value, json_config_hash)
-        json_config_hash[current_key] = parse_hash(value) || { include: value }
-      end
-
-      # Calls attributes finder to parse the hash and add any attributes to it
-      #
-      # +value+ existing model to be included in the hash
-      # +parsed_hash+ the original hash
-      def parse_hash(value)
-        return if already_contains_methods?(value)
-
-        @attributes_finder.parse(value) do |hash|
-          { include: hash_or_merge(value, hash) }
-        end
-      end
-
-      def already_contains_methods?(value)
-        value.is_a?(Hash) && value.values.detect { |val| val[:methods]}
-      end
-
-      # Adds new model configuration to an existing hash with key +current_key+
-      # It may include exceptions or other attribute detail configuration, parsed by +@attributes_finder+
-      #
-      # +current_key+ main model that will be a key in the hash
-      # +value+ existing model to be included in the hash
-      # +json_config_hash+ the original hash containing the root model
-      def add_model_value(current_key, value, json_config_hash)
-        @attributes_finder.parse(value) do |hash|
-          value = { value => hash } unless value.is_a?(Hash)
-        end
-
-        add_to_array(current_key, json_config_hash, value)
-      end
-
-      # Adds new model configuration to an existing hash with key +current_key+
-      # it creates a new array if it was previously a single value
-      #
-      # +current_key+ main model that will be a key in the hash
-      # +value+ existing model to be included in the hash
-      # +json_config_hash+ the original hash containing the root model
-      def add_to_array(current_key, json_config_hash, value)
-        old_values = json_config_hash[current_key][:include]
-
-        json_config_hash[current_key][:include] = ([old_values] + [value]).compact.flatten
-      end
-
-      # Construct a new hash or merge with an existing one a model configuration
-      # This is to fulfil +to_json+ requirements.
-      #
-      # +hash+ hash containing configuration generated mainly from +@attributes_finder+
-      # +value+ existing model to be included in the hash
-      def hash_or_merge(value, hash)
-        value.is_a?(Hash) ? value.merge(hash) : { value => hash }
-      end
-    end
-  end
-end
diff --git a/lib/gitlab/import_export/project_tree_restorer.rb b/lib/gitlab/import_export/project_tree_restorer.rb
index 685cf53f27f..2dd18616cd6 100644
--- a/lib/gitlab/import_export/project_tree_restorer.rb
+++ b/lib/gitlab/import_export/project_tree_restorer.rb
@@ -58,11 +58,13 @@ module Gitlab
       # the configuration yaml file too.
       # Finally, it updates each attribute in the newly imported project.
       def create_relations
-        default_relation_list.each do |relation|
-          if relation.is_a?(Hash)
-            create_sub_relations(relation, @tree_hash)
-          elsif @tree_hash[relation.to_s].present?
-            save_relation_hash(@tree_hash[relation.to_s], relation)
+        project_relations_without_project_members.each do |relation_key, relation_definition|
+          relation_key_s = relation_key.to_s
+
+          if relation_definition.present?
+            create_sub_relations(relation_key_s, relation_definition, @tree_hash)
+          elsif @tree_hash[relation_key_s].present?
+            save_relation_hash(relation_key_s, @tree_hash[relation_key_s])
           end
         end
 
@@ -71,7 +73,7 @@ module Gitlab
         @saved
       end
 
-      def save_relation_hash(relation_hash_batch, relation_key)
+      def save_relation_hash(relation_key, relation_hash_batch)
         relation_hash = create_relation(relation_key, relation_hash_batch)
 
         remove_group_models(relation_hash) if relation_hash.is_a?(Array)
@@ -91,10 +93,13 @@ module Gitlab
         end
       end
 
-      def default_relation_list
-        reader.tree.reject do |model|
-          model.is_a?(Hash) && model[:project_members]
-        end
+      def project_relations_without_project_members
+        # We remove `project_members` as they are deserialized separately
+        project_relations.except(:project_members)
+      end
+
+      def project_relations
+        reader.attributes_finder.find_relations_tree(:project)
       end
 
       def restore_project
@@ -150,8 +155,7 @@ module Gitlab
       # issue, finds any subrelations such as notes, creates them and assign them back to the hash
       #
       # Recursively calls this method if the sub-relation is a hash containing more sub-relations
-      def create_sub_relations(relation, tree_hash, save: true)
-        relation_key = relation.keys.first.to_s
+      def create_sub_relations(relation_key, relation_definition, tree_hash, save: true)
         return if tree_hash[relation_key].blank?
 
         tree_array = [tree_hash[relation_key]].flatten
@@ -171,13 +175,13 @@ module Gitlab
           # But we can't have it in the upper level or GC won't get rid of the AR objects
           # after we save the batch.
           Project.transaction do
-            process_sub_relation(relation, relation_item)
+            process_sub_relation(relation_key, relation_definition, relation_item)
 
             # For every subrelation that hangs from Project, save the associated records altogether
             # This effectively batches all records per subrelation item, only keeping those in memory
             # We have to keep in mind that more batch granularity << Memory, but >> Slowness
             if save
-              save_relation_hash([relation_item], relation_key)
+              save_relation_hash(relation_key, [relation_item])
               tree_hash[relation_key].delete(relation_item)
             end
           end
@@ -186,37 +190,35 @@ module Gitlab
         tree_hash.delete(relation_key) if save
       end
 
-      def process_sub_relation(relation, relation_item)
-        relation.values.flatten.each do |sub_relation|
+      def process_sub_relation(relation_key, relation_definition, relation_item)
+        relation_definition.each do |sub_relation_key, sub_relation_definition|
           # We just use author to get the user ID, do not attempt to create an instance.
-          next if sub_relation == :author
+          next if sub_relation_key == :author
 
-          create_sub_relations(sub_relation, relation_item, save: false) if sub_relation.is_a?(Hash)
+          sub_relation_key_s = sub_relation_key.to_s
 
-          relation_hash, sub_relation = assign_relation_hash(relation_item, sub_relation)
-          relation_item[sub_relation.to_s] = create_relation(sub_relation, relation_hash) unless relation_hash.blank?
-        end
-      end
+          # create dependent relations if present
+          if sub_relation_definition.present?
+            create_sub_relations(sub_relation_key_s, sub_relation_definition, relation_item, save: false)
+          end
 
-      def assign_relation_hash(relation_item, sub_relation)
-        if sub_relation.is_a?(Hash)
-          relation_hash = relation_item[sub_relation.keys.first.to_s]
-          sub_relation = sub_relation.keys.first
-        else
-          relation_hash = relation_item[sub_relation.to_s]
+          # transform relation hash to actual object
+          sub_relation_hash = relation_item[sub_relation_key_s]
+          if sub_relation_hash.present?
+            relation_item[sub_relation_key_s] = create_relation(sub_relation_key, sub_relation_hash)
+          end
         end
-
-        [relation_hash, sub_relation]
       end
 
-      def create_relation(relation, relation_hash_list)
+      def create_relation(relation_key, relation_hash_list)
         relation_array = [relation_hash_list].flatten.map do |relation_hash|
-          Gitlab::ImportExport::RelationFactory.create(relation_sym: relation.to_sym,
-                                                       relation_hash: relation_hash,
-                                                       members_mapper: members_mapper,
-                                                       user: @user,
-                                                       project: @restored_project,
-                                                       excluded_keys: excluded_keys_for_relation(relation))
+          Gitlab::ImportExport::RelationFactory.create(
+            relation_sym: relation_key.to_sym,
+            relation_hash: relation_hash,
+            members_mapper: members_mapper,
+            user: @user,
+            project: @restored_project,
+            excluded_keys: excluded_keys_for_relation(relation_key))
         end.compact
 
         relation_hash_list.is_a?(Array) ? relation_array : relation_array.first
diff --git a/lib/gitlab/import_export/project_tree_saver.rb b/lib/gitlab/import_export/project_tree_saver.rb
index 2255635acdf..f1b3db6b208 100644
--- a/lib/gitlab/import_export/project_tree_saver.rb
+++ b/lib/gitlab/import_export/project_tree_saver.rb
@@ -18,7 +18,10 @@ module Gitlab
       def save
         mkdir_p(@shared.export_path)
 
-        File.write(full_path, project_json_tree)
+        project_tree = serialize_project_tree
+        fix_project_tree(project_tree)
+        File.write(full_path, project_tree.to_json)
+
         true
       rescue => e
         @shared.error(e)
@@ -27,27 +30,25 @@ module Gitlab
 
       private
 
-      def project_json_tree
+      def fix_project_tree(project_tree)
         if @params[:description].present?
-          project_json['description'] = @params[:description]
+          project_tree['description'] = @params[:description]
         end
 
-        project_json['project_members'] += group_members_json
-
-        RelationRenameService.add_new_associations(project_json)
+        project_tree['project_members'] += group_members_array
 
-        project_json.to_json
+        RelationRenameService.add_new_associations(project_tree)
       end
 
-      def project_json
-        @project_json ||= @project.as_json(reader.project_tree)
+      def serialize_project_tree
+        @project.as_json(reader.project_tree)
       end
 
       def reader
         @reader ||= Gitlab::ImportExport::Reader.new(shared: @shared)
       end
 
-      def group_members_json
+      def group_members_array
         group_members.as_json(reader.group_members_tree).each do |group_member|
           group_member['source_type'] = 'Project' # Make group members project members of the future import
         end
diff --git a/lib/gitlab/import_export/reader.rb b/lib/gitlab/import_export/reader.rb
index 8bdf6ca491d..9e81c6a3d07 100644
--- a/lib/gitlab/import_export/reader.rb
+++ b/lib/gitlab/import_export/reader.rb
@@ -7,42 +7,22 @@ module Gitlab
 
       def initialize(shared:)
         @shared = shared
-        config_hash = ImportExport::Config.new.to_h.deep_symbolize_keys
-        @tree = config_hash[:project_tree]
-        @attributes_finder = Gitlab::ImportExport::AttributesFinder.new(included_attributes: config_hash[:included_attributes],
-                                                                        excluded_attributes: config_hash[:excluded_attributes],
-                                                                        methods: config_hash[:methods])
+
+        @attributes_finder = Gitlab::ImportExport::AttributesFinder.new(
+          config: ImportExport::Config.new.to_h)
       end
 
       # Outputs a hash in the format described here: http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html
       # for outputting a project in JSON format, including its relations and sub relations.
       def project_tree
-        attributes = @attributes_finder.find(:project)
-        project_attributes = attributes.is_a?(Hash) ? attributes[:project] : {}
-
-        project_attributes.merge(include: build_hash(@tree))
+        attributes_finder.find_root(:project)
       rescue => e
         @shared.error(e)
         false
       end
 
       def group_members_tree
-        @attributes_finder.find_included(:project_members).merge(include: @attributes_finder.find(:user))
-      end
-
-      private
-
-      # Builds a hash in the format described here: http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html
-      #
-      # +model_list+ - List of models as a relation tree to be included in the generated JSON, from the _import_export.yml_ file
-      def build_hash(model_list)
-        model_list.map do |model_objects|
-          if model_objects.is_a?(Hash)
-            Gitlab::ImportExport::JsonHashBuilder.build(model_objects, @attributes_finder)
-          else
-            @attributes_finder.find(model_objects)
-          end
-        end
+        attributes_finder.find_root(:group_members)
       end
     end
   end