Remove :oj_json feature flag

Removes the :oj_json feature flag and defaults to the
OJ gem for most JSON requirements.

config/feature_flags/development/oj_json.yml

----
-name: oj_json
-introduced_by_url: 
-rollout_issue_url: 
-group: 
-type: development
-default_enabled: true

lib/gitlab/json.rb

@@ -67,15 +67,6 @@ module Gitlab
         ::JSON.pretty_generate(object, opts)
       end
 
-      # Feature detection for using Oj instead of the `json` gem.
-      #
-      # @return [Boolean]
-      def enable_oj?
-        return false unless feature_table_exists?
-
-        Feature.enabled?(:oj_json, default_enabled: true)
-      end
-
       private
 
       # Convert JSON string into Ruby through toggleable adapters.
@@ -91,11 +82,7 @@ module Gitlab
       def adapter_load(string, *args, **opts)
         opts = standardize_opts(opts)
 
-        if enable_oj?
         Oj.load(string, opts)
-        else
-          ::JSON.parse(string, opts)
-        end
       rescue Oj::ParseError, Encoding::UndefinedConversionError => ex
         raise parser_error.new(ex)
       end
@@ -120,11 +107,7 @@ module Gitlab
       #
       # @return [String]
       def adapter_dump(object, *args, **opts)
-        if enable_oj?
         Oj.dump(object, opts)
-        else
-          ::JSON.dump(object, *args)
-        end
       end
 
       # Generates JSON for an object but with fewer options, using toggleable adapters.
@@ -135,11 +118,7 @@ module Gitlab
       def adapter_generate(object, opts = {})
         opts = standardize_opts(opts)
 
-        if enable_oj?
         Oj.generate(object, opts)
-        else
-          ::JSON.generate(object, opts)
-        end
       end
 
       # Take a JSON standard options hash and standardize it to work across adapters
@@ -149,11 +128,8 @@ module Gitlab
       # @return [Hash]
       def standardize_opts(opts)
         opts ||= {}
-
-        if enable_oj?
         opts[:mode] = :rails
         opts[:symbol_keys] = opts[:symbolize_keys] || opts[:symbolize_names]
-        end
 
         opts
       end
@@ -213,7 +189,7 @@ module Gitlab
       # @param object [Object]
       # @return [String]
       def self.call(object, env = nil)
-        if Gitlab::Json.enable_oj? && Feature.enabled?(:grape_gitlab_json, default_enabled: true)
+        if Feature.enabled?(:grape_gitlab_json, default_enabled: true)
           Gitlab::Json.dump(object)
         else
           Grape::Formatter::Json.call(object, env)

spec/lib/gitlab/json_spec.rb

@@ -7,7 +7,6 @@ RSpec.describe Gitlab::Json do
     stub_feature_flags(json_wrapper_legacy_mode: true)
   end
 
-  shared_examples "json" do
   describe ".parse" do
     context "legacy_mode is disabled by default" do
       it "parses an object" do
@@ -295,12 +294,6 @@ RSpec.describe Gitlab::Json do
 
       subject.send(:handle_legacy_mode!, {})
     end
-
-      it "skips oj feature detection" do
-        expect(Feature).not_to receive(:enabled?).with(:oj_json, default_enabled: true)
-
-        subject.send(:enable_oj?)
-      end
   end
 
   context "the database is missing" do
@@ -316,35 +309,6 @@ RSpec.describe Gitlab::Json do
       expect(subject.dump({})).to eq("{}")
     end
   end
-  end
-
-  context "oj gem" do
-    before do
-      stub_feature_flags(oj_json: true)
-    end
-
-    it_behaves_like "json"
-
-    describe "#enable_oj?" do
-      it "returns true" do
-        expect(subject.enable_oj?).to be(true)
-      end
-    end
-  end
-
-  context "json gem" do
-    before do
-      stub_feature_flags(oj_json: false)
-    end
-
-    it_behaves_like "json"
-
-    describe "#enable_oj?" do
-      it "returns false" do
-        expect(subject.enable_oj?).to be(false)
-      end
-    end
-  end
 
   describe Gitlab::Json::GrapeFormatter do
     subject { described_class.call(obj, env) }
@@ -353,11 +317,6 @@ RSpec.describe Gitlab::Json do
     let(:env) { {} }
     let(:result) { "{\"test\":true}" }
 
-    context "oj is enabled" do
-      before do
-        stub_feature_flags(oj_json: true)
-      end
-
     context "grape_gitlab_json flag is enabled" do
       before do
         stub_feature_flags(grape_gitlab_json: true)
@@ -391,23 +350,6 @@ RSpec.describe Gitlab::Json do
     end
   end
 
-    context "oj is disabled" do
-      before do
-        stub_feature_flags(oj_json: false)
-      end
-
-      it "generates JSON" do
-        expect(subject).to eq(result)
-      end
-
-      it "uses Grape::Formatter::Json" do
-        expect(Grape::Formatter::Json).to receive(:call).with(obj, env)
-
-        subject
-      end
-    end
-  end
-
   describe Gitlab::Json::LimitedEncoder do
     subject { described_class.encode(obj, limit: 8.kilobytes) }