Add expires_in option for ActiveSupport::Cache::RedisStore#increment method (#7515)

* rails patch to fix expires_in for increment method

* fixup! rails patch to fix expires_in for increment method

correct test case

* fix redundant file name & class name

* add comment to explain monkey patch for RedisCacheStore#increment

config/initializers/active_support/cache/redis_cache_store.rb

@@ -0,0 +1,25 @@
+module ActiveSupport
+  module Cache
+    class RedisCacheStore
+      def increment(name, amount = 1, options = nil)
+        # With Rails 5.2.4, RedisCacheStore#increment method does not support option :expires_in.
+        # In order to workaround, we call expire command if the key is incremented at the first time.
+        # This patch should be removed when upgrading to Rails 6.
+        instrument :increment, name, amount: amount do
+          failsafe :increment do
+            options = merged_options(options)
+            key = normalize_key(name, options)
+            res = redis.with do |client|
+              client.incrby(key, amount).tap do
+                if options[:expires_in] && client.ttl(key).negative?
+                  client.expire(key, options[:expires_in].to_i)
+                end
+              end
+            end
+            res
+          end
+        end
+      end
+    end
+  end
+end

spec/initializers/active_support/cache/redis_cache_store_spec.rb

@@ -0,0 +1,48 @@
+require "rails_helper"
+
+RSpec.describe ActiveSupport::Cache::RedisCacheStore do
+  let(:redis_client) { ActiveSupport::Cache.lookup_store(:redis_cache_store).redis }
+  let(:cache_db) { described_class.new }
+  let(:key) { "monkey_patch_test" }
+
+  def value
+    cache_db.read(key, raw: true).to_i
+  end
+
+  def pttl
+    redis_client.pttl(key)
+  end
+
+  describe ".increment" do
+    before do
+      cache_db.delete(key)
+    end
+
+    it "increments value without expires_in" do
+      cache_db.increment(key)
+
+      expect(value).to eq(1)
+      expect(pttl).to eq(-1)
+
+      cache_db.increment(key)
+
+      expect(value).to eq(2)
+      expect(pttl).to eq(-1)
+    end
+
+    it "increments value with expires_in" do
+      cache_db.increment(key, 1, expires_in: 100.seconds)
+      first_pttl = pttl
+
+      expect(value).to eq(1)
+      expect(first_pttl > 0).to be_truthy
+      expect(first_pttl <= 100_000).to be_truthy
+
+      cache_db.increment(key, 1, expires_in: 200.seconds)
+      second_pttl = pttl
+
+      expect(value).to eq(2)
+      expect(second_pttl <= first_pttl).to be_truthy
+    end
+  end
+end