FIX: Avoid raising error when updating post and topic count user stats. (#15873)

There are still spots in the code base which results in us trying to turn the post and topic count negative. However,
we have a job that runs on a daily basis which will correct the count. Therefore, avoid raising an error for now
and log the exception instead.

app/services/user_stat_count_updater.rb

@@ -22,6 +22,18 @@ class UserStatCountUpdater
       elsif post.post_type == Post.types[:regular]
         stat.public_send(action, :post_count)
       end
+    rescue ActiveRecord::StatementInvalid => e
+      if e.cause.is_a?(PG::CheckViolation)
+        # There are still spots in the code base which results in the counter cache going out of sync. However,
+        # we have a job that runs on a daily basis which will correct the count. Therefore, avoid raising an error for now
+        # and log the exception instead.
+        Discourse.warn_exception(
+          e,
+          message: "Attempted to insert negative count into UserStat#post_count or UserStat#topic_count"
+        )
+      else
+        raise
+      end
     end
   end
 end

spec/services/user_stat_count_updater_spec.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe UserStatCountUpdater do
+  fab!(:user) { Fabricate(:user) }
+  fab!(:user_stat) { user.user_stat }
+  fab!(:post) { Fabricate(:post) }
+
+  before do
+    @orig_logger = Rails.logger
+    Rails.logger = @fake_logger = FakeLogger.new
+  end
+
+  after do
+    Rails.logger = @orig_logger
+  end
+
+  it 'should log the exception when a negative count is inserted' do
+    UserStatCountUpdater.decrement!(post, user_stat: user_stat)
+
+    expect(@fake_logger.warnings.first).to include("PG::CheckViolation")
+  end
+end