Merge pull request Shopify#1149 from Shopify/liquid-usage

Add usage tracking

README.md

@@ -106,3 +106,9 @@ template = Liquid::Template.parse("{{x}} {{y}}")
 template.render!({ 'x' => 1}, { strict_variables: true })
 #=> Liquid::UndefinedVariable: Liquid error: undefined variable y
 ```
+
+### Usage tracking
+
+To help track usages of a feature or code path in production, we have released opt-in usage tracking. To enable this, we provide an empty `Liquid:: Usage.increment` method which you can customize to your needs. The feature is well suited to https://github.com/Shopify/statsd-instrument. However, the choice of implementation is up to you.
+
+Once you have enabled usage tracking, we recommend reporting any events through Github Issues that your system may be logging. It is highly likely this event has been added to consider deprecating or improving code specific to this event, so please raise any concerns.

lib/liquid.rb

@@ -75,6 +75,7 @@ module Liquid
 require 'liquid/tokenizer'
 require 'liquid/parse_context'
 require 'liquid/partial_cache'
+require 'liquid/usage'
 
 # Load all the tags of the standard library
 #

lib/liquid/standardfilters.rb

@@ -421,6 +421,7 @@ def at_most(input, n)
 
     def default(input, default_value = ''.freeze)
       if !input || input.respond_to?(:empty?) && input.empty?
+        Usage.increment("default_filter_received_false_value") if input == false # See https://github.com/Shopify/liquid/issues/1127
         default_value
       else
         input

lib/liquid/usage.rb

@@ -0,0 +1,6 @@
+module Liquid
+  module Usage
+    def self.increment(name)
+    end
+  end
+end