1 files changed, 96 insertions, 0 deletions
diff --git a/actionview/lib/action_view/log_subscriber.rb b/actionview/lib/action_view/log_subscriber.rb
new file mode 100644
index 0000000000..227f025385
--- /dev/null
+++ b/actionview/lib/action_view/log_subscriber.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+require "active_support/log_subscriber"
+
+module ActionView
+  # = Action View Log Subscriber
+  #
+  # Provides functionality so that Rails can output logs from Action View.
+  class LogSubscriber < ActiveSupport::LogSubscriber
+    VIEWS_PATTERN = /^app\/views\//
+
+    def initialize
+      @root = nil
+      super
+    end
+
+    def render_template(event)
+      info do
+        message = +"  Rendered #{from_rails_root(event.payload[:identifier])}"
+        message << " within #{from_rails_root(event.payload[:layout])}" if event.payload[:layout]
+        message << " (Duration: #{event.duration.round(1)}ms | Allocations: #{event.allocations})"
+      end
+    end
+
+    def render_partial(event)
+      info do
+        message = +"  Rendered #{from_rails_root(event.payload[:identifier])}"
+        message << " within #{from_rails_root(event.payload[:layout])}" if event.payload[:layout]
+        message << " (Duration: #{event.duration.round(1)}ms | Allocations: #{event.allocations})"
+        message << " #{cache_message(event.payload)}" unless event.payload[:cache_hit].nil?
+        message
+      end
+    end
+
+    def render_collection(event)
+      identifier = event.payload[:identifier] || "templates"
+
+      info do
+        "  Rendered collection of #{from_rails_root(identifier)}" \
+        " #{render_count(event.payload)} (Duration: #{event.duration.round(1)}ms | Allocations: #{event.allocations})"
+      end
+    end
+
+    def start(name, id, payload)
+      if name == "render_template.action_view"
+        log_rendering_start(payload)
+      end
+
+      super
+    end
+
+    def logger
+      ActionView::Base.logger
+    end
+
+  private
+
+    EMPTY = ""
+    def from_rails_root(string) # :doc:
+      string = string.sub(rails_root, EMPTY)
+      string.sub!(VIEWS_PATTERN, EMPTY)
+      string
+    end
+
+    def rails_root # :doc:
+      @root ||= "#{Rails.root}/"
+    end
+
+    def render_count(payload) # :doc:
+      if payload[:cache_hits]
+        "[#{payload[:cache_hits]} / #{payload[:count]} cache hits]"
+      else
+        "[#{payload[:count]} times]"
+      end
+    end
+
+    def cache_message(payload) # :doc:
+      case payload[:cache_hit]
+      when :hit
+        "[cache hit]"
+      when :miss
+        "[cache miss]"
+      end
+    end
+
+    def log_rendering_start(payload)
+      info do
+        message = +"  Rendering #{from_rails_root(payload[:identifier])}"
+        message << " within #{from_rails_root(payload[:layout])}" if payload[:layout]
+        message
+      end
+    end
+  end
+end
+
+ActionView::LogSubscriber.attach_to :action_view