Add first class component cache

Gemfile.lock

@@ -4,6 +4,9 @@ PATH
     view_component (4.0.0.rc1)
       activesupport (>= 7.1.0, < 8.1)
       concurrent-ruby (~> 1)
+      haml (~> 6)
+      slim (~> 5)
+      temple (~> 0.10)
 
 GEM
   remote: https://rubygems.org/

docs/CHANGELOG.md

@@ -14,6 +14,10 @@ nav_order: 6
 
     *Joel Hawksley*, *Blake Williams*
 
+* Add experimental support for caching.
+
+    *Reegan Viljoen*
+
 ## 4.0.0.rc1
 
 Almost six years after releasing [v1.0.0](https://github.com/ViewComponent/view_component/releases/tag/v1.0.0), we're proud to ship the first release candidate of ViewComponent 4. This release marks a shift towards a Long Term Support model for the project, having reached significant feature maturity. While contributions are always welcome, we're unlikely to accept further breaking changes or major feature additions.
@@ -317,7 +321,7 @@ This release makes the following breaking changes:
 
 ## 3.23.0
 
-* Add docs about Slack channel in Ruby Central workspace. (Join us! #oss-view-component). Email [email protected] for an invite.
+* Add docs about Slack channel in Ruby Central workspace. (Join us! #oss-view-component). Email <[email protected]> for an invite.
 
     *Joel Hawksley
 
@@ -1773,7 +1777,7 @@ Run into an issue with this release? [Let us know](https://github.com/ViewCompon
 
     *Joel Hawksley*
 
-* The ViewComponent team at GitHub is hiring! We're looking for a Rails engineer with accessibility experience: [https://boards.greenhouse.io/github/jobs/4020166](https://boards.greenhouse.io/github/jobs/4020166). Reach out to [email protected] with any questions!
+* The ViewComponent team at GitHub is hiring! We're looking for a Rails engineer with accessibility experience: [https://boards.greenhouse.io/github/jobs/4020166](https://boards.greenhouse.io/github/jobs/4020166). Reach out to <[email protected]> with any questions!
 
 * The ViewComponent team is hosting a happy hour at RailsConf. Join us for snacks, drinks, and stickers: [https://www.eventbrite.com/e/viewcomponent-happy-hour-tickets-304168585427](https://www.eventbrite.com/e/viewcomponent-happy-hour-tickets-304168585427)
 
@@ -2537,7 +2541,7 @@ Run into an issue with this release? [Let us know](https://github.com/ViewCompon
 
     *Matheus Richard*
 
-* Are you interested in building the future of ViewComponent? GitHub is looking to hire a Senior Engineer to work on Primer ViewComponents and ViewComponent. Apply here: [US/Canada](https://github.com/careers) / [Europe](https://boards.greenhouse.io/github/jobs/3132294). Feel free to reach out to [email protected] with any questions.
+* Are you interested in building the future of ViewComponent? GitHub is looking to hire a Senior Engineer to work on Primer ViewComponents and ViewComponent. Apply here: [US/Canada](https://github.com/careers) / [Europe](https://boards.greenhouse.io/github/jobs/3132294). Feel free to reach out to <[email protected]> with any questions.
 
     *Joel Hawksley*
 
@@ -2555,7 +2559,7 @@ Run into an issue with this release? [Let us know](https://github.com/ViewCompon
 
 ## 2.31.0
 
-_Note: This release includes an underlying change to Slots that may affect incorrect usage of the API, where Slots were set on a line prefixed by `<%=`. The result of setting a Slot shouldn't be returned. (`<%`)_
+*Note: This release includes an underlying change to Slots that may affect incorrect usage of the API, where Slots were set on a line prefixed by `<%=`. The result of setting a Slot shouldn't be returned. (`<%`)*
 
 * Add `#with_content` to allow setting content without a block.
 
@@ -3003,7 +3007,7 @@ _Note: This release includes an underlying change to Slots that may affect incor
 
   * The gem name is now `view_component`.
   * ViewComponent previews are now accessed at `/rails/view_components`.
-  * ViewComponents can _only_ be rendered with the instance syntax: `render(MyComponent.new)`. Support for all other syntaxes has been removed.
+  * ViewComponents can *only* be rendered with the instance syntax: `render(MyComponent.new)`. Support for all other syntaxes has been removed.
   * ActiveModel::Validations have been removed. ViewComponent generators no longer include validations.
   * In Rails 6.1, no monkey patching is used.
   * `to_component_class` has been removed.

docs/guide/caching.md

@@ -0,0 +1,42 @@
+---
+layout: default
+title: Caching
+parent: How-to guide
+---
+
+# Caching
+
+Experimental
+{: .label }
+
+Components can implement caching by marking the depndencies that a digest can be built om using the cache_on macro, like so:
+
+```ruby
+class CacheComponent < ViewComponent::Base
+  include ViewComponent::Cacheable
+
+  cache_on :foo, :bar
+  attr_reader :foo, :bar
+
+  def initialize(foo:, bar:)
+    @foo = foo
+    @bar = bar
+  end
+end
+```
+
+```erb
+<p><%= view_cache_dependencies %></p>
+
+<p><%= Time.zone.now %>"></p>
+<p><%= "#{foo} #{bar}" %></p>
+```
+
+will result in:
+
+```html
+<p>foo-bar</p>
+
+<p>2025-03-27 16:46:10 UTC</p>
+<p> foo bar</p>
+```

lib/view_component/base.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "action_view"
+require "view_component/cacheable"
 require "active_support/configurable"
 require "view_component/collection"
 require "view_component/compile_cache"
@@ -50,11 +51,11 @@ def config
     include Rails.application.routes.url_helpers if defined?(Rails) && Rails.application
     include ERB::Escape
     include ActiveSupport::CoreExt::ERBUtil
-
     include ViewComponent::InlineTemplate
     include ViewComponent::Slotable
     include ViewComponent::Translatable
     include ViewComponent::WithContentHelper
+    include ViewComponent::Cacheable
 
     # For CSRF authenticity tokens in forms
     delegate :form_authenticity_token, :protect_against_forgery?, :config, to: :helpers
@@ -69,10 +70,12 @@ def config
     delegate :content_security_policy_nonce, to: :helpers
 
     # Config option that strips trailing whitespace in templates before compiling them.
-    class_attribute :__vc_strip_trailing_whitespace, instance_accessor: false, instance_predicate: false, default: false
 
     class_attribute :__vc_response_format, instance_accessor: false, instance_predicate: false, default: nil
 
+    class_attribute :__vc_strip_trailing_whitespace, instance_accessor: false, instance_predicate: false
+    self.__vc_strip_trailing_whitespace = false # class_attribute:default doesn't work until Rails 5.2
+
     attr_accessor :__vc_original_view_context
     attr_reader :current_template
 
@@ -312,12 +315,6 @@ def virtual_path
       self.class.virtual_path
     end
 
-    # For caching, such as #cache_if
-    # @private
-    def view_cache_dependencies
-      []
-    end
-
     # The current request. Use sparingly as doing so introduces coupling that
     # inhibits encapsulation & reuse, often making testing difficult.
     #

lib/view_component/cache_digestor.rb

@@ -0,0 +1,21 @@
+# # frozen_string_literal: true
+
+require "view_component/template_dependency_extractor"
+
+module ViewComponent
+  class CacheDigestor
+    def initialize(component:)
+      @component = component
+    end
+
+    def digest
+      template = @component.current_template
+      if template.nil? && template == :inline_call
+        []
+      else
+        template_string = template.source
+        ViewComponent::TemplateDependencyExtractor.new(template_string, template.details.handler).extract
+      end
+    end
+  end
+end

lib/view_component/cache_registry.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module ViewComponent
+  module CachingRegistry
+    extend self
+
+    def caching?
+      ActiveSupport::IsolatedExecutionState[:view_component_caching] ||= false
+    end
+
+    def track_caching
+      caching_was = ActiveSupport::IsolatedExecutionState[:view_component_caching]
+      ActiveSupport::IsolatedExecutionState[:action_view_caching] = true
+
+      yield
+    ensure
+      ActiveSupport::IsolatedExecutionState[:view_component_caching] = caching_was
+    end
+  end
+end

lib/view_component/cacheable.rb

@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require "view_component/cache_registry"
+require "view_component/cache_digestor"
+
+module ViewComponent::Cacheable
+  extend ActiveSupport::Concern
+
+  included do
+    class_attribute :__vc_cache_options, default: Set[:identifier]
+    class_attribute :__vc_cache_dependencies, default: Set.new
+
+    # For caching, such as #cache_if
+    #
+    # @private
+    def view_cache_dependencies
+      self.class.__vc_cache_dependencies.map { |dep| public_send(dep) }
+    end
+
+    def view_cache_options
+      return if __vc_cache_options.blank?
+
+      computed_view_cache_options = __vc_cache_options.map { |opt| if respond_to?(opt) then public_send(opt) end }
+      combined_fragment_cache_key(ActiveSupport::Cache.expand_cache_key(computed_view_cache_options + component_digest))
+    end
+
+    # Render component from cache if possible
+    #
+    # @private
+    def __vc_render_cacheable(safe_call)
+      if (__vc_cache_options - [:identifier]).any?
+        ViewComponent::CachingRegistry.track_caching do
+          template_fragment(safe_call)
+        end
+      else
+        instance_exec(&safe_call)
+      end
+    end
+
+    def template_fragment
+      if (content = read_fragment)
+        @view_renderer.cache_hits[@current_template&.virtual_path] = :hit if defined?(@view_renderer)
+        content
+      else
+        @view_renderer.cache_hits[@current_template&.virtual_path] = :miss if defined?(@view_renderer)
+        write_fragment
+      end
+    end
+
+    def read_fragment
+      Rails.cache.fetch(view_cache_options)
+    end
+
+    def write_fragment
+      content = instance_exec(&safe_call)
+      Rails.cache.fetch(view_cache_options) do
+        content
+      end
+      content
+    end
+
+    def combined_fragment_cache_key(key)
+      cache_key = [:view_component, ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"], key]
+      cache_key.flatten!(1)
+      cache_key.compact!
+      cache_key
+    end
+
+    def component_digest
+      ViewComponent::CacheDigestor.new(component: self).digest
+    end
+  end
+
+  class_methods do
+    # For caching the component
+    def cache_on(*args)
+      __vc_cache_options.merge(args)
+    end
+
+    def inherited(child)
+      child.__vc_cache_options = __vc_cache_options.dup
+
+      super
+    end
+  end
+end

lib/view_component/compiler.rb

@@ -97,13 +97,21 @@ def define_render_template_for
         safe_call = template.safe_method_name_call
         @component.define_method(:render_template_for) do |_|
           @current_template = template
-          instance_exec(&safe_call)
+          if @component.respond_to?(:__vc_render_cacheable)
+            @component.__vc_render_cacheable(safe_call)
+          else
+            instance_exec(&safe_call)
+          end
         end
       else
         compiler = self
         @component.define_method(:render_template_for) do |details|
           if (@current_template = compiler.find_templates_for(details).first)
-            instance_exec(&@current_template.safe_method_name_call)
+            if @component.respond_to?(:__vc_render_cacheable)
+              @component.__vc_render_cacheable(@current_template.safe_method_name_call)
+            else
+              instance_exec(&@current_template.safe_method_name_call)
+            end
           else
             raise MissingTemplateError.new(self.class.name, details)
           end

lib/view_component/prism_render_dependency_extractor.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require "prism"
+
+module ViewComponent
+  class PrismRenderDependencyExtractor
+    def initialize(code)
+      @code = code
+      @dependencies = []
+    end
+
+    def extract
+      result = Prism.parse(@code)
+      walk(result.value)
+      @dependencies
+    end
+
+    private
+
+    def walk(node)
+      return unless node.respond_to?(:child_nodes)
+
+      if node.is_a?(Prism::CallNode) && render_call?(node)
+        extract_render_target(node)
+      end
+
+      node.child_nodes.each { |child| walk(child) if child }
+    end
+
+    def render_call?(node)
+      node.receiver.nil? && node.name == :render
+    end
+
+    def extract_render_target(node)
+      args = node.arguments&.arguments
+      return unless args && !args.empty?
+
+      first_arg = args.first
+
+      if first_arg.is_a?(Prism::CallNode) &&
+          first_arg.name == :new &&
+          first_arg.receiver.is_a?(Prism::ConstantPathNode) || first_arg.receiver.is_a?(Prism::ConstantReadNode)
+
+        const = extract_constant_path(first_arg.receiver)
+        @dependencies << const if const
+      end
+    end
+
+    def extract_constant_path(const_node)
+      parts = []
+      current = const_node
+
+      while current
+        case current
+        when Prism::ConstantPathNode
+          parts.unshift(current.child.name)
+          current = current.parent
+        when Prism::ConstantReadNode
+          parts.unshift(current.name)
+          break
+        else
+          break
+        end
+      end
+
+      parts.join("::")
+    end
+  end
+end