Add first class component cache

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Add experimental support for caching by including `ViewComponent::ExperimentallyCacheable`.
+
+    *Reegan Viljoen*
+
 * Add `protocol` parameter to `with_request_url` test helper to enable testing with HTTPS protocol.
 
     *Joel Hawksley*
@@ -546,7 +550,7 @@ 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
 
@@ -1906,7 +1910,7 @@ 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)
 
@@ -2658,7 +2662,7 @@ 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*
 
@@ -2676,7 +2680,7 @@ 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.
 
@@ -3124,7 +3128,7 @@ _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 +1,45 @@
+---
+layout: default
+title: Caching
+parent: How-to guide
+---
+
+# Caching
+
+Experimental
+{: .label }
+
+Caching is experimental.
+
+To enable caching, include `ViewComponent::ExperimentallyCacheable`.
+
+Components implement caching by marking dependencies using `cache_on`:
+
+```ruby
+class CacheComponent < ViewComponent::Base
+  include ViewComponent::ExperimentallyCacheable
+
+  cache_on :foo, :bar
+  attr_reader :foo, :bar
+
+  def initialize(foo:, bar:)
+    @foo = foo
+    @bar = bar
+  end
+end
+```
+
+```erb
+<p><%= view_cache_dependencies.inspect %></p>
+
+<p><%= Time.zone.now %></p>
+<p><%= "#{foo} #{bar}" %></p>
+```
+
+`cache_on` accepts method names. Returned values are expanded via `ActiveSupport::Cache.expand_cache_key`, so Active Record models, `GlobalID`, arrays, and plain strings work as expected.
+
+Methods listed in `cache_on` may be private.
+
+The cache key includes a digest of component source (Ruby + templates + i18n sidecars) and rendered child ViewComponents.
+
+Partial/layout string dependencies are not currently included in the digest; modify `RAILS_CACHE_ID`/`RAILS_APP_VERSION` to invalidate on deploy.

lib/view_component.rb

@@ -12,6 +12,7 @@ module ViewComponent
   autoload :CompileCache
   autoload :Config
   autoload :Deprecation
+  autoload :ExperimentallyCacheable
   autoload :InlineTemplate
   autoload :Instrumentation
   autoload :Preview

lib/view_component/base.rb

@@ -50,7 +50,6 @@ def config
     include Rails.application.routes.url_helpers if defined?(Rails.application.routes)
     include ERB::Escape
     include ActiveSupport::CoreExt::ERBUtil
-
     include ViewComponent::InlineTemplate
     include ViewComponent::Slotable
     include ViewComponent::Translatable
@@ -68,7 +67,7 @@ def config
     # For Content Security Policy nonces
     delegate :content_security_policy_nonce, to: :helpers
 
-    # Config option that strips trailing whitespace in templates before compiling them.
+    # Config:attr_writer :attr_names option that strips trailing whitespace in templates before compiling them.
     class_attribute :__vc_strip_trailing_whitespace, instance_accessor: false, instance_predicate: false, default: false
 
     attr_accessor :__vc_original_view_context

lib/view_component/cache_digestor.rb

@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+require "digest"
+require "view_component/template_dependency_extractor"
+
+module ViewComponent
+  class CacheDigestor
+    def initialize(component:)
+      @component = component
+      @digests = {}
+      @file_cache = {}
+      @constant_cache = {}
+    end
+
+    def digest
+      digest_for_component(@component.class)
+    end
+
+    private
+
+    IN_PROGRESS = :__vc_in_progress
+    private_constant :IN_PROGRESS
+
+    def digest_for_component(component_class)
+      return "" unless component_class <= ViewComponent::Base
+      name = component_class.name
+      return "" unless name
+
+      cached_digest = @digests[name]
+      return "" if cached_digest == IN_PROGRESS
+      return cached_digest if cached_digest
+
+      @digests[name] = IN_PROGRESS
+
+      digest = Digest::SHA1.new
+
+      update_digest(digest, file_contents(component_class.identifier))
+
+      inline_template = component_class.__vc_inline_template
+      if inline_template
+        inline_source = inline_template.source
+        update_digest(digest, inline_source)
+        update_template_dependency_digests(digest, inline_source, inline_template.language)
+      end
+
+      template_paths = component_class.sidecar_files(ActionView::Template.template_handler_extensions).sort
+      template_paths.each do |path|
+        template_source = file_contents(path)
+        update_digest(digest, template_source)
+        update_template_dependency_digests(digest, template_source, File.extname(path).delete_prefix("."))
+      end
+
+      i18n_paths = component_class.sidecar_files(%w[yml yaml]).sort
+      i18n_paths.each do |path|
+        update_digest(digest, file_contents(path))
+      end
+
+      @digests[name] = digest.hexdigest
+    end
+
+    def update_template_dependency_digests(digest, template_source, handler)
+      return unless template_source&.include?("render")
+
+      dependencies = ViewComponent::TemplateDependencyExtractor.new(template_source, handler).extract
+      update_dependency_digests(digest, dependencies)
+    end
+
+    def update_dependency_digests(digest, dependencies)
+      dependencies.each do |dep|
+        next unless uppercase_constant?(dep)
+
+        klass = constantize(dep)
+        next unless klass
+
+        update_digest(digest, digest_for_component(klass))
+      end
+    end
+
+    def update_digest(digest, value)
+      return unless value
+
+      digest.update(value)
+      digest.update("\n")
+    end
+
+    def uppercase_constant?(dep)
+      return false unless dep
+
+      first = dep.getbyte(0)
+      first && first >= 65 && first <= 90
+    end
+
+    def constantize(constant_name)
+      @constant_cache.fetch(constant_name) do
+        @constant_cache[constant_name] = constant_name.safe_constantize
+      end
+    end
+
+    def file_contents(path)
+      return nil if path.nil?
+
+      @file_cache.fetch(path) do
+        @file_cache[path] = File.file?(path) ? File.read(path) : nil
+      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[:view_component_caching] = true
+
+      yield
+    ensure
+      ActiveSupport::IsolatedExecutionState[:view_component_caching] = caching_was
+    end
+  end
+end

lib/view_component/compiler.rb

@@ -90,13 +90,21 @@ 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 is_a?(ViewComponent::ExperimentallyCacheable)
+            __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 is_a?(ViewComponent::ExperimentallyCacheable)
+              __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