Raise errors while computing cache digests

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Raise errors encountered while computing a component's cache digest instead of degrading to an untracked component that can serve stale fragments.
+
+    *Erik Axel Nielsen*
+
 * Give `<% cache %>` blocks inside a component's own template a digest, for components that `include ViewComponent::ExperimentallyCacheable`.
 
     Rails digests the virtual path of whichever template is rendering. Inside a component that path resolves to no template, because component templates aren't in the view paths, so the Digestor returned an empty digest and the fragment was never invalidated. The only signal was a `Couldn't find template for digesting` line in the log. 4.15.0 fixed the case where the `cache` block wraps the component in a view. This fixes the case where the block sits in the component's template.

docs/guide/caching.md

@@ -204,6 +204,10 @@ The same works in a template, where the branch is often the more natural place f
 
 Declared components must include `ViewComponent::ExperimentallyCacheable` themselves, since a component that hasn't opted in has no digest to depend on.
 
+## When a digest can't be computed
+
+Computing a digest touches the autoloader, the filesystem, and Action View's dependency trackers, any of which can fail. ViewComponent lets those errors raise, matching Rails' digest behavior. Otherwise a component could become untracked and serve stale fragments without warning.
+
 ## Caveats
 
 **Self-caching components can't take content from their callers.** Besides a block, this covers `with_content` and slots set by the caller:

lib/view_component/cache_digest.rb

@@ -146,9 +146,6 @@ def partial_paths_in(source, name)
         RENDER_PARSER.new(name, source).render_calls.uniq.select do |path|
           source.include?(path) || source.include?(path.sub(%r{(\A|/)_}, '\1'))
         end
-      rescue
-        # Never let digest computation break rendering.
-        []
       end
 
       # Action View has shipped its render parser as a class (Rails 7.1, and
@@ -234,9 +231,6 @@ def constantize_component(constant_name)
         return unless component.respond_to?(:__vc_cacheable?) && component.__vc_cacheable?
 
         component
-      rescue
-        # Never let digest computation break rendering.
-        nil
       end
     end
 

lib/view_component/cache_digest/dependency_tracking.rb

@@ -27,11 +27,6 @@ def find_dependencies(name, template, view_paths = nil)
         end
 
         dependencies + CacheDigest.dependencies_in(template)
-      rescue
-        # A broken digest is preferable to a broken render. Falling back to the
-        # dependencies Rails found on its own means the component simply isn't
-        # tracked, which is the pre-existing behavior.
-        super
       end
 
       # @private

lib/view_component/cache_digest/resolver.rb

@@ -30,11 +30,6 @@ def find_templates(name, prefix, partial, details, locals = [])
         return [] unless component
 
         [build_template(component, virtual_path, details)]
-      rescue
-        # Never let digest resolution break rendering. Returning no template
-        # makes the Digestor treat this as a missing node, which degrades to
-        # the behavior components have without this feature.
-        []
       end
 
       def to_s

test/sandbox/app/components/cacheable_raising_ruby_dependency_component.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class CacheableRaisingRubyDependencyComponent < ViewComponent::Base
+  include ViewComponent::ExperimentallyCacheable
+
+  def call
+    render CacheDigestFixtures::RaisingRubyDependency.new
+  end
+end

test/sandbox/app/components/cacheable_raising_template_dependency_component.html.erb

@@ -0,0 +1 @@
+<%= render CacheDigestFixtures::RaisingTemplateDependency.new %>

test/sandbox/app/components/cacheable_raising_template_dependency_component.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class CacheableRaisingTemplateDependencyComponent < ViewComponent::Base
+  include ViewComponent::ExperimentallyCacheable
+end

test/sandbox/app/components/cacheable_unreadable_digest_source_component.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class CacheableUnreadableDigestSourceComponent < ViewComponent::Base
+  include ViewComponent::ExperimentallyCacheable
+
+  def call
+    "unreadable digest source"
+  end
+end

test/sandbox/app/components/cacheable_unreadable_digest_source_component.yml/placeholder

@@ -0,0 +1 @@
+This directory is intentionally unreadable as a digest source.

test/sandbox/config/application.rb

@@ -44,6 +44,7 @@ class Application < Rails::Application
 
     # Prepare test_set_no_duplicate_autoload_paths
     config.autoload_paths.push("#{config.root}/my/components/previews")
+    config.autoload_paths.push("#{config.root}/test/fixtures")
     config.view_component.previews.paths << "#{config.root}/my/components/previews"
     config.view_component.previews.paths << "#{Rails.root}/lib/component_previews"
 

test/sandbox/test/experimentally_cacheable_test.rb

@@ -41,6 +41,24 @@ def test_cache_digest_is_computable_outside_a_request
     refute_empty digest
   end
 
+  def test_cache_digest_raises_when_a_ruby_dependency_fails_to_load
+    error = assert_raises(RuntimeError) { CacheableRaisingRubyDependencyComponent.cache_digest }
+
+    assert_equal "raising Ruby dependency", error.message
+  end
+
+  def test_cache_digest_raises_when_a_template_dependency_fails_to_load
+    error = assert_raises(RuntimeError) { CacheableRaisingTemplateDependencyComponent.cache_digest }
+
+    assert_equal "raising template dependency", error.message
+  end
+
+  def test_cache_digest_raises_when_a_digest_source_cannot_be_read
+    error = assert_raises(Errno::EISDIR) { CacheableUnreadableDigestSourceComponent.cache_digest }
+
+    assert_includes error.message, "cacheable_unreadable_digest_source_component.yml"
+  end
+
   def test_cache_digest_changes_when_the_template_changes
     assert_digest_changes(
       "app/components/cacheable_component.html.erb",
@@ -203,12 +221,6 @@ def test_partial_paths_are_not_extracted_from_sources_without_render
     assert_empty ViewComponent::CacheDigest.partial_paths_in("def call; end", "a/b")
   end
 
-  def test_partial_path_extraction_swallows_parser_errors
-    ViewComponent::CacheDigest::RENDER_PARSER.stub(:new, ->(*) { raise "boom" }) do
-      assert_empty ViewComponent::CacheDigest.partial_paths_in("render \"a/b\"", "a/b")
-    end
-  end
-
   # Action View has shipped the parser as a class (7.1, main) and as a module
   # with a `Default` implementation (7.2 through 8.1). Exercised with doubles so
   # both shapes are covered whichever version is running.
@@ -479,37 +491,6 @@ def test_resolver_is_identified_by_class
     assert_equal resolver, ViewComponent::CacheDigest::Resolver.new
   end
 
-  def test_resolver_returns_no_template_when_synthesis_fails
-    resolver = ViewComponent::CacheDigest::Resolver.instance
-
-    ViewComponent::CacheDigest.stub(:component_for, ->(_) { raise "boom" }) do
-      assert_empty resolver.find_templates("cacheable_component", "view_component/cache_digest", true, {})
-    end
-  end
-
-  def test_dependency_tracking_falls_back_when_scanning_fails
-    template = build_template("<%= render CacheableComponent.new(title: 'a') %>")
-
-    ViewComponent::CacheDigest.stub(:dependencies_in, ->(_) { raise "boom" }) do
-      refute_includes(
-        ActionView::DependencyTracker.find_dependencies("some/template", template, []),
-        "view_component/cache_digest/cacheable_component"
-      )
-    end
-  end
-
-  def test_constantizing_swallows_unexpected_errors
-    Object.const_set(:BoomComponent, Class.new do
-      def self.__vc_cacheable?
-        raise ArgumentError
-      end
-    end)
-
-    assert_nil ViewComponent::CacheDigest.send(:constantize_component, "BoomComponent")
-  ensure
-    Object.send(:remove_const, :BoomComponent)
-  end
-
   def test_install_is_idempotent
     resolver_count = ActionController::Base.view_paths.count { |path| path.is_a?(ViewComponent::CacheDigest::Resolver) }
 

test/sandbox/test/fixtures/cache_digest_fixtures/raising_ruby_dependency.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+raise "raising Ruby dependency"

test/sandbox/test/fixtures/cache_digest_fixtures/raising_template_dependency.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+raise "raising template dependency"