Skip cache digest scans that can't find anything

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Speed up cold cache digests by skipping the `# Template Dependency:` scan for sources that declare none, and by not translating class names in synthetic templates, which only declare paths.
+
+    *Erik Axel Nielsen*
+
 ## 4.22.0
 
 * Comment on release pull requests with benchmark results compared to the previous release.

lib/view_component/cache_digest/dependency_tracking.rb

@@ -21,6 +21,10 @@ def find_dependencies(name, template, view_paths = nil)
           dependencies = super
           source = template.source
 
+          # Synthetic templates already declare every dependency found in their
+          # sources, as paths.
+          next dependencies if name.start_with?("#{CacheDigest::VIRTUAL_PATH_PREFIX}/")
+
           # `# Template Dependency: SomeComponent` names a class, which Rails
           # would resolve as a template path and never find. Swap it for the path
           # the component is digested under, so the declaration resolves instead
@@ -29,8 +33,6 @@ def find_dependencies(name, template, view_paths = nil)
             dependencies = dependencies - [declared] + [virtual_path]
           end
 
-          # Synthetic templates already declare every dependency found in their sources.
-          next dependencies if name.start_with?("#{CacheDigest::VIRTUAL_PATH_PREFIX}/")
           next dependencies unless CacheDigest.template_dependencies?(source, template.handler)
 
           component_paths, inferred_partials =

lib/view_component/cache_digest/resolver.rb

@@ -184,6 +184,10 @@ def template_sources(component)
 
       def explicit_dependencies(sources)
         sources.flat_map { |source|
+          # A cheap check first: most sources declare nothing, and the
+          # pattern is slow to scan for in sources with many comments.
+          next [] unless source.include?("Template Dependency:")
+
           declared = source.scan(CacheDigest::EXPLICIT_DEPENDENCY).flatten
 
           # Component class names are translated to the path they're digested