Invert feature gating: required_features → missing_features

.github/workflows/ruby.yml

@@ -20,3 +20,5 @@ jobs:
       run: bundle exec rake test
     - name: Run liquid-spec
       run: bundle exec rake run
+    - name: Check feature tag coverage
+      run: bundle exec rake coverage_check

README.md

@@ -90,10 +90,9 @@ LiquidSpec.setup do
   require "my_liquid"
 end
 
-# Declare which features you support
+# Declare what your adapter can't handle (default: run everything)
 LiquidSpec.configure do |config|
-  config.features = [:core]  # enables liquid_ruby suite
-  # Add :shopify_tags, :shopify_objects, :shopify_filters for Shopify themes
+  config.missing_features = [:shopify_tags, :shopify_filters]
 end
 
 # Parse template source into a template object
@@ -146,15 +145,15 @@ Each spec includes a detailed `hint` explaining how the feature should be implem
 
 ### Feature-Based Suite Selection
 
-Suites run based on feature declarations:
+Suites run by default. Declare what your adapter can't handle to skip specific specs:
 
 ```ruby
 LiquidSpec.configure do |config|
-  # Just core Liquid (liquid_ruby + shopify_production_recordings)
-  config.features = [:core]
-  
-  # Full Shopify theme support (adds shopify_theme_dawn)
-  config.features = [:core, :shopify_tags, :shopify_objects, :shopify_filters]
+  # Run everything (default — empty denylist)
+  config.missing_features = []
+
+  # Skip Shopify-specific specs (for adapters without Shopify extensions)
+  config.missing_features = [:shopify_tags, :shopify_objects, :shopify_filters]
 end
 ```
 

Rakefile

@@ -49,6 +49,60 @@ task :matrix do
   system("bundle", "exec", "ruby", "bin/liquid-spec", "matrix", "--all") || abort
 end
 
+desc "Verify every spec feature tag is covered by at least one reference adapter"
+task :coverage_check do
+  require "yaml"
+  require "set"
+
+  base = File.expand_path(__dir__)
+
+  # Collect all feature tags used across spec YAML files
+  spec_tags = Set.new
+  Dir.glob(File.join(base, "specs/**/*.yml")).each do |f|
+    begin
+      data = YAML.safe_load(File.read(f), permitted_classes: [Symbol, Range], aliases: true)
+      next unless data
+
+      meta = data.is_a?(Hash) ? (data["_metadata"] || {}) : {}
+      (meta["features"] || []).each { |t| spec_tags << t.to_sym }
+
+      specs = data.is_a?(Hash) ? (data["specs"] || []) : (data.is_a?(Array) ? data : [])
+      specs.each do |spec|
+        (spec["features"] || []).each { |t| spec_tags << t.to_sym } if spec.is_a?(Hash)
+      end
+    rescue
+    end
+  end
+
+  # Extract missing_features from each reference adapter via static analysis.
+  # We parse the config.missing_features = [...] line rather than loading the
+  # adapter (which would require all adapter dependencies to be installed).
+  adapter_files = Dir.glob(File.join(base, "examples/*.rb"))
+  adapter_missing = {}
+  adapter_files.each do |path|
+    source = File.read(path)
+    if (m = source.match(/config\.missing_features\s*=\s*\[(.*?)\]/m))
+      symbols = m[1].scan(/:(\w+)/).flatten.map(&:to_sym)
+      adapter_missing[File.basename(path)] = symbols.to_set
+    end
+  end
+
+  if adapter_missing.empty?
+    abort "Coverage check FAILED — no reference adapters found in examples/"
+  end
+
+  # Check: every tag must be NOT-missing in at least one adapter
+  orphans = spec_tags.reject do |tag|
+    adapter_missing.any? { |_, missing| !missing.include?(tag) }
+  end
+
+  if orphans.any?
+    abort "Coverage check FAILED — no reference adapter covers these tags:\n  #{orphans.sort.join(', ')}\n\nAdd an example adapter that does not include these in missing_features."
+  else
+    puts "Coverage check passed: all #{spec_tags.size} feature tags covered across #{adapter_missing.size} reference adapters."
+  end
+end
+
 # Spec generation tasks (only needed for development)
 import("tasks/liquid_ruby.rake")
 import("tasks/standard_filters.rake")

examples/json_rpc_ruby_liquid.rb

@@ -45,7 +45,7 @@
 LiquidSpec.configure do |config|
   # JSON-RPC adapters support core features including runtime_drops
   # because they implement bidirectional callbacks
-  config.features = [:core, :strict_parsing]
+  config.missing_features = [:ruby_types, :ruby_drops, :binary_data, :lax_parsing, :activesupport, :template_factory, :shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_c.rb

@@ -36,7 +36,7 @@ def parse_expression(markup, safe: false)
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :lax_parsing]
+  config.missing_features = [:runtime_drops, :ruby_types, :ruby_drops, :binary_data, :activesupport, :template_factory, :shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_c_strict.rb

@@ -24,7 +24,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :strict_parsing]
+  config.missing_features = [:runtime_drops, :ruby_types, :ruby_drops, :binary_data, :lax_parsing, :activesupport, :template_factory, :shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby.rb

@@ -19,7 +19,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :strict_parsing, :strict2_parsing, :ruby_types]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access, :activesupport, :lax_parsing]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby_activesupport.rb

@@ -24,7 +24,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :activesupport, :strict_parsing]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access, :lax_parsing]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby_lax.rb

@@ -19,7 +19,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :lax_parsing]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access, :activesupport]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby_lax_activesupport.rb

@@ -24,7 +24,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :lax_parsing, :activesupport]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby_shopify.rb

@@ -183,7 +183,7 @@ def render_to_output_buffer(context, output)
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :strict_parsing, :ruby_types, :shopify_filters]
+  config.missing_features = [:lax_parsing]
   config.suites = [:benchmarks]
   config.filter = "shopify_"
 end

examples/liquid_ruby_yjit.rb

@@ -21,7 +21,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :strict_parsing, :strict2_parsing, :ruby_types]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access, :activesupport, :lax_parsing]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

examples/liquid_ruby_zjit.rb

@@ -21,7 +21,7 @@
 end
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :strict_parsing, :strict2_parsing, :ruby_types]
+  config.missing_features = [:shopify_filters, :shopify_includes, :shopify_blank, :shopify_error_handling, :shopify_error_format, :shopify_string_access, :activesupport, :lax_parsing]
 end
 
 LiquidSpec.compile do |ctx, source, parse_options|

lib/liquid/spec/adapter_runner.rb

@@ -10,11 +10,11 @@ class AdapterRunner
       TEST_TIME = Time.utc(2024, 1, 1, 0, 1, 58).freeze
       TEST_TZ = "America/New_York"
 
-      attr_reader :name, :features, :ctx
+      attr_reader :name, :missing_features, :ctx
 
       def initialize(name: nil)
         @name = name
-        @features = Set.new([:core])
+        @missing_features = Set.new
         @setup_block = nil
         @compile_block = nil
         @render_block = nil
@@ -43,8 +43,8 @@ def load_dsl(path)
         @render_block = ::LiquidSpec.instance_variable_get(:@render_block)
 
         config = ::LiquidSpec.instance_variable_get(:@config)
-        if config&.respond_to?(:features)
-          set_features(config.features)
+        if config&.respond_to?(:missing_features)
+          set_missing_features(config.missing_features)
         end
 
         # Validate block signatures
@@ -145,15 +145,14 @@ def on_render(&block)
         @render_block = block
       end
 
-      # Set features
-      def set_features(features)
-        @features = Set.new(features.map(&:to_sym))
-        @features << :core unless @features.include?(:core)
+      # Set missing features
+      def set_missing_features(missing_features)
+        @missing_features = Set.new(missing_features.map(&:to_sym))
       end
 
       # Check if adapter can run a spec
       def can_run?(spec)
-        spec.runnable_with?(@features)
+        !spec.skipped_by?(@missing_features)
       end
 
       # Run a batch of specs
@@ -189,7 +188,7 @@ def run_single(spec)
           return SpecResult.new(
             spec: spec,
             status: :skipped,
-            reason: "Missing features: #{(spec.required_features - @features.to_a).join(", ")}",
+            reason: "Adapter does not support: #{(spec.features & @missing_features.to_a).join(", ")}",
           )
         end
 

lib/liquid/spec/cli/adapter_dsl.rb

@@ -13,7 +13,7 @@
 #
 #   LiquidSpec.configure do |config|
 #     config.suite = :liquid_ruby
-#     config.features = [:core, :lax_parsing]
+#     config.missing_features = [:shopify_tags]
 #   end
 #
 #   LiquidSpec.compile do |ctx, source, parse_options|
@@ -67,57 +67,35 @@ def format_timeout(value)
     shopify_error_handling: "Shopify-specific error handling and recovery behavior",
   }.freeze
 
-  # Feature expansions - declaring a feature automatically includes these
-  # :core is the "full implementation" feature that includes runtime drop support
-  # JSON-RPC adapters that can't support runtime drops should not declare :core
-  FEATURE_EXPANSIONS = {
-    core: [:runtime_drops, :inline_errors],
-  }.freeze
-
-  # Default features when no config is set (matches Configuration defaults after expansion)
-  DEFAULT_FEATURES = [:core, :runtime_drops, :inline_errors].freeze
-
   class Configuration
     attr_accessor :suite, :filter, :verbose, :strict_only
-    attr_reader :features, :known_failures, :suites
+    attr_reader :missing_features, :known_failures, :suites
 
     def initialize
       @suite = :all
       @suites = nil
       @filter = nil
       @verbose = false
       @strict_only = false
-      @features = [:core]
+      @missing_features = []
       @known_failures = []
-      expand_features!
     end
 
     # Set multiple suites to run (overrides suite)
     def suites=(list)
       @suites = Array(list).map(&:to_sym)
     end
 
-    def features=(list)
-      @features = Array(list).map(&:to_sym)
-      expand_features!
+    def missing_features=(list)
+      @missing_features = Array(list).map(&:to_sym)
     end
 
     def known_failures=(list)
       @known_failures = Array(list).map(&:to_s)
     end
 
-    def feature?(name)
-      @features.include?(name.to_sym)
-    end
-
-    private
-
-    def expand_features!
-      FEATURE_EXPANSIONS.each do |feature, includes|
-        if @features.include?(feature)
-          @features |= includes
-        end
-      end
+    def missing_feature?(name)
+      @missing_features.include?(name.to_sym)
     end
   end
 
@@ -140,8 +118,8 @@ def configure
       @config
     end
 
-    def features
-      @config&.instance_variable_get(:@features) || DEFAULT_FEATURES
+    def missing_features
+      @config&.instance_variable_get(:@missing_features) || []
     end
 
     # Declare Ruby flags this adapter needs (e.g. "--yjit").

lib/liquid/spec/cli/features.rb

@@ -117,10 +117,10 @@ def self.run(args)
           puts "liquid-spec Features"
           puts "=" * 60
           puts
-          puts "Features control which specs are run. Declare them in your adapter:"
+          puts "Features are tags on specs. Declare what your adapter can't run:"
           puts
           puts "  LiquidSpec.configure do |config|"
-          puts "    config.features = [:core, :strict_parsing]"
+          puts "    config.missing_features = [:shopify_tags, :shopify_filters]"
           puts "  end"
           puts
           puts "-" * 60
@@ -147,8 +147,8 @@ def self.run(args)
             puts "    #{feature}: #{count}"
           end
           puts
-          puts "Recommended starter config:"
-          puts "  config.features = [:core, :strict_parsing]"
+          puts "Adapter with no limitations (runs all specs):"
+          puts "  config.missing_features = []"
           puts
         end
 
@@ -167,9 +167,9 @@ def self.count_specs_by_feature
               specs.each do |spec|
                 next unless spec.is_a?(Hash)
 
-                # Get required features from spec or metadata
-                features = spec["required_features"] ||
-                           (metadata && metadata["required_features"]) ||
+                # Get features from spec or metadata
+                features = spec["features"] ||
+                           (metadata && metadata["features"]) ||
                            []
 
                 features = [features] unless features.is_a?(Array)