Don't parse YAML twice

Earlopain · bbatsov · commit c2ae36230d3f · 2024-09-04T07:40:53.000+03:00
Once for the duplication check, and once again to convert it to a ruby hash

We can instead use the yaml ast from the duplication check and convert
that into a hash directly.

```
# Rubocop
# Base:
$ hyperfine -w 5 -r 20 "bundle exec rubocop Rakefile"
Benchmark 1: bundle exec rubocop Rakefile
  Time (mean ± σ):      1.041 s ±  0.014 s    [User: 0.898 s, System: 0.140 s]
  Range (min … max):    1.013 s …  1.061 s    20 runs

# Patch:
$ hyperfine -w 5 -r 20 "bundle exec rubocop Rakefile"
Benchmark 1: bundle exec rubocop Rakefile
  Time (mean ± σ):      1.013 s ±  0.008 s    [User: 0.865 s, System: 0.146 s]
  Range (min … max):    0.998 s …  1.027 s    20 runs
```

~2.7%  Faster

```
# Gitlab
# Base:
$ hyperfine -w 5 -r 20 "bundle exec rubocop Rakefile"
Benchmark 1: bundle exec rubocop Rakefile
  Time (mean ± σ):      3.485 s ±  0.027 s    [User: 2.565 s, System: 0.909 s]
  Range (min … max):    3.445 s …  3.529 s    20 runs

# Applied:
$ hyperfine -w 5 -r 20 "bundle exec rubocop Rakefile"
Benchmark 1: bundle exec rubocop Rakefile
  Time (mean ± σ):      3.401 s ±  0.029 s    [User: 2.483 s, System: 0.906 s]
  Range (min … max):    3.356 s …  3.466 s    20 runs
```

~2.5% faster. I expected more since they have so many config files but hey, still something.
diff --git a/lib/rubocop/config_loader.rb b/lib/rubocop/config_loader.rb
@@ -67,8 +67,8 @@ def load_file(file, check: true)
       def load_yaml_configuration(absolute_path)
         file_contents = read_file(absolute_path)
         yaml_code = Dir.chdir(File.dirname(absolute_path)) { ERB.new(file_contents).result }
-        check_duplication(yaml_code, absolute_path)
-        hash = yaml_safe_load(yaml_code, absolute_path) || {}
+        yaml_tree = check_duplication(yaml_code, absolute_path)
+        hash = yaml_tree_to_hash(yaml_tree) || {}
 
         puts "configuration from #{absolute_path}" if debug?
 
@@ -235,8 +235,8 @@ def read_file(absolute_path)
         raise ConfigNotFoundError, "Configuration file not found: #{absolute_path}"
       end
 
-      def yaml_safe_load(yaml_code, filename)
-        yaml_safe_load!(yaml_code, filename)
+      def yaml_tree_to_hash(yaml_tree)
+        yaml_tree_to_hash!(yaml_tree)
       rescue ::StandardError
         if defined?(::SafeYAML)
           raise 'SafeYAML is unmaintained, no longer needed and should be removed'
@@ -245,10 +245,16 @@ def yaml_safe_load(yaml_code, filename)
         raise
       end
 
-      def yaml_safe_load!(yaml_code, filename)
-        YAML.safe_load(
-          yaml_code, permitted_classes: [Regexp, Symbol], aliases: true, filename: filename
-        )
+      def yaml_tree_to_hash!(yaml_tree)
+        return nil unless yaml_tree
+
+        # Optimization: Because we checked for duplicate keys, we already have the
+        # yaml tree and don't need to parse it again.
+        # Also see https://github.com/ruby/psych/blob/v5.1.2/lib/psych.rb#L322-L336
+        class_loader = YAML::ClassLoader::Restricted.new(%w[Regexp Symbol], [])
+        scanner = YAML::ScalarScanner.new(class_loader)
+        visitor = YAML::Visitors::ToRuby.new(scanner, class_loader)
+        visitor.accept(yaml_tree)
       end
     end
 
diff --git a/lib/rubocop/yaml_duplication_checker.rb b/lib/rubocop/yaml_duplication_checker.rb
@@ -16,6 +16,7 @@ def self.check(yaml_string, filename, &on_duplicated)
       return unless tree
 
       traverse(tree, &on_duplicated)
+      tree
     end
 
     def self.traverse(tree, &on_duplicated)
diff --git a/spec/rubocop/config_loader_spec.rb b/spec/rubocop/config_loader_spec.rb
@@ -1768,6 +1768,32 @@ def self.inject!
       expect(configuration.to_h).to eq({})
     end
 
+    it 'rejects non-allowed yaml types' do
+      create_file(configuration_path, <<~YAML)
+        foo: !ruby/object:Rational
+          numerator: 1
+          denominator: 2
+      YAML
+
+      expect { load_file }.to raise_error(Psych::DisallowedClass, /Rational/)
+    end
+
+    it 'allows yaml anchors' do
+      create_file(configuration_path, <<~YAML)
+        Style/Alias: &anchor
+          Enabled: false
+        Style/Encoding:
+          <<: *anchor
+      YAML
+
+      expect(load_file.to_h).to eq(
+        {
+          'Style/Alias' => { 'Enabled' => false },
+          'Style/Encoding' => { 'Enabled' => false }
+        }
+      )
+    end
+
     context 'set neither true nor false to value to Enabled' do
       before do
         create_file(configuration_path, <<~YAML)
