Support providing a custom ERB parser class

USAGE.md

@@ -67,6 +67,27 @@ Packwerk reads from the `packwerk.yml` configuration file in the root directory.
 | load_paths           | All application autoload paths            | list of load paths |
 | custom_associations  | N/A                                       | list of custom associations, if any |
 
+### Using a custom ERB parser
+
+You can specify a custom ERB parser if needed. For example, if you're using `<%graphql>` tags from https://github.com/github/graphql-client in your ERBs, you can use a custom parser subclass to comment them out so that Packwerk can parse the rest of the file:
+
+```ruby
+class CustomParser < Packwerk::Parsers::Erb
+  def parse_buffer(buffer, file_path:)
+    preprocessed_source = buffer.source
+
+    # Comment out <%graphql ... %> tags. They won't contain any object
+    # references anyways.
+    preprocessed_source = preprocessed_source.gsub(/<%graphql/, "<%#")
+
+    preprocessed_buffer = Parser::Source::Buffer.new(file_path)
+    preprocessed_buffer.source = preprocessed_source
+    super(preprocessed_buffer, file_path: file_path)
+  end
+end
+
+Packwerk::Parsers::Factory.instance.erb_parser_class = CustomParser
+```
 
 ### Inflections
 

lib/packwerk/parsers/erb.rb

@@ -19,6 +19,10 @@ def initialize(parser_class: BetterHtml::Parser, ruby_parser: Ruby.new)
       def call(io:, file_path: "<unknown>")
         buffer = Parser::Source::Buffer.new(file_path)
         buffer.source = io.read
+        parse_buffer(buffer, file_path: file_path)
+      end
+
+      def parse_buffer(buffer, file_path:)
         parser = @parser_class.new(buffer, template_language: :html)
         to_ruby_ast(parser.ast, file_path)
       rescue EncodingError => e

lib/packwerk/parsers/factory.rb

@@ -26,9 +26,18 @@ def for_path(path)
         when RUBY_REGEX
           @ruby_parser ||= Ruby.new
         when ERB_REGEX
-          @erb_parser ||= Erb.new
+          @erb_parser ||= erb_parser_class.new
         end
       end
+
+      def erb_parser_class
+        @erb_parser_class || Erb
+      end
+
+      def erb_parser_class=(klass)
+        @erb_parser_class = klass
+        @erb_parser = nil
+      end
     end
   end
 end

test/unit/parsers/factory_test.rb

@@ -23,6 +23,11 @@ class FactoryTest < Minitest::Test
         assert_instance_of(Parsers::Erb, factory.for_path("foo.html.erb"))
         assert_instance_of(Parsers::Erb, factory.for_path("foo.md.erb"))
         assert_instance_of(Parsers::Erb, factory.for_path("/sub/directory/foo.erb"))
+
+        fake_class = Class.new
+        with_erb_parser_class(fake_class) do
+          assert_instance_of(fake_class, factory.for_path("foo.html.erb"))
+        end
       end
 
       test "#for_path gives nil for unknown path" do
@@ -33,6 +38,13 @@ class FactoryTest < Minitest::Test
 
       private
 
+      def with_erb_parser_class(klass)
+        factory.erb_parser_class = klass
+        yield
+      ensure
+        factory.erb_parser_class = nil
+      end
+
       def factory
         Parsers::Factory.instance
       end