PrismScanner: Contextual parsing for Rails

Adds a scanner that supports:
  - `before_action` in controllers
  - translations in nested method calls
  - `model_name.human`
  - `human_attribute_name`

CHANGES.md

@@ -2,6 +2,8 @@
 
 * Uses AST-parser for all ERB-files, not just `.html.erb`
 * [Fixed regex in `PatternScanner`] (https://github.com/glebm/i18n-tasks/issues/572)
+* Adds contextual parser to support more Rails-translations
+  [#565](https://github.com/glebm/i18n-tasks/pull/565)
 
 ## v1.0.14
 

README.md

@@ -506,6 +506,30 @@ OPENAI_API_KEY=<OpenAI API key>
 OPENAI_MODEL=<optional>
 ```
 
+### Contextual Rails Parser
+
+There is an experimental feature to parse Rails with more context. `i18n-tasks` will support:
+- Translations called in `before_actions`
+- Translations called in nested methods
+- `Model.human_attribute_name` calls
+- `Model.model_name.human` calls
+
+Enabled it by adding the scanner in your `config/i18n-tasks.yml`:
+
+```ruby
+<% I18n::Tasks.add_scanner( 
+  'I18n::Tasks::Scanners::PrismScanner',
+  only: %w(*.rb)
+) %>
+```
+
+To only enable Ruby-scanning and not any Rails support, please add config under the `search` section:
+
+```yaml
+search:
+  prism_visitor: "ruby" # default "rails"
+```
+
 ## Interactive console
 
 `i18n-tasks irb` starts an IRB session in i18n-tasks context. Type `guide` for more information.

lib/i18n/tasks/scanners/prism_scanner.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require_relative 'file_scanner'
+require_relative 'ruby_ast_scanner'
+
+module I18n::Tasks::Scanners
+  class PrismScanner < FileScanner
+    def initialize(**args)
+      unless RAILS_VISITOR || RUBY_VISITOR
+        warn(
+          'Please make sure `prism` is available to use this feature. Fallback to Ruby AST Scanner.'
+        )
+      end
+      super
+
+      @visitor_class = config[:prism_visitor] == 'ruby' ? RUBY_VISITOR : RAILS_VISITOR
+      @fallback = RubyAstScanner.new(**args)
+    end
+
+    protected
+
+    # Extract all occurrences of translate calls from the file at the given path.
+    #
+    # @return [Array<[key, Results::KeyOccurrence]>] each occurrence found in the file
+    def scan_file(path)
+      return @fallback.send(:scan_file, path) if @visitor_class.nil?
+
+      process_prism_parse_result(
+        path,
+        PARSER.parse_file(path).value,
+        PARSER.parse_file_comments(path)
+      )
+    rescue Exception => e # rubocop:disable Lint/RescueException
+      raise(
+        ::I18n::Tasks::CommandError.new(
+          e,
+          "Error scanning #{path}: #{e.message}"
+        )
+      )
+    end
+
+    def process_prism_parse_result(path, parsed, comments = nil)
+      return @fallback.send(:scan_file, path) if RUBY_VISITOR.skip_prism_comment?(comments)
+
+      visitor = @visitor_class.new(comments: comments)
+      nodes = parsed.accept(visitor)
+
+      nodes
+        .filter_map do |node|
+          next node.occurrences(path) if node.is_a?(I18n::Tasks::Scanners::PrismScanners::TranslationNode)
+          next unless node.respond_to?(:translation_nodes)
+
+          node.translation_nodes.flat_map { |n| n.occurrences(path) }
+        end
+        .flatten(1)
+    end
+
+    # This block handles adding a fallback if the `prism` gem is not available.
+    begin
+      require 'prism'
+      require_relative 'prism_scanners/rails_visitor'
+      require_relative 'prism_scanners/visitor'
+      PARSER = Prism
+      RUBY_VISITOR = I18n::Tasks::Scanners::PrismScanners::Visitor
+      RAILS_VISITOR = I18n::Tasks::Scanners::PrismScanners::RailsVisitor
+    rescue LoadError
+      PARSER = nil
+      RUBY_VISITOR, RAILS_VISITOR = nil
+    end
+  end
+end