Contextual parsing of Rails controllers

- Adding a Parser based on [Prism](https://github.com/ruby/prism).
- It handles all parsing and matching of the keys, currently it is not
  connected to the used_keys flow but only done as an experiment.

lib/i18n/tasks/scanners/prism_rails_controller_parser.rb

@@ -0,0 +1,265 @@
+# frozen_string_literal: true
+
+require 'prism'
+require 'i18n/tasks/scanners/results/key_occurrences'
+
+module I18n::Tasks::Scanners
+  class PrismRailsControllerParser
+    DOT = '.'
+
+    def process_path(path)
+      parse_results = Prism.parse_file(path)
+
+      visitor = PrismControllerVisitor.new
+
+      parse_results.value.accept(visitor)
+
+      visitor.translation_calls(path)
+    end
+
+    class TranslationNode
+      attr_reader(:key, :node)
+
+      def initialize(node:, key:, options: nil)
+        @node = node
+        @key = key
+        @options = options
+      end
+
+      def type
+        :translation_node
+      end
+
+      def location
+        @node.location
+      end
+
+      def relative_key?
+        @key.start_with?(DOT)
+      end
+
+      def to_occurrence(path, controller_key, method, node)
+        location = node.location
+
+        final_key = full_key(controller_key, method)
+        return nil if final_key.nil?
+
+        [
+          final_key,
+          ::I18n::Tasks::Scanners::Results::Occurrence.new(
+            path: path,
+            line: node.node.slice,
+            pos: location.start_offset,
+            line_pos: location.start_column,
+            line_num: location.start_line,
+            raw_key: key
+          )
+        ]
+      end
+
+      def full_key(controller_key, method)
+        return nil if relative_key? && method[:private]
+        return key unless relative_key?
+
+        # We should handle fallback to key without method name
+        [controller_key, method[:name], key].compact.join(DOT).gsub("..", ".")
+      end
+    end
+
+    class PrismControllerVisitor < Prism::Visitor
+      def initialize
+        @controller_node_path = []
+        @private_methods = false
+        @methods = {}
+        @before_actions = {}
+
+        super
+      end
+
+      def controller_key
+        @controller_node_path.flat_map do |node|
+          case node.type
+          when :module_node
+            node.name.to_s.underscore
+          when :class_node
+            node.constant_path.child_nodes.map do |node|
+              node.name.to_s.underscore.sub(/_controller\z/, '')
+            end
+          end
+        end
+      end
+
+      def translation_calls(path)
+        process_before_actions
+        process_methods(path)
+      end
+
+      def visit_module_node(node)
+        previous_location = @controller_node_path.last&.location
+        if previous_location && previous_location.end_offset < node.location.start_offset
+          @controller_node_path = [node]
+        else
+          @controller_node_path << node
+        end
+
+        super
+      end
+
+      def visit_class_node(node)
+        @controller_node_path << node
+        super
+      end
+
+      def visit_def_node(node)
+        translation_calls, other_calls = node.body.child_nodes
+          .filter_map {|n| visit(n) }
+          .partition { |n| n.type == :translation_node }
+
+        @methods[node.name] = {
+          name: node.name,
+          private: @private_methods,
+          translation_calls: translation_calls,
+          other_calls: other_calls
+        }
+
+        super
+      end
+
+      def visit_call_node(node)
+        case node.name
+        when :private
+          @private_methods = true
+        when :before_action
+          parse_before_action(node)
+        when :t, :'I18n.t', :t!, :'I18n.t!', :translate, :translate!
+          key_argument, options = node.arguments.arguments
+          TranslationNode.new(
+            node: node,
+            key: extract_value(key_argument),
+            options: options
+          )
+        else
+          node
+        end
+      end
+
+      private
+
+      def process_before_actions
+        methods = @methods.values
+        private_methods = methods.select { |m| m[:private] }
+        non_private_methods = methods.reject { |m| m[:private] }
+
+        @before_actions.each do |name, before_action|
+          # We can only handle before_actions that are private methods
+          before_action_method = private_methods.find { |m| m[:name].to_s == name }
+          next if before_action_method.nil?
+
+          methods_for_before_action(
+            non_private_methods,
+            before_action
+          ).each do |method|
+            method[:translation_calls] += before_action_method[:translation_calls]
+            method[:other_calls] += before_action_method[:other_calls]
+          end
+        end
+      end
+
+      def process_methods(path)
+        @methods.each_value do |method|
+          process_method(method)
+        end
+
+        @methods.values.flat_map do |method|
+          method[:translation_calls].map do |node|
+            node.to_occurrence(path, controller_key, method, node)
+          end.compact
+        end
+      end
+
+      def process_method(method)
+        return if method[:status] == :processed
+        fail(ArgumentError, 'Cannot handle cyclic method calls') if method[:status] == :processing
+
+        method[:status] = :processing
+
+        method[:other_calls].each do |call_node|
+          process_method(@methods[call_node.name])
+          method[:translation_calls] += Array(@methods[call_node.name][:translation_calls])
+        end
+
+        method[:status] = :processed
+      end
+
+      def parse_before_action(node)
+        arguments_node = node.arguments
+        if arguments_node.arguments.empty? || arguments_node.arguments.size > 2
+          fail(ArgumentError, 'Cannot handle before_action with these arguments')
+        end
+
+        name = extract_value(arguments_node.arguments[0])
+        options = arguments_node.arguments.last if arguments_node.arguments.length > 1
+
+        @before_actions[name] = {
+          node: node,
+          only: Array(extract_hash_value(options, :only)),
+          except: Array(extract_hash_value(options, :except)),
+          calls: []
+        }
+      end
+
+      def extract_hash_value(node, key)
+        return unless %i[keyword_hash_node hash_node].include?(node.type)
+
+        node.elements.each do |element|
+          next unless key.to_s == element.key.value.to_s
+
+          return extract_value(element.value)
+        end
+
+        nil
+      end
+
+      def extract_value(node)
+        case node.type
+        when :symbol_node
+          node.value.to_s
+        when :string_node
+          node.content
+        when :array_node
+          node.child_nodes.map { |child| extract_value(child) }
+        else
+          fail(ArgumentError, "Cannot handle node type: #{node.type}")
+        end
+      end
+
+      def methods_for_before_action(methods, before_action)
+        if before_action[:only].present?
+          methods.select { |m| before_action[:only].include?(m[:name]) }
+        elsif before_action[:except].present?
+          methods.reject { |m| before_action[:except].include?(m[:name]) }
+        end
+      end
+
+      def key_from_node(node)
+        @matchers.each do |matcher|
+          result =
+            if matcher.respond_to?(:process_node)
+              matcher.process_node(node)
+            else
+              matcher.convert_to_key_occurrences(node, nil)
+            end
+          next if result.nil?
+
+          return result[0]
+        end
+
+        nil
+      end
+
+      def relative_key?(key)
+        key.start_with?(DOT)
+      end
+    end
+  end
+end

spec/fixtures/used_keys/app/controllers/events_controller.rb

@@ -1,7 +1,32 @@
+# frozen_string_literal: true
+
 class EventsController < ApplicationController
+  before_action(:method_in_before_action, only: :create)
+  before_action('method_in_before_action2', except: %i[create])
+
   def create
-    t(".relative_key")
-    t("absolute_key")
-    I18n.t("very_absolute_key")
+    t('.relative_key')
+    t('absolute_key')
+    I18n.t('very_absolute_key')
+    method_a
+  end
+
+  def not_an_action
+    t('.relative_key')
+    method_a
+  end
+
+  private
+
+  def method_a
+    t('.success')
+  end
+
+  def method_in_before_action
+    t('.before_action')
+  end
+
+  def method_in_before_action2
+    t('.before_action2')
   end
 end

spec/scanners/prism_rails_controller_parser_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'i18n/tasks/scanners/prism_rails_controller_parser'
+
+RSpec.describe 'PrismRailsControllerParser' do
+  describe '#process - controller' do
+    it 'finds translations' do
+      path = "spec/fixtures/used_keys/app/controllers/events_controller.rb"
+      processor = I18n::Tasks::Scanners::PrismRailsControllerParser.new
+      results = processor.process_path(path)
+
+      expect(results.size).to eq(8)
+    end
+  end
+end