Fixes parsing of ERB comments without a space

The ERB parser we're using misparses comments of the form:

    <%# ... #>

(no space between % and #)

With a space the AST is:

    s(:erb, nil, nil,
      s(:code, " # this should not fail: ' "), nil)

Without a space the AST is:

    s(:erb,
      s(:indicator, "#"), nil,
      s(:code, " this should not fail: ' "), nil)

The latter AST causes a crash when parsing the `:code` node as Ruby.

Works around the issue by transforming the latter AST to the former.

Fixes #429

lib/i18n/tasks/scanners/erb_ast_processor.rb

@@ -35,7 +35,10 @@ def on_code(node)
       node
     end
 
+    # @param node [::Parser::AST::Node]
+    # @return [::Parser::AST::Node]
     def handler_missing(node)
+      node = transform_misparsed_comment(node)
       node.updated(
         nil,
         node.children.map { |child| node?(child) ? process(child) : child }
@@ -44,6 +47,35 @@ def handler_missing(node)
 
     private
 
+    # Works around incorrect handling of comments of the form:
+    # <%# ... #>
+    # (no space between % and #)
+    #
+    # With a space the AST is:
+    #
+    #     s(:erb, nil, nil,
+    #       s(:code, " # this should not fail: ' "), nil)
+    #
+    # Without a space the AST is:
+    #
+    #     s(:erb,
+    #       s(:indicator, "#"), nil,
+    #       s(:code, " this should not fail: ' "), nil)
+    # @param node [::Parser::AST::Node]
+    # @return [::Parser::AST::Node]
+    def transform_misparsed_comment(node)
+      return node unless node.type == :erb && node.children.size == 4 &&
+        node.children[0]&.type == :indicator && node.children[0].children[0] == "#" &&
+        node.children[1].nil? &&
+        node.children[2]&.type == :code &&
+        node.children[3].nil?
+      code_node = node.children[2]
+      node.updated(
+        nil,
+        [nil, nil, code_node.updated(nil, ["##{code_node.children[0]}"]), nil]
+      )
+    end
+
     def node?(node)
       node.is_a?(::Parser::AST::Node)
     end

spec/fixtures/used_keys/app/views/application/show.html.erb

@@ -21,4 +21,6 @@ I18n.t("this_should_not")
 
     <%= render Blacklight::Document::CitationComponent.with_collection(@documents) if @documents.present? %>
   <% end %>
+
+  <%# this should not fail: ' %>
 </h3>