refactor: Reduce maximum block nesting in Liquid::BlockBody#parse

.rubocop.yml

@@ -7,8 +7,6 @@ AllCops:
 
 Metrics/BlockNesting:
   Max: 3
-  Exclude:
-    - 'lib/liquid/block_body.rb'
 
 Metrics/ModuleLength:
   Enabled: false

lib/liquid/block_body.rb

@@ -15,26 +15,24 @@ module Liquid
     def parse(tokenizer, parse_context)
       parse_context.line_number = tokenizer.line_number
       while token = tokenizer.shift
-        unless token.empty?
+        next if token.empty?
         case
         when token.start_with?(TAGSTART)
           whitespace_handler(token, parse_context)
-            if token =~ FullToken
+          unless token =~ FullToken
+            raise_missing_tag_terminator(token, parse_context)
+          end
           tag_name = $1
           markup = $2
           # fetch the tag from registered blocks
-              if tag = registered_tags[tag_name]
+          unless tag = registered_tags[tag_name]
-                new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
-                @blank &&= new_tag.blank?
-                @nodelist << new_tag
-              else
             # end parsing if we reach an unknown tag and let the caller decide
             # determine how to proceed
             return yield tag_name, markup
           end
-            else
+          new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
-              raise_missing_tag_terminator(token, parse_context)
+          @blank &&= new_tag.blank?
-            end
+          @nodelist << new_tag
         when token.start_with?(VARSTART)
           whitespace_handler(token, parse_context)
           @nodelist << create_variable(token, parse_context)
@@ -47,7 +45,6 @@ module Liquid
           @nodelist << token
           @blank &&= !!(token =~ /\A\s*\z/)
         end
-        end
         parse_context.line_number = tokenizer.line_number
       end