Move parse_expression to Parser.unsafe_parse_expression

- Add Parser#string
- Add Parser#unsafe_parse_expression
- Add private Parser#parse_expression
- Remove ParseContext.parse_expression
- Remove Tag.parse_expression
- Condition.parse_expression now takes a parser as argument

test/unit/condition_unit_test.rb

@@ -166,25 +166,24 @@ class ConditionUnitTest < Minitest::Test
     assert_includes(err.lines.map(&:strip), expected)
   end
 
-  def test_parse_expression_with_safe_true
+  def test_parse_expression
     environment = Environment.build
     parse_context = ParseContext.new(environment: environment)
-    result = Condition.parse_expression(parse_context, 'product.title', safe: true)
+    parser = parse_context.new_parser('product.title')
+    result = Condition.parse_expression(parser)
 
     assert_instance_of(VariableLookup, result)
     assert_equal('product', result.name)
     assert_equal(['title'], result.lookups)
   end
 
-  def test_parse_expression_raises_internal_error_if_not_safe
+  def test_parse_expression_returns_method_literal_for_blank_and_empty
     environment = Environment.build
     parse_context = ParseContext.new(environment: environment)
+    parser = parse_context.new_parser('blank')
+    result = Condition.parse_expression(parser)
 
-    error = assert_raises(Liquid::InternalError) do
-      Condition.parse_expression(parse_context, 'product.title')
-    end
-
-    assert_match(/unsafe parse_expression cannot be used/, error.message)
+    assert_instance_of(Condition::MethodLiteral, result)
   end
 
   # Tests for blank? comparison without ActiveSupport