Port liquid-c bug compatible whitespace trimming (#1291)

lib/liquid/block_body.rb

@@ -145,7 +145,11 @@ module Liquid
       if token[2] == WhitespaceControl
         previous_token = @nodelist.last
         if previous_token.is_a?(String)
+          first_byte = previous_token.getbyte(0)
           previous_token.rstrip!
+          if previous_token.empty? && parse_context[:bug_compatible_whitespace_trimming] && first_byte
+            previous_token << first_byte
+          end
         end
       end
       parse_context.trim_whitespace = (token[-3] == WhitespaceControl)

test/integration/trim_mode_test.rb

@@ -528,4 +528,32 @@ class TrimModeTest < Minitest::Test
     END_EXPECTED
     assert_template_result(expected, text)
   end
+
+  def test_pre_trim_blank_preceding_text
+    template = Liquid::Template.parse("\n{%- raw %}{% endraw %}")
+    assert_equal("", template.render)
+
+    template = Liquid::Template.parse("\n{%- if true %}{% endif %}")
+    assert_equal("", template.render)
+
+    template = Liquid::Template.parse("{{ 'B' }} \n{%- if true %}C{% endif %}")
+    assert_equal("BC", template.render)
+  end
+
+  def test_bug_compatible_pre_trim
+    template = Liquid::Template.parse("\n {%- raw %}{% endraw %}", bug_compatible_whitespace_trimming: true)
+    assert_equal("\n", template.render)
+
+    template = Liquid::Template.parse("\n {%- if true %}{% endif %}", bug_compatible_whitespace_trimming: true)
+    assert_equal("\n", template.render)
+
+    template = Liquid::Template.parse("{{ 'B' }} \n{%- if true %}C{% endif %}", bug_compatible_whitespace_trimming: true)
+    assert_equal("B C", template.render)
+
+    template = Liquid::Template.parse("B\n {%- raw %}{% endraw %}", bug_compatible_whitespace_trimming: true)
+    assert_equal("B", template.render)
+
+    template = Liquid::Template.parse("B\n {%- if true %}{% endif %}", bug_compatible_whitespace_trimming: true)
+    assert_equal("B", template.render)
+  end
 end # TrimModeTest