fix parsing quirky incomplete expressions

lib/liquid/lexer.rb

@@ -181,7 +181,7 @@ module Liquid
             @output << DOTDOT
           elsif special == DASH
             # Special case for negative numbers
-            if NUMBER_TABLE[@ss.peek_byte]
+            if !@ss.eos? && NUMBER_TABLE[@ss.peek_byte]
               @ss.pos -= 1
               @output << [:number, @ss.scan(NUMBER_LITERAL)]
             else
@@ -192,7 +192,7 @@ module Liquid
           end
         elsif (sub_table = TWO_CHARS_COMPARISON_JUMP_TABLE[peeked])
           @ss.scan_byte
-          if (found = sub_table[@ss.peek_byte])
+          if !@ss.eos? && (found = sub_table[@ss.peek_byte])
             @output << found
             @ss.scan_byte
           else
@@ -200,7 +200,7 @@ module Liquid
           end
         elsif (sub_table = COMPARISON_JUMP_TABLE[peeked])
           @ss.scan_byte
-          if (found = sub_table[@ss.peek_byte])
+          if !@ss.eos? && (found = sub_table[@ss.peek_byte])
             @output << found
             @ss.scan_byte
           else

test/integration/parsing_quirks_test.rb

@@ -131,4 +131,16 @@ class ParsingQuirksTest < Minitest::Test
   def test_contains_in_id
     assert_template_result(' YES ', '{% if containsallshipments == true %} YES {% endif %}', { 'containsallshipments' => true })
   end
+
+  def test_incomplete_expression
+    with_error_mode(:lax) do
+      assert_template_result("false", "{% liquid assign foo = false -\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false >\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false <\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false =\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false !\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false 1\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false a\n%}{{ foo }}")
+    end
+  end
 end # ParsingQuirksTest

test/unit/lexer_unit_test.rb

@@ -102,4 +102,11 @@ class LexerUnitTest < Minitest::Test
       Lexer.new("a.contains.b").tokenize,
     )
   end
+
+  def test_tokenize_incomplete_expression
+    assert_equal([[:id, "false"], [:dash, "-"], [:end_of_string]], Lexer.new("false -").tokenize)
+    assert_equal([[:id, "false"], [:comparison, "<"], [:end_of_string]], Lexer.new("false <").tokenize)
+    assert_equal([[:id, "false"], [:comparison, ">"], [:end_of_string]], Lexer.new("false >").tokenize)
+    assert_equal([[:id, "false"], [:number, "1"], [:end_of_string]], Lexer.new("false 1").tokenize)
+  end
 end