[Bug] Ensure grammar.match raises appropriately on incomplete input (…

…#1016)

Force-feed `ByteParser` an EOS token if it's not done by the time all
input has been consumed. This lets us raise an exception when a string
fails to complete a grammar

guidance/_grammar.py

@@ -177,6 +177,8 @@ def match(
 
         try:
             parser.consume_bytes(byte_string)
+            if not allow_partial:
+                parser.force_done()
         except _parser.ByteParserException:
             if raise_exceptions:
                 raise

tests/unit/test_grammar.py

@@ -1,6 +1,7 @@
 import pytest
 import guidance
 from guidance import gen, models, optional, select, string
+from guidance._parser import ByteParserException
 
 
 def test_select_reset_pos():
@@ -132,4 +133,12 @@ def test_partial_match(self, string):
         match = g.match(f"123{string}", allow_partial=True)
         assert match is not None
         assert match.partial
-        assert match.captures["mycap"] == string
+        assert match.captures["mycap"] == string
+
+    def test_raises_on_incomplete_input(self):
+        g = "123" + gen(regex=r"\d+x?", name="mycap")
+        # Ok since we allow partial
+        assert g.match(b"123", raise_exceptions=True, allow_partial=True) is not None
+        # Shold raise since we don't allow partial
+        with pytest.raises(ByteParserException):
+            g.match(b"123", raise_exceptions=True)