Add ThrowingErrorListener to Python ANTLR4 parser to match JavaScript behavior (#110)

* Initial plan

* Add ThrowingErrorListener to Python ANTLR4 parser matching JavaScript implementation

Co-authored-by: hzhangxyz <[email protected]>

* Improve error tests to use pytest.raises for better test structure

Co-authored-by: hzhangxyz <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: hzhangxyz <[email protected]>

Author: Copilot

bnf/apyds_bnf/__init__.py

@@ -1,6 +1,7 @@
 __all__ = ["parse", "unparse"]
 
 from antlr4 import InputStream, CommonTokenStream
+from antlr4.error.ErrorListener import ErrorListener
 from .DspLexer import DspLexer
 from .DspParser import DspParser
 from .DspVisitor import DspVisitor
@@ -9,6 +10,11 @@
 from .DsVisitor import DsVisitor
 
 
+class ThrowingErrorListener(ErrorListener):
+    def syntaxError(self, recognizer, offendingSymbol, line, column, msg, e):
+        raise Exception(f"line {line}:{column} {msg}")
+
+
 class ParseVisitor(DspVisitor):
     def visitRule_pool(self, ctx):
         return "\n\n".join(self.visit(r) for r in ctx.rule_())
@@ -71,8 +77,12 @@ def visitBinary(self, ctx):
 def parse(input: str) -> str:
     chars = InputStream(input)
     lexer = DspLexer(chars)
+    lexer.removeErrorListeners()
+    lexer.addErrorListener(ThrowingErrorListener())
     tokens = CommonTokenStream(lexer)
     parser = DspParser(tokens)
+    parser.removeErrorListeners()
+    parser.addErrorListener(ThrowingErrorListener())
     tree = parser.rule_pool()
     visitor = ParseVisitor()
     return visitor.visit(tree)
@@ -81,8 +91,12 @@ def parse(input: str) -> str:
 def unparse(input: str) -> str:
     chars = InputStream(input)
     lexer = DsLexer(chars)
+    lexer.removeErrorListeners()
+    lexer.addErrorListener(ThrowingErrorListener())
     tokens = CommonTokenStream(lexer)
     parser = DsParser(tokens)
+    parser.removeErrorListeners()
+    parser.addErrorListener(ThrowingErrorListener())
     tree = parser.rule_pool()
     visitor = UnparseVisitor()
     return visitor.visit(tree)

bnf/tests/test_parse_unparse.py

@@ -1,3 +1,4 @@
+import pytest
 from apyds_bnf import parse, unparse
 
 
@@ -143,3 +144,38 @@ def test_roundtrip_unparse_parse() -> None:
     dsp_intermediate = unparse(ds_original)
     ds_result = parse(dsp_intermediate)
     assert ds_result == ds_original
+
+
+def test_parse_error_missing_closing_parenthesis() -> None:
+    """Test that parse throws error on missing closing parenthesis"""
+    dsp_input = "(a + b -> c"
+    with pytest.raises(Exception, match=r"line 1:7.*no viable alternative"):
+        parse(dsp_input)
+
+
+def test_parse_error_bad_syntax() -> None:
+    """Test that parse throws error on bad syntax"""
+    dsp_input = "a b c -> -> d"
+    with pytest.raises(Exception, match=r"line 1:2.*mismatched input"):
+        parse(dsp_input)
+
+
+def test_parse_error_malformed_parentheses() -> None:
+    """Test that parse throws error on malformed parentheses"""
+    dsp_input = "()()()"
+    with pytest.raises(Exception, match=r"line 1:1.*no viable alternative"):
+        parse(dsp_input)
+
+
+def test_unparse_error_incomplete_binary() -> None:
+    """Test that unparse throws error on incomplete binary expression"""
+    ds_input = "(binary"
+    with pytest.raises(Exception, match=r"line 1:7.*mismatched input"):
+        unparse(ds_input)
+
+
+def test_unparse_error_malformed_function() -> None:
+    """Test that unparse throws error on malformed function"""
+    ds_input = "(function"
+    with pytest.raises(Exception, match=r"line 1:9.*mismatched input"):
+        unparse(ds_input)