Fix stix2.pattern_visitor.create_pattern_object() so its

documentation at least isn't wrong, and it behaves better.

stix2/pattern_visitor.py

@@ -1,16 +1,15 @@
 import importlib
 import inspect
 
-from antlr4 import CommonTokenStream, InputStream
-from antlr4.tree.Trees import Trees
+from antlr4 import BailErrorStrategy, CommonTokenStream, InputStream
+import antlr4.error.Errors
 import six
-from stix2patterns.exceptions import ParseException
+from stix2patterns.exceptions import ParseException, ParserErrorListener
 from stix2patterns.grammars.STIXPatternLexer import STIXPatternLexer
 from stix2patterns.grammars.STIXPatternParser import (
     STIXPatternParser, TerminalNode,
 )
 from stix2patterns.grammars.STIXPatternVisitor import STIXPatternVisitor
-from stix2patterns.validator import STIXPatternErrorListener
 
 from .patterns import *
 from .patterns import _BooleanExpression
@@ -328,20 +327,12 @@ class STIXPatternVisitorForSTIX2(STIXPatternVisitor):
 
 def create_pattern_object(pattern, module_suffix="", module_name=""):
     """
-    Validates a pattern against the STIX Pattern grammar.  Error messages are
-    returned in a list.  The test passed if the returned list is empty.
+    Create a STIX pattern AST from a pattern string.
     """
 
-    start = ''
-    if isinstance(pattern, six.string_types):
-        start = pattern[:2]
-        pattern = InputStream(pattern)
+    pattern = InputStream(pattern)
 
-    if not start:
-        start = pattern.readline()[:2]
-        pattern.seek(0)
-
-    parseErrListener = STIXPatternErrorListener()
+    parseErrListener = ParserErrorListener()
 
     lexer = STIXPatternLexer(pattern)
     # it always adds a console listener by default... remove it.
@@ -350,6 +341,7 @@ def create_pattern_object(pattern, module_suffix="", module_name=""):
     stream = CommonTokenStream(lexer)
 
     parser = STIXPatternParser(stream)
+    parser._errHandler = BailErrorStrategy()
 
     parser.buildParseTrees = True
     # it always adds a console listener by default... remove it.
@@ -363,6 +355,15 @@ def create_pattern_object(pattern, module_suffix="", module_name=""):
         if lit_name == u"<INVALID>":
             parser.literalNames[i] = parser.symbolicNames[i]
 
-    tree = parser.pattern()
+    try:
+        tree = parser.pattern()
+    except antlr4.error.Errors.ParseCancellationException as e:
+        real_exc = e.args[0]
+        parser._errHandler.reportError(parser, real_exc)
+        six.raise_from(
+            ParseException(parseErrListener.error_message),
+            real_exc,
+        )
+
     builder = STIXPatternVisitorForSTIX2(module_suffix, module_name)
     return builder.visit(tree)