Added 'considered_rules' to exceptions, to help users debug

lark/common.py

@@ -17,11 +17,12 @@ class ParseError(Exception):
     pass
 
 class UnexpectedToken(ParseError):
-    def __init__(self, token, expected, seq, index):
+    def __init__(self, token, expected, seq, index, considered_rules=None):
         self.token = token
         self.expected = expected
         self.line = getattr(token, 'line', '?')
         self.column = getattr(token, 'column', '?')
+        self.considered_rules = considered_rules
 
         try:
             context = ' '.join(['%r(%s)' % (t.value, t.type) for t in seq[index:index+5]])

lark/lexer.py

@@ -10,7 +10,7 @@ class LexError(Exception):
     pass
 
 class UnexpectedInput(LexError):
-    def __init__(self, seq, lex_pos, line, column, allowed=None):
+    def __init__(self, seq, lex_pos, line, column, allowed=None, considered_rules=None):
         context = seq[lex_pos:lex_pos+5]
         message = "No token defined for: '%s' in %r at line %d col %d" % (seq[lex_pos], context, line, column)
         if allowed:
@@ -22,6 +22,7 @@ class UnexpectedInput(LexError):
         self.column = column
         self.context = context
         self.allowed = allowed
+        self.considered_rules = considered_rules
 
 class Token(Str):
     def __new__(cls, type_, value, pos_in_stream=None, line=None, column=None):

lark/parsers/earley.py

@@ -197,7 +197,7 @@ class Parser:
 
             if not next_set:
                 expect = {i.expect for i in column.to_scan}
-                raise UnexpectedToken(token, expect, stream, i)
+                raise UnexpectedToken(token, expect, stream, set(column.to_scan))
 
             return next_set
 

lark/parsers/xearley.py

@@ -112,7 +112,7 @@ class Parser:
             del delayed_matches[i+1]    # No longer needed, so unburden memory
 
             if not next_set and not delayed_matches:
-                raise UnexpectedInput(stream, i, text_line, text_column, {item.expect for item in to_scan})
+                raise UnexpectedInput(stream, i, text_line, text_column, {item.expect for item in to_scan}, set(to_scan))
 
             return next_set