Prevent terminals from being filtered out when used in always_accept

lark-stubs/__init__.pyi

@@ -5,5 +5,7 @@ from .visitors import *
 from .exceptions import *
 from .lexer import *
 from .lark import *
+from logging import Logger as _Logger
 
+logger: _Logger
 __version__: str = ...

lark-stubs/lark.pyi

@@ -2,7 +2,7 @@
 
 from typing import (
     TypeVar, Type, List, Dict, IO, Iterator, Callable, Union, Optional,
-    Literal, Protocol,
+    Literal, Protocol, Iterable,
 )
 from .visitors import Transformer
 from .lexer import Token, Lexer, TerminalDef
@@ -14,6 +14,8 @@ class PostLex(Protocol):
 
     def process(self, stream: Iterator[Token]) -> Iterator[Token]:
         ...
+    
+    always_accept: Iterable[str]
 
 
 class LarkOptions:

lark/lark.py

@@ -269,8 +269,13 @@ class Lark(Serialize):
         # Parse the grammar file and compose the grammars (TODO)
         self.grammar = load_grammar(grammar, self.source, re_module)
 
+        if self.options.postlex is not None:
+            terminals_to_keep = set(self.options.postlex.always_accept)
+        else:
+            terminals_to_keep = set()
+
         # Compile the EBNF grammar into BNF
-        self.terminals, self.rules, self.ignore_tokens = self.grammar.compile(self.options.start)
+        self.terminals, self.rules, self.ignore_tokens = self.grammar.compile(self.options.start, terminals_to_keep)
 
         if self.options.edit_terminals:
             for t in self.terminals:

lark/load_grammar.py

@@ -526,7 +526,7 @@ class Grammar:
         self.rule_defs = rule_defs
         self.ignore = ignore
 
-    def compile(self, start):
+    def compile(self, start, terminals_to_keep):
         # We change the trees in-place (to support huge grammars)
         # So deepcopy allows calling compile more than once.
         term_defs = deepcopy(list(self.term_defs))
@@ -641,7 +641,7 @@ class Grammar:
         used_terms = {t.name for r in compiled_rules
                              for t in r.expansion
                              if isinstance(t, Terminal)}
-        terminals, unused = classify_bool(terminals, lambda t: t.name in used_terms or t.name in self.ignore)
+        terminals, unused = classify_bool(terminals, lambda t: t.name in used_terms or t.name in self.ignore or t.name in terminals_to_keep)
         if unused:
             logger.debug("Unused terminals: %s", [t.name for t in unused])
 

tests/test_parser.py

@@ -1781,6 +1781,29 @@ def _make_parser_test(LEXER, PARSER):
             %import bad_test.NUMBER
             """
             self.assertRaises(IOError, _Lark, grammar)
+        
+        @unittest.skipIf(LEXER=='dynamic', "%declare/postlex doesn't work with dynamic")
+        def test_postlex_declare(self): # Note: this test does a lot. maybe split it up?
+            class TestPostLexer:
+                def process(self, stream):
+                    for t in stream:
+                        if t.type == 'A':
+                            t.type = 'B'
+                            yield t
+                        else:
+                            yield t
+
+                always_accept = ('A',)
+
+            parser = _Lark("""
+            start: B
+            A: "A"
+            %declare B
+            """, postlex=TestPostLexer())
+
+            test_file = "A"
+            tree = parser.parse(test_file)
+            self.assertEqual(tree.children, [Token('B', 'A')])
 
         @unittest.skipIf(PARSER != 'earley', "Currently only Earley supports priority in rules")
         def test_earley_prioritization(self):