Address review comment: Make '%declare rule' fail in post-processing …

…with a nice message.

lark/lark_validator_visitor.py

@@ -11,6 +11,14 @@ def validate(cls, tree: Tree):
         visitor.visit(tree)
         return tree
 
+    def declare(self, tree: Tree):
+        for child in tree.children:
+            assert child.data == "name"
+            assert len(child.children) == 1
+            assert isinstance(child.children[0], Token)
+            if child.children[0].type != "TOKEN":
+                raise GrammarError("Expecting terminal name")
+
     def ignore(self, tree: Tree):
         # Reject everything except 'literal' and 'name' > 'TOKEN'.
         assert len(tree.children) > 0    # The grammar should pass us some things to ignore.

lark/load_grammar.py

@@ -1272,13 +1272,14 @@ def load_grammar(self, grammar_text: str, grammar_name: str="<?>", mangle: Optio
                     self._ignore(*stmt.children)
             elif stmt.data == 'declare':
                 for symbol in stmt.children:
-                    assert isinstance(symbol, Symbol), symbol
-                    is_term = isinstance(symbol, Terminal)
+                    if isinstance(symbol, NonTerminal):
+                        raise GrammarError("Expecting terminal name")
+                    assert isinstance(symbol, Terminal), symbol
                     if mangle is None:
                         name = symbol.name
                     else:
                         name = mangle(symbol.name)
-                    self._define(name, is_term, None)
+                    self._define(name, True, None)
             elif stmt.data == 'import':
                 pass
             else:

tests/test_grammar.py

@@ -6,6 +6,7 @@
 from lark import Lark, Token, Tree, ParseError, UnexpectedInput
 from lark.load_grammar import GrammarError, GRAMMAR_ERRORS, find_grammar_errors, list_grammar_imports
 from lark.load_grammar import FromPackageLoader
+from lark.lark_validator_visitor import LarkValidatorVisitor
 
 
 class TestGrammar(TestCase):
@@ -295,9 +296,41 @@ def test_line_breaks(self):
                 """)
         p.parse('ab')
 
+    def test_declare_rule_lg(self):
+        g = """
+        %declare a
+        start: b
+        b: "c"
+        """
+        self.assertRaisesRegex(GrammarError, "Expecting terminal name", Lark, g)
 
+    def test_declare_rule_ll(self):
+        g = """
+        %declare a
+        start: b
+        b: "c"
+        """
+        l =  Lark.open_from_package("lark", "grammars/lark.lark")
+        t = l.parse(g)
+        self.assertRaisesRegex(GrammarError, "Expecting terminal name", LarkValidatorVisitor.validate, t)
+
+    def test_declare_token_lg(self):
+        g = """
+        %declare A
+        start: b
+        b: "c"
+        """
+        Lark(g)
 
-
+    def test_declare_token_ll(self):
+        g = """
+        %declare A
+        start: b
+        b: "c"
+        """
+        l =  Lark.open_from_package("lark", "grammars/lark.lark")
+        t = l.parse(g)
+        LarkValidatorVisitor.validate(t)
 
 
 if __name__ == '__main__':