Reject tuple reassignment syntax

Author: Poryaei

src/pinescript_validator/parser.py

@@ -234,8 +234,15 @@ def statement(self) -> AST.Statement | None:
 
                 self.consume(TokenType.RBRACKET, 'Expected "]" in destructuring pattern')
                 if self.check(TokenType.ASSIGN):
-                    self.advance()
-                    return self.destructuring_assignment(names, variables, start)
+                    assign_token = self.advance()
+                    if assign_token.value == "=":
+                        return self.destructuring_assignment(names, variables, start)
+                    self.report_error(
+                        'Tuple destructuring uses "=" only. Reassignment with ":=" is not valid in Pine Script.',
+                        assign_token,
+                    )
+                    self.expression()
+                    return None
                 self.current = checkpoint
             except Exception:
                 self.current = checkpoint

tests/test_validator.py

@@ -153,9 +153,14 @@ def test_strategy_negative_pyramiding_is_rejected(self) -> None:
             )
         )
 
-    def test_destructuring_reassignment_is_supported(self) -> None:
+    def test_destructuring_reassignment_is_rejected(self) -> None:
         diagnostics = self.validator.validate_text("[a, b] := foo()")
-        self.assertFalse(any("Mismatched input" in diagnostic.message for diagnostic in diagnostics))
+        self.assertTrue(
+            any(
+                'Tuple destructuring uses "=" only. Reassignment with ":=" is not valid in Pine Script.' in diagnostic.message
+                for diagnostic in diagnostics
+            )
+        )
 
     def test_typed_array_declaration(self) -> None:
         diagnostics = self.validator.validate_text("var box[] mc_boxes = array.new_box()")