Disallow literal 0 step in slice expression

Author: brianschubert

mypy/checkexpr.py

@@ -5616,6 +5616,13 @@ def visit_slice_expr(self, e: SliceExpr) -> Type:
             if index:
                 t = self.accept(index)
                 self.chk.check_subtype(t, expected, index, message_registry.INVALID_SLICE_INDEX)
+
+        if e.stride:
+            stride_literals = self.try_getting_int_literals(e.stride)
+            if stride_literals is not None and 0 in stride_literals:
+                self.msg.fail("Slice step cannot be 0", index)
+                return AnyType(TypeOfAny.from_error)
+
         return self.named_type("builtins.slice")
 
     def visit_list_comprehension(self, e: ListComprehension) -> Type:

test-data/unit/check-expressions.test

@@ -1235,6 +1235,19 @@ a[None:]
 a[:None]
 [builtins fixtures/slice.pyi]
 
+[case testSliceStepZero]
+from typing import Any
+from typing_extensions import Literal
+n1: Literal[0]
+n2: Literal[0, 1]
+a: Any
+a[::0]      # E: Slice step cannot be 0
+a[::-0]     # E: Slice step cannot be 0
+a[::+0]     # E: Slice step cannot be 0
+a[::n1]     # E: Slice step cannot be 0
+a[::n2]     # E: Slice step cannot be 0
+[builtins fixtures/tuple.pyi]
+
 
 -- Lambdas
 -- -------