clean up index access

tests/parser/types/test_lists.py

@@ -212,6 +212,23 @@ def test_array(x: int128, y: int128, z: int128, w: int128) -> int128:
 
 
 def test_array_negative_accessor(get_contract_with_gas_estimation, assert_compile_failed):
+    array_negative_accessor = """
+FOO: constant(int128) = -1
+
+@external
+def test_array(x: int128, y: int128, z: int128, w: int128) -> int128:
+    a: int128[4] = [0, 0, 0, 0]
+    a[0] = x
+    a[1] = y
+    a[2] = z
+    a[3] = w
+    return a[-4] * 1000 + a[-3] * 100 + a[-2] * 10 + a[FOO]
+    """
+
+    assert_compile_failed(
+        lambda: get_contract_with_gas_estimation(array_negative_accessor), ArrayIndexException
+    )
+
     array_negative_accessor = """
 @external
 def test_array(x: int128, y: int128, z: int128, w: int128) -> int128:

vyper/semantics/types/subscriptable.py

@@ -129,10 +129,11 @@ def validate_index_type(self, node):
         # TODO break this cycle
         from vyper.semantics.analysis.utils import validate_expected_type
 
-        if isinstance(node, vy_ast.Int):
-            if node.value < 0:
+        index_val = prefold(node)
+        if isinstance(index_val, int):
+            if index_val < 0:
                 raise ArrayIndexException("Vyper does not support negative indexing", node)
-            if node.value >= self.length:
+            if index_val >= self.length:
                 raise ArrayIndexException("Index out of range", node)
 
         validate_expected_type(node, IntegerT.any())

vyper/semantics/types/utils.py

@@ -1,12 +1,6 @@
 from vyper import ast as vy_ast
 from vyper.ast.pre_typecheck import prefold
-from vyper.exceptions import (
-    ArrayIndexException,
-    InstantiationException,
-    InvalidType,
-    StructureException,
-    UnknownType,
-)
+from vyper.exceptions import ArrayIndexException, InstantiationException, InvalidType, UnknownType
 from vyper.semantics.analysis.levenshtein_utils import get_levenshtein_error_suggestions
 from vyper.semantics.data_locations import DataLocation
 from vyper.semantics.namespace import get_namespace
@@ -146,22 +140,9 @@ def get_index_value(node: vy_ast.Index) -> int:
     int
         Literal integer value.
     """
-    # this is imported to improve error messages
-    # TODO: revisit this!
-    from vyper.semantics.analysis.utils import get_possible_types_from_node
-
     val = prefold(node.value)
 
     if not isinstance(val, int):
-        if hasattr(node, "value"):
-            # even though the subscript is an invalid type, first check if it's a valid _something_
-            # this gives a more accurate error in case of e.g. a typo in a constant variable name
-            try:
-                get_possible_types_from_node(node.value)
-            except StructureException:
-                # StructureException is a very broad error, better to raise InvalidType in this case
-                pass
-
         raise InvalidType("Subscript must be a literal integer", node)
 
     if val <= 0: