Merge pull request #1479 from charles-cooper/array_index

Allow array index to be uint256

tests/parser/types/test_lists.py

@@ -1,3 +1,8 @@
+from vyper.exceptions import (
+    ArrayIndexException,
+)
+
+
 def test_list_tester_code(get_contract_with_gas_estimation):
     list_tester_code = """
 z: int128[3]
@@ -199,3 +204,53 @@ def test_multi4() -> uint256[2][2][2][2]:
         [[[1, 0], [0, 4]], [[0, 0], [0, 0]]],
         [[[444, 0], [0, 0]], [[1, 0], [0, 222]]],
     ]
+
+
+def test_uint256_accessor(get_contract_with_gas_estimation, assert_tx_failed):
+    code = """
+@public
+def bounds_check_uint256(ix: uint256) -> uint256:
+    xs: uint256[3] = [1,2,3]
+    return xs[ix]
+    """
+    c = get_contract_with_gas_estimation(code)
+    assert c.bounds_check_uint256(0) == 1
+    assert c.bounds_check_uint256(2) == 3
+    assert_tx_failed(lambda: c.bounds_check_uint256(3))
+
+
+def test_int128_accessor(get_contract_with_gas_estimation, assert_tx_failed):
+    code = """
+@public
+def bounds_check_int128(ix: int128) -> uint256:
+    xs: uint256[3] = [1,2,3]
+    return xs[ix]
+    """
+    c = get_contract_with_gas_estimation(code)
+    assert c.bounds_check_int128(0) == 1
+    assert c.bounds_check_int128(2) == 3
+    assert_tx_failed(lambda: c.bounds_check_int128(3))
+    assert_tx_failed(lambda: c.bounds_check_int128(-1))
+
+
+def test_compile_time_bounds_check(get_contract_with_gas_estimation, assert_compile_failed):
+    code = """
+@public
+def fail() -> uint256:
+    xs: uint256[3] = [1,2,3]
+    return xs[3]
+    """
+    assert_compile_failed(
+            lambda: get_contract_with_gas_estimation(code),
+            ArrayIndexException
+            )
+    code = """
+@public
+def fail() -> uint256:
+    xs: uint256[3] = [1,2,3]
+    return xs[-1]
+    """
+    assert_compile_failed(
+            lambda: get_contract_with_gas_estimation(code),
+            ArrayIndexException
+            )

vyper/exceptions.py

@@ -88,6 +88,10 @@ class SyntaxException(ParserException):
     pass
 
 
+class ArrayIndexException(ParserException):
+    pass
+
+
 class CompilerPanic(Exception):
 
     def __init__(self, message):

vyper/parser/parser_utils.py

@@ -8,6 +8,7 @@
 
 from vyper import ast
 from vyper.exceptions import (
+    ArrayIndexException,
     InvalidLiteralException,
     StructureException,
     TypeMismatchException,
@@ -333,9 +334,24 @@ def add_variable_offset(parent, key, pos):
     elif isinstance(typ, ListType):
 
         subtype = typ.subtype
-        sub = [
-            'uclamplt', base_type_conversion(key, key.typ, BaseType('int128'), pos=pos), typ.count
-        ]
+        k = unwrap_location(key)
+        if not is_base_type(key.typ, ('int128', 'uint256')):
+            raise TypeMismatchException('Invalid type for array index: %r' % key.typ, pos)
+
+        if key.typ.is_literal:  # note: BaseType always has is_literal attr
+            # perform the check at compile time and elide the runtime check.
+            if key.value < 0 or key.value >= typ.count:
+                raise ArrayIndexException(
+                        'Array index determined to be out of bounds. '
+                        'Index is %r but array size is %r' % (key.value, typ.count),
+                        pos)
+            sub = k
+        else:
+            # this works, even for int128. for int128, since two's-complement
+            # is used, if the index is negative, (unsigned) LT will interpret
+            # it as a very large number, larger than any practical value for
+            # an array index, and the clamp will throw an error.
+            sub = ['uclamplt', k, typ.count]
 
         if location == 'storage':
             return LLLnode.from_list(['add', ['sha3_32', parent], sub],