feat: allow range(x, y, bound=N) (#3679)

- allow range where both start and end arguments are variables, so long
  as a bound is supplied

- ban range expressions of the form `range(x, x + N)` since the new form
  is cleaner and supersedes it.

- also do a bit of refactoring of the codegen for range

---------

Co-authored-by: Charles Cooper <[email protected]>

docs/control-structures.rst

@@ -287,9 +287,11 @@ Another use of range can be with ``START`` and ``STOP`` bounds.
 
 Here, ``START`` and ``STOP`` are literal integers, with ``STOP`` being a greater value than ``START``. ``i`` begins as ``START`` and increments by one until it is equal to ``STOP``.
 
+Finally, it is possible to use ``range`` with runtime `start` and `stop` values as long as a constant `bound` value is provided.
+In this case, Vyper checks at runtime that `end - start <= bound`.
+``N`` must be a compile-time constant.
+
 .. code-block:: python
 
-    for i in range(a, a + N):
+    for i in range(start, end, bound=N):
         ...
-
-``a`` is a variable with an integer type and ``N`` is a literal integer greater than zero.  ``i`` begins as ``a`` and increments by one until it is equal to ``a + N``. If ``a + N`` would overflow, execution will revert.

tests/functional/codegen/features/iteration/test_for_in_list.py

@@ -1,3 +1,4 @@
+import re
 from decimal import Decimal
 
 import pytest
@@ -700,13 +701,16 @@ def foo():
     """,
         StateAccessViolation,
     ),
-    """
+    (
+        """
 @external
 def foo():
     a: int128 = 6
     for i in range(a,a-3):
         pass
     """,
+        StateAccessViolation,
+    ),
     # invalid argument length
     (
         """
@@ -789,10 +793,13 @@ def test_for() -> int128:
     ),
 ]
 
+BAD_CODE = [code if isinstance(code, tuple) else (code, StructureException) for code in BAD_CODE]
+for_code_regex = re.compile(r"for .+ in (.*):")
+bad_code_names = [
+    f"{i} {for_code_regex.search(code).group(1)}" for i, (code, _) in enumerate(BAD_CODE)
+]
+
 
-@pytest.mark.parametrize("code", BAD_CODE)
-def test_bad_code(assert_compile_failed, get_contract, code):
-    err = StructureException
-    if not isinstance(code, str):
-        code, err = code
+@pytest.mark.parametrize("code,err", BAD_CODE, ids=bad_code_names)
+def test_bad_code(assert_compile_failed, get_contract, code, err):
     assert_compile_failed(lambda: get_contract(code), err)

tests/functional/codegen/features/iteration/test_for_range.py

@@ -32,6 +32,102 @@ def repeat(n: uint256) -> uint256:
         c.repeat(7)
 
 
+def test_range_bound_constant_end(get_contract, tx_failed):
+    code = """
+@external
+def repeat(n: uint256) -> uint256:
+    x: uint256 = 0
+    for i in range(n, 7, bound=6):
+        x += i + 1
+    return x
+    """
+    c = get_contract(code)
+    for n in range(1, 5):
+        assert c.repeat(n) == sum(i + 1 for i in range(n, 7))
+
+    # check assertion for `start <= end`
+    with tx_failed():
+        c.repeat(8)
+    # check assertion for `start + bound <= end`
+    with tx_failed():
+        c.repeat(0)
+
+
+def test_range_bound_two_args(get_contract, tx_failed):
+    code = """
+@external
+def repeat(n: uint256) -> uint256:
+    x: uint256 = 0
+    for i in range(1, n, bound=6):
+        x += i + 1
+    return x
+    """
+    c = get_contract(code)
+    for n in range(1, 8):
+        assert c.repeat(n) == sum(i + 1 for i in range(1, n))
+
+    # check assertion for `start <= end`
+    with tx_failed():
+        c.repeat(0)
+
+    # check codegen inserts assertion for `start + bound <= end`
+    with tx_failed():
+        c.repeat(8)
+
+
+def test_range_bound_two_runtime_args(get_contract, tx_failed):
+    code = """
+@external
+def repeat(start: uint256, end: uint256) -> uint256:
+    x: uint256 = 0
+    for i in range(start, end, bound=6):
+        x += i
+    return x
+    """
+    c = get_contract(code)
+    for n in range(0, 7):
+        assert c.repeat(0, n) == sum(range(0, n))
+        assert c.repeat(n, n * 2) == sum(range(n, n * 2))
+
+    # check assertion for `start <= end`
+    with tx_failed():
+        c.repeat(1, 0)
+    with tx_failed():
+        c.repeat(7, 0)
+    with tx_failed():
+        c.repeat(8, 7)
+
+    # check codegen inserts assertion for `start + bound <= end`
+    with tx_failed():
+        c.repeat(0, 7)
+    with tx_failed():
+        c.repeat(14, 21)
+
+
+def test_range_overflow(get_contract, tx_failed):
+    code = """
+@external
+def get_last(start: uint256, end: uint256) -> uint256:
+    x: uint256 = 0
+    for i in range(start, end, bound=6):
+        x = i
+    return x
+    """
+    c = get_contract(code)
+    UINT_MAX = 2**256 - 1
+    assert c.get_last(UINT_MAX, UINT_MAX) == 0  # initial value of x
+
+    for n in range(1, 6):
+        assert c.get_last(UINT_MAX - n, UINT_MAX) == UINT_MAX - 1
+
+    # check for `start + bound <= end`, overflow cases
+    for n in range(1, 7):
+        with tx_failed():
+            c.get_last(UINT_MAX - n, 0)
+        with tx_failed():
+            c.get_last(UINT_MAX, UINT_MAX - n)
+
+
 def test_digit_reverser(get_contract_with_gas_estimation):
     digit_reverser = """
 @external
@@ -89,7 +185,7 @@ def test_offset_repeater_2(get_contract_with_gas_estimation, typ):
 @external
 def sum(frm: {typ}, to: {typ}) -> {typ}:
     out: {typ} = 0
-    for i in range(frm, frm + 101):
+    for i in range(frm, frm + 101, bound=101):
         if i == to:
             break
         out = out + i
@@ -146,26 +242,28 @@ def foo(a: {typ}) -> {typ}:
     assert c.foo(100) == 31337
 
 
-# test that we can get to the upper range of an integer
 @pytest.mark.parametrize("typ", ["uint8", "int128", "uint256"])
 def test_for_range_edge(get_contract, typ):
+    """
+    Check that we can get to the upper range of an integer.
+    Note that to avoid overflow in the bounds check for range(),
+    we need to calculate i+1 inside the loop.
+    """
     code = f"""
 @external
 def test():
     found: bool = False
     x: {typ} = max_value({typ})
-    for i in range(x, x + 1):
-        if i == max_value({typ}):
+    for i in range(x - 1, x, bound=1):
+        if i + 1 == max_value({typ}):
             found = True
-
     assert found
 
     found = False
     x = max_value({typ}) - 1
-    for i in range(x, x + 2):
-        if i == max_value({typ}):
+    for i in range(x - 1, x + 1, bound=2):
+        if i + 1 == max_value({typ}):
             found = True
-
     assert found
     """
     c = get_contract(code)
@@ -178,7 +276,7 @@ def test_for_range_oob_check(get_contract, tx_failed, typ):
 @external
 def test():
     x: {typ} = max_value({typ})
-    for i in range(x, x+2):
+    for i in range(x, x + 2, bound=2):
         pass
     """
     c = get_contract(code)

tests/functional/codegen/integration/test_crowdfund.py

@@ -52,7 +52,7 @@ def finalize():
 @external
 def refund():
     ind: int128 = self.refundIndex
-    for i in range(ind, ind + 30):
+    for i in range(ind, ind + 30, bound=30):
         if i >= self.nextFunderIndex:
             self.refundIndex = self.nextFunderIndex
             return
@@ -147,7 +147,7 @@ def finalize():
 @external
 def refund():
     ind: int128 = self.refundIndex
-    for i in range(ind, ind + 30):
+    for i in range(ind, ind + 30, bound=30):
         if i >= self.nextFunderIndex:
             self.refundIndex = self.nextFunderIndex
             return

tests/functional/syntax/exceptions/test_invalid_literal_exception.py

@@ -18,13 +18,6 @@ def foo():
     """,
     """
 @external
-def foo(x: int128):
-    y: int128 = 7
-    for i in range(x, x + y):
-        pass
-    """,
-    """
-@external
 def foo():
     x: String[100] = "these bytes are nо gооd because the o's are from the Russian alphabet"
     """,