bug: make_setter is incorrect for complex types when RHS references LHS with a function call

[tserg]

Version Information

• vyper Version (output of vyper --version): 9e3b9a2
• OS: linux
• Python Version (output of python --version): 3.10.4

What's your issue about?

#2418 described a bug where, during an assignment, if the right-hand side refers to the left-hand side, part of the data to be copied may get overwritten before being copied.

Although #3410 fixed the issue in most of the cases, it can still happen with function calls as shown in the examples below.

In this example, a call to foo() returns [2, 2] when it should return [2, 1].

a:DynArray[uint256,2]

@external
def foo() -> DynArray[uint256,2]:
    # Initial value
    self.a = [1,2]
    self.a = [self.bar(1), self.bar(0)]
    return self.a #returns [2,2]

@internal
def bar(i:uint256)->uint256:
    return self.a[i]

In this example, boo() temporarily assigns values to self.a before emptying it. The values stored in self.a are however still readable from foo() as a fall to foo() here returns [11, 12, 3, 4].

a: DynArray[uint256, 10]

@external
    def foo()->DynArray[uint256, 10]:
    self.a = [1, 2, self.boo(), 4]
    return self.a # returns [11, 12, 3, 4]

@internal
def boo() -> uint256:
    self.a = [11, 12, 13, 14, 15, 16]
    self.a = []
    # it should now be impossible to read any of [11, 12, 13, 14, 15, 16]
    return 3

h/t @trocher

How can it be fixed?

Fill this in if you know how to fix it.