internal and pure functions allow to be payable

[pcaversaccio]

Version Information

• vyper Version (output of vyper --version): 0.3.6+commit.4a2124d
• OS: win
• Python Version (output of python --version): 3.9.2

What's your issue about?

The current Vyper version allows for functions decorated via the internal or pure modifier to be payable. In such situations, the compiler should throw an error.

To reproduce this behaviour, you can compile:

@external
def foo() -> Bytes[32]:
    self.bar()
    return b"\x01"

@internal
@payable
def bar() -> uint256:
    return 1

How can it be fixed?

The compiler should throw a type error in such circumstances.

[charles-cooper]

see #3123 (comment) for an alternative way to address this