The test contract itself is incomplete. Can we make sure we unit test only the introduced change here?

A correct (i.e. compileable) Vyper contract would look like this

from ethereum.ercs import IERC20
from ethereum.ercs import IERC20Detailed


@external
def foo():
    extcall IERC20(msg.sender).transfer(
        msg.sender,
        convert(staticcall IERC20Detailed(msg.sender).decimals(), uint256),
    )

so we could have the following here:

from ethereum.ercs import IERC20
from ethereum.ercs import IERC20Detailed


@external
def foo():
    extcall IERC20(msg.sender).transfer(
        msg.sender,
        convert(staticall IERC20Detailed(msg.sender).decimals(), uint256),
    )

Another example with nested staticcall could be:

from ethereum.ercs import IERC20
from ethereum.ercs import IERC20Detailed


@view
def bar() -> uint256:
    return staticcall IERC20(msg.sender).balanceOf(
        convert(staticall IERC20Detailed(msg.sender).decimals(), address)
    )

In the last example, if you replace view with pure, it will raise the staticcall first instead of:

vyper.exceptions.StateAccessViolation: Cannot call a view function from a pure function

which is the expected behaviour IMO.

some other (not so common, but still) typos are:

• staticcal (that one we should probably also cover)
• statiiccall
• stacticall
• staticcal

although I can imagine such mistakes being made, I don't like the idea that we would reserve 5 keywords just for error reporting (though I don't think such keywords would be used by users anyway)