Compiler panic when importing interfaces with max_value() as a default argument value

[hadfieldn]

Version Information

• vyper Version (output of vyper --version): 0.3.6
• OS: osx
• Python Version (output of python --version): 3.9.8

What's your issue about?

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• full output of the error you received
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When a contract has a function that uses max_value(uint256) as a default argument value, it causes a compiler panic when it is imported as an interface:

# ContractB.vy (compiles successfully)

@view
@external
def foo(_max: uint256 = max_value(uint256)) -> uint256:
    return _max

# ContractA.vy (fails to compile)

import ContractB as ContractB

Compiling ContractA results in a compile error:

$ vyper ContractA.vy
Error compiling: ContractA.vy
vyper.exceptions.CompilerPanic: max_value should always be folded

This is an unhandled internal compiler error. Please create an issue on Github to notify the developers.

How can it be fixed?

Fill this in if you know how to fix it.

[hadfieldn]

The same failure occurs when the default value is min_value(uint256), but it succeeds with empty(uint256).

[hadfieldn]

As a workaround, if I declare a constant for the default value, it works, but I have to declare the same constant in the contract doing the import:

# ContractB.vy (compiles successfully)

# `MAX_UINT256` is deprecated, so we use `_MAX_UINT256`
_MAX_UINT256: constant(uint256) = max_value(uint256)


@view
@external
def foo(_max: uint256 = _MAX_UINT256) -> uint256:
    return _max

Fails unless _MAX_UINT256 is declared in ContractA:

# ContractA.vy (fails to compile)

import ContractB as ContractB

$ vyper ContractA.vy
Error compiling: ContractA.vy
vyper.exceptions.UndeclaredDefinition: '_MAX_UINT256' has not been declared.
  contract "ContractB", function "foo", line 9:24
       8 @external
  ---> 9 def foo(_max: uint256 = _MAX_UINT256) -> uint256:
  -------------------------------^
      10     return _max

Succeeds:

# ContractA.vy (compiles successfully)

import ContractB as ContractB

_MAX_UINT256: constant(uint256) = max_value(uint256)

$ vyper ContractA.vy
0x61000d61000f60003961000d6000f3a165767970657283000306000b

[charles-cooper]

whoa, that also seems like a bug. you should not be able to override constants in the imported contract from the importing contract.

[hadfieldn]

Also works if I declare the interface inline:

# ContractA.vy (compiles successfully)

interface ContractB:
    def foo(_max: uint256 = max_value(uint256)) -> uint256: view

[hadfieldn]

Related to the need to redeclare constants locally, but probably a separate issue -- if the imported contract references a struct in its function signatures, I also have to declare that Struct in the importing contract.

(I know this was reported in #2670)