Python builder: Cannot change __class__ of the object type

[longhotsummer]

Fixes #30

[longhotsummer]

This seems to happens when address is FAILURE.

[jcoglan]

Hi @longhotsummer, thank you for taking a look at this. I think this specific check will be brittle, as the value subject to extension may be any user-supplied value, if they're using custom actions. Therefore checking that type(value) != object, which happens to be true for the FAILURE sentinel value, is too broad a check.

Instead we have the builder function ifNode_() specifically for this purpose, and I've made the Extension AST node use this, so it applies across all language backends -- see 5081a30.

See also my commend here #30 (comment) on another attempt at fixing this.

[jcoglan]

This should now be fixed as part of the v0.4 release; see https://blog.jcoglan.com/2022/04/01/announcing-canopy-0-4/