Allow Exclude when the difference contains a union.

[estaub]

AFAICT, there is no broadly-functional implementation of Exclude/Omit that works when there's a union in the remaining difference. I'd suggest that perhaps Exclude might be enhanced to handle this case.

The Omit implementations I'm aware of rely on keyof, which doesn't include any members of one union member that aren't present in all. This is by design; see #12948.

2.8's Exclude won't work on such a type at all, complaining that it's not an interface.

This blocked one route in my particular production (one of many!) of "The Failed Quest for a Typescript React HOC Declaration With Generic Inferencing That Works". See mui/material-ui#11003 (likely to be rolled back soon).

[RyanCavanaugh]

Some example code of what you're trying to do would be great

[estaub]

Sorry, this is why one should never write an issue without the code in front of you. I got Exclude and 'extends?' (conditional typing) befuddled. Closing.