Upgrade was originally blocked by this issue: New Error: error TS2590: Expression produces a union type that is too complex to represent. However it seems like changes in our types must have gotten rid of whatever was causing the problem when spreading props.

We do still get some other instances of TS2590, but they're isolated enough that casts may be an acceptable workaround.

Other possibly-related issues:

• Expression produces a union type that is too complex to represent
• an emitter with 239 events breaks type check, throw ts2590 Expression produces a union type that is too complex to represent
• Performance depends on declaration order · Issue #43437 · microsoft/TypeScript · GitHub