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I’d put brakes on this a bit. It’s an experimental type, it’s too soon to propagate it around the codebase.

My current idea is that there is going to be 3-way setting about “unsafe array string keys”. The default would be current behaviour (unsafe), to not break users’ baselines with more specific types.

I see. lets park it for now and come back after the array-key topic is more mature.

My current idea is that there is going to be 3-way setting about “unsafe array string keys”. The default would be current behaviour (unsafe), to not break users’ baselines with more specific types.

I also tried #5312 on my side @ondrejmirtes.
I won't spend more time on this and let you do it like you want but here's my thought:

• I have some trouble to see how to have this new type efficient without propagating it to the whole codebase
• decimal-int-string&lowercase-string&uppercase-string seems redundant, a decimal-int-string is ALWAYS lowercase and uppercase ; we should:
  • Simplify the description in IntersectionType
  • Avoid adding both when possible
• Breaking the user baseline with more specific seems ok to me in minor, especially when this certainly already occured without people complaining a lot about it when we introduced lowercase-string or uppercase-string ; but if you really want to avoid this, maybe we could just describe the decimal-int-string as numeric-string&lowercase-string&uppercase-string for people with the toggle off.

Yes, decimal-int-string&lowercase-string&uppercase-string is redundant, this should be reduced in TypeCombinator, you can write a test and modify some code in isSuperTypeOf/isSubTypeOf.