Ensure singleton types always compare identical #44565
Merged
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This PR ensures the "singleton" types (
any
,unknown
,string
,number
,boolean
,bigint
,symbol
,void
,undefined
,never
, andobject
) always compare identical when their type kind matches, regardless of type object identity. This in particular ensures that theundefined
used to represent a missing property compares identical to the "regular"undefined
.The PR also ensures that
TypeFlags.Boolean
is consistently set on any union of the boolean literal valuestrue
andfalse
. We weren't setting this flag on type alias declarations fortrue | false
.Fixes #44388.