satisfaction.
Previously we used the rules for constant folding in a non-constant
context, meaning that we'd incorrectly accept foldable non-constant
expressions and that std::is_constant_evaluated() would evaluate to
false.
For a type-constraint in a lambda signature, this makes the lambda
contain an unexpanded pack; for requirements in a requires-expressions
it makes the requires-expression contain an unexpanded pack; otherwise
it's invalid.
properly track that it has constraints.
Previously an instantiation of a constrained generic lambda would behave
as if unconstrained because we incorrectly cached a "has no constraints"
value that we computed before the constraints from 'auto' parameters
were attached.
template-parameter-list in a lambda.
This implements one of the missing parts of P0857R0. Mark it as not done
on the cxx_status page given that it's still incomplete.
Richard Smith