initializing a RequirementMachine for a written protocol signature.
These generic parameters are used for re-sugaring when computing a
type from a term, so if the recorded 'Self' parameter is canonicalized,
it shows up in diagnostics as 'tau_0_0'.
See the comment at the top of ConcreteContraction.cpp for a detailed explanation.
This can be turned off with the -disable-requirement-machine-concrete-contraction
pass, mostly meant for testing. A few tests now run with this pass both enabled
and disabled, to exercise code paths which are otherwise trivially avoided by
concrete contraction.
Fixes rdar://problem/88135912.
The conflicting rule here is the permanent 'identity conformance'
([P].[P] => [P]). Permanent rules cannot be marked as conflicting,
so just check for this condition first.
