Detect that result type of the overload choice is l-value and preserve
that information through the forced unwrap operation so it's possible
to load the value implicitly during solution application.
Resolves: rdar://problem/61337704
When we determine that an optional value needs to be unwrapped to make
an expression type check, use notes to provide several different
Fix-It options (with descriptions) rather than always pushing users
toward '!'. Specifically, the errors + Fix-Its now looks like this:
error: value of optional type 'X?' must be unwrapped to a value of
type 'X'
f(x)
^
note: coalesce using '??' to provide a default when the optional
value contains 'nil'
f(x)
^
?? <#default value#>
note: force-unwrap using '!' to abort execution if the optional
value contains 'nil'
f(x)
^
!
Fixes rdar://problem/42081852.
We were failing to bind the alternatives for an IUO @optional
requirement because we forgot to set the appropriate type variable option.
Fixes: rdar://problem/40868990
We were not handling IUO results of @optional protocol methods
properly, sometimes forcing the @optional requirement rather than the
result of the call.
Fixes rdar://problem/37240984.
