Currently `simplifyAppliedOverloads` depends on
the order in which constraints are simplified,
specifically that a lookup constraint for a
function gets simplified before the applicable
function constraint. This happens to work out
just fine today with the order in which we
re-activate constraints, but I'm planning on
changing that order.
This commit changes the logic such that it it's no
longer affected by the order in which constraints
are simplified. We'll now run it when either an
applicable function constraint is added, or a new
bind overload disjunction is added. This also
means we no longer need to run it potentially
multiple times when simplifying the applicable fn.
This is a follow up to changes related to contextual availability
(https://github.com/apple/swift/pull/29921) which increased score
for unavailable declarations only if they were overloaded but
overlooked a case of a single unavailable choice.
Resolve: rdar://problem/60047439
Implement support for switch statements within function builders. Cases can
perform arbitrary pattern matches, e.g.,
tuplify(true) { c in
"testSwitchCombined"
switch e {
case .a:
"a"
case .b(let i, _?), .b(let i, nil):
i + 17
}
}
subject to the normal rules of switch statements. Cases within function
builders cannot, however, include “fallthrough” statements, because those
(like “break” and “continue”) are control flow.
The translation of performed for `switch` statements is similar to that of
`if` statements, using `buildEither(first:)` and `buildEither(second:)` on
the function builder type.
This is the bulk of switch support, tracked by rdar://problem/50426203.
Currently constraint solver is only capable of detecting universally unavailable
overloads but that's insufficient because it's still possible to pick a contextually
unavailable overload choice which could be better than e.g. generic overload, or
one with defaulted arguments, marked as disfavored etc.
Let's introduce `ConstraintSystem::isDeclUnavailable` which supports both universal
and contextual unavailability and allow constraint solver to rank all unavailable
overload choices lower than any other possible choice(s).
Resolves: rdar://problem/59056638
Rather than having separate dense maps for the type mappings of each
node type (expression, type location, variable declaration, pattern) that
a TypedNode can be, have a single such map. Sometimes we end up
setting a particular node's type more than once, so cope with that
by restoring the prior type.
Move more constraint generation logic for an expression target into a
new generateConstraints() on a solution target, so we can further
generalize the main “solve” logic.
Capture the peculiarities of contextual types vs. types used to generate
conversion constraints, as well as the behavior of “optional some” patterns
as used by if let / while let, within SolutionApplicationTarget. This allows
us to use a single target throughout setup / solving / application, rather
than mapping between two similar-but-disjoint targets.
Start cleaning up the main “solve” entry point for solving an expression
and applying the solution, so it handles arbitrary solution targets.
This is another small step that doesn’t do much on its own, but will help
with unifying the various places in the code base where we run the solver.
Add the final conversion type and the flag indicating whether a given
expression is discarded to SolutionApplicationTarget, rather than
separating the arguments to the solver implementation.
SolutionResult better captures what can happen when solving a constraint
system for the given expression occurs than the ad hoc SolutionKind return
& small vector of Solution results. Also, try to make this logic less
convoluted.
